Theory of ideas

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Overview of the theory of ideas

Doctrine of ideas is the modern term for the philosophical conception going back to Plato (428 / 427–348 / 347 BC), according to which ideas exist as independent entities and are ontologically superior to the area of ​​sensually perceptible objects . Such ideas are called “platonic ideas” to distinguish them from modern linguistic usage, in which “ideas” are ideas, thoughts or models. The theories of other philosophers are also referred to by the term "doctrine of ideas", but reference to Plato and Platonism is by far the most common use of the term.

Platonic ideas are for example "the beautiful in itself", "the just in itself", "the circle in itself" or "the human being in itself". According to the doctrine of ideas, ideas are not mere representations in the human mind, but an objective metaphysical reality. The ideas, not the objects of sensory experience, represent actual reality. They are perfect and immutable. As archetypes - decisive patterns - of the individual perishable sense objects, they are the prerequisite for their existence. Plato's conception of ideas is thus in polar contrast to the view that the individual things make up the whole of reality and that behind the general terms there is nothing but the need to construct categories of order to classify the phenomena.

Since the doctrine of ideas in Plato's works is not systematically carried out and is nowhere expressly referred to as teaching, it is disputed in research whether it is a uniform theory at all. An overall picture can only be deduced from the numerous scattered information in Plato's dialogues . In addition, communications from other authors are used, but their reliability is controversial. In addition, the conception of ideas does not play a role in some dialogues, is only hinted at or is even criticized, which has led to the assumption that Plato only represented it temporarily. He did not explicitly address the ideas until the middle phase of his work, but the conception already seems to be in the background in early dialogues. In the intense research debates, the position of the “Unitarians”, who believe that Plato consistently represented a coherent point of view, runs counter to the “development hypothesis” of the “revisionists”. The "revisionists" differentiate between different phases of development and assume that Plato gave up the conception of ideas in his last creative period or at least saw a serious need for revision.


In his statements on the conception of ideas, Plato did not introduce any fixed terminology, but resorted to various expressions in everyday language. For the later so-called "platonic ideas" he mainly used the words idéa and eídos , but also morphḗ (shape), parádeigma (pattern), génos (gender, here: genus), lógos (here: essence), eikōn (image ), phýsis (nature) and ousía ( being , essence, "beingness"). He often paraphrased the “platonic idea” of something with expressions such as “(the thing in question) itself”, “in itself” or “according to its nature”.

The most important terms that are decisive for the reception of the theory of ideas are idea and eidos . Both referred to in common parlance a visual impression and were usually used synonymously. What was meant was the appearance of something that is seen and makes a certain impression: the appearance, the shape or shape, the external appearance, which is described as beautiful or ugly, for example. Idea is derived as a verbal abstract from idein “behold”, “recognize” ( aorist to horan “see”).

In contrast to the original meaning of the word idea , which refers to the visible appearance of something, the Platonic idea is something invisible that underlies the visible appearances. But it can be grasped spiritually and thus “visible” to Plato in a figurative sense. That is why he transferred the term idea from the field of sensory perception to that of a purely spiritual perception. The spiritual "seeing", the "seeing" of the ideas plays a central role in Platonism.

A starting point for this shift in meaning from the visual impression made by a concrete individual thing to something general that can only be grasped mentally was already the use of the term in common parlance, which included the general and abstract: not only individual individuals, but also groups and groups had a certain eidos according to which they were distinguished. So there was a royal and a slave eidos and an eidos of ethnic groups. Another important factor was the fact that the words eidos and idea not only denoted a species-specific appearance, but also, in a derived sense, its “typical” carrier characterized by the appearance. What was meant then was the totality of the elements of a set: a type or a type, a class of people, things or phenomena that is constituted by certain - not just optical - characteristics. In this sense, doctors called one type of patient eidos . Another abstraction step already taken in common linguistic usage was the use of eidos for non-visual circumstances, for example different approaches, ways of life, forms of government or types of malice or war. The classification of character traits, attitudes and behaviors on the basis of the respective eidos - a species-specific quality that constitutes the species - became groundbreaking for Plato's philosophical use of the term: He asked, for example, about the “idea” of a virtue as what constitutes this virtue. So eidos and idea became the philosophical terms for what makes something what it is.

Plato's pupil Aristotle , who rejected the theory of ideas, took up the terminology of his teacher, but modified it for his purposes. He mostly used the term idea to designate the “platonic ideas” whose existence he denied, and with eidos he usually referred to the “form” of a sensually perceptible individual thing that, as the cause of the form, gives shape to matter. However, he did not consistently make this terminological distinction.

Cicero , an important mediator of Platonic ideas in the Latin-speaking world, contributed to the fact that idea also became a philosophical technical term in Latin. He wrote the word in Greek as a foreign word, but later authors usually use the Latin script. Other Latin translations of the philosophical terms eidos and idea were forma ("form"), figura ("shape"), exemplar ("pattern"), exemplum ("pattern", "model") and species ("shape", "pattern." "," Type "). Seneca spoke of "Platonic ideas" (ideae Platonicae) . The late antique translator and commentator of Plato's dialogue Timaios , Calcidius , also used expressions such as archetypus , archetypum exemplar or species archetypa (“archetypal pattern”).

The church father Augustine saw Plato as the originator of the term “ideas”, but said that the content of the term must have been known long before his time. This is to be rendered in Latin with forma or species ; The translation ratio is also acceptable, if not exactly, since ratio actually corresponds to the Greek word logos .

Medieval philosophers and theologians adopted the ancient Latin terminology of the doctrine of ideas, which Augustine, Calcidius and Boethius in particular conveyed to them. In addition to the Latinized Greek word idea, they also used the purely Latin expressions already in use in antiquity to denote the Platonic ideas, especially forma .

In modern German-language research literature, when Plato's conception is mentioned, the expression "ideas" is predominantly used, while in English-language research literature mainly "forms" but also "ideas" are used. Some German-speaking authors speak of "forms" who are strongly oriented towards the Anglo-Saxon tradition. However, this translation has the disadvantage of being based on a linguistic regime that is based on the Aristotelian way of thinking.

Starting points for the development of the theory of ideas

Eleatic and Heraclitic thinking

A starting point for the emergence of the doctrine of ideas offered Plato's examination of two opposing directions of pre-Socratic philosophy: the way of thinking of the Eleates and those of Heraclitus and the Heraclitees. In Heraclitus' worldview, being and becoming are intertwined and condition one another as two aspects of a unified, comprehensive world order. Reality is not static, but process-like, but subject to an eternal regularity and to that extent also constant. The Eleatic school, which referred to the philosopher Parmenides , who was valued by Plato , interpreted being and becoming in a radically different way . The Eleatons denied the reality of the world of growth and decay and declared all sensory perceptions to be illusory. They contrasted this area of ​​a pseudo-reality with a world of unchangeable being as the only reality. Since sensory perception is deceptive, it can neither establish knowledge nor refute results obtained in a purely spiritual way. Knowledge can only refer to unchangeable being. Plato took up core elements of this doctrine: both the concept of a single unchangeable realm of being, closed to the senses but accessible to the human mind, as well as the fundamental distrust of sensory perception. Like Parmenides, he only considered the unchangeable - ideas in his terminology - to be essential and greatly devalued everything material and transitory.

In contrast to Parmenides, who denied any existence to the changeable as non-existent, Plato granted the realm of changeable sense objects a conditional and imperfect being. His concept of a hierarchically graded being connected the realm of ideas as the cause with the sense objects as the cause. In doing so, like Heraclitus, albeit in a different way, he established a connection between being and becoming. Parmenides had declared such a connection to be ruled out.

The philosophical definition

A further impetus was the philosophical questioning of definitions, which already played a central role for Plato's teacher Socrates (the “what is? Questions”). Perhaps already with Socrates, at the latest in Plato's early creative phase, the view developed that a definition not only serves as a terminological convention for the purpose of linguistic understanding, but is objectively right or wrong, depending on whether it is the essence (nature) of what is being designated correctly reproduces. The definition should therefore serve directly to gain knowledge. Anyone who found the right definition had grasped the essence of the thing referred to - for example a certain virtue - and was then able to apply this knowledge in their everyday life. The subjects the philosophers were concerned with were exclusively abstract entities such as beauty, “goodness”, justice or bravery. It was assumed that there can only be philosophical knowledge of the general, not of the individual. The idea that the epistemological primacy of the general corresponds to an ontological one was obvious. This could lead to the assumption that the actual reality consists in the essence of the general objects considered and that these are ontologically independent entities. Such considerations probably paved the way for Plato's view that general objects have a prominent existence in a particular area.

The philosophy of mathematics

It was probably through his preoccupation with geometry that Plato came up with the idea that there is a connection and a sharp, fundamental opposition between the graphic and the abstract. It struck him that geometrical thinking is based on the fact that certain shapes, such as the circular shape, are sensually perceived and examined, and thereby general knowledge that applies to the "circle itself" is gained. The "circle in itself" as an object of mathematical statements is not perceptible to the senses anywhere, but its properties are decisive for the nature of every visible circle. Although the circles of the sensory world differ in their different sizes and different degrees of approximation to the ideal circular shape, they are all the same in terms of what constitutes their circular character. As drawn objects, they are necessarily imprecise images of the imaginary ideal circle, that is, the Platonic idea of ​​the circle. For Plato, this idea turned out to be the pattern and archetype on which all visible circles are based. He saw here a relationship between archetypal image and images, whereby all images owe their existence to the archetype.

The fundamental difference between physical and geometric objects was already known in Plato's time; what was new was the ontological interpretation he gave it. He pointed out that mathematicians assume their concepts (such as geometrical figures or types of angles) are known and use them as a basis for their proofs as if they knew about them. But they are unable to clarify their concepts and to give an account of themselves and others about what the things they refer to are in reality. They relied without justification on alleged evidence, on unquestioned assumptions. Although the mathematical subject area is intellectual and therefore fundamentally accessible to knowledge, the mathematicians had no real knowledge about it. Such knowledge cannot be reached in a mathematical way, but only in a philosophical way: through insight into the character of ideas of mathematical objects.

Plato saw the point of studying mathematics in the fact that it clarifies the contrast between sensual and nonsensual contemplation, between perfect archetypes and always defective images, and at the same time directs one's gaze from the visible images to the only mentally comprehensible archetypes. Therefore, from a didactic point of view, he viewed mathematics as an important preparation for philosophy. What applies to the circle should also apply analogously to ethical and aesthetic issues. It was only in this propaedeutic function for the doctrine of ideas, not in the results of individual mathematical investigations, that Plato saw the value of mathematics for the philosopher.

Outlines of Plato's conception

Plato, Roman copy of the Greek portrait of Plato by Silanion , Glyptothek Munich

Despite the ambiguity of many details, Plato's scattered statements about the ideas result in an overall framework within which text-oriented interpretations have to move.

Characteristics of the ideas

The main characteristics of the ideas resulting from Plato's statements are:

  • They are intelligible , that is, incorporeal, in principle withdrawn from the senses and can only be grasped through spiritual insight.
  • They are “pure beings” and “beings beings”, that is, being in the real, proper sense belongs to them only. All being outside the realm of ideas is only a derived being, a being in an improper sense.
  • They are perfect, that is: the specific essence of the person whose incorporeal “shape” is an idea finds its perfection in it which cannot be surpassed. This gives the ideas a value dimension, they are positively assessed and glorified as ideals by Plato. In the idea, what is coincides with what should be.
  • They are timeless, that is, they do not arise and do not perish and are not subject to any change, but always identical with themselves. Their eternity is to be understood in the sense of timelessness; From a temporal perspective, it appears to be of unlimited duration.
  • They are formless, that is, they cause the spatial shapes, but they have no shape themselves because they are not spatial. Since they have no space, they are nowhere.
  • They are simple, pure and unmixed. You are the one in which what is corresponds exactly with what it shows itself to be. An idea is what it means. It only represents itself, in contrast to the sense object, which points beyond itself to the world of ideas. While a sense object, as a bearer of contrary characteristics, contains an inner opposition - for example, it is beautiful in one respect and ugly in another - an idea cannot have anything but its own nature.
  • They are normative, that is, they cause everything that can be sensed to exist and to be as it is. The real being of ideas is the cause of the improper being of changeable things. The ideas are archetypes, all changeable things are their images. The sense objects owe everything they are and what can be perceived about them to the ideas. The ideas, on the other hand, owe nothing to the individual things; their existence is in no way dependent on that of the individual things.
  • There are ideas only from the general, not from individuals.
  • The idea as the universal with its comprehensive character is the principle of unity for the sense objects in the multiplicity of which it is represented.
  • Because of their characteristics, which are of a divine nature, the ideas are divine beings and as such are superior to the gods; the gods owe their divinity to their access to ideas.
  • As an object of knowledge, an idea is a source of knowledge. Knowledge related to ideas that is not based on sensory perception means real knowledge, while sensory perception only leads to opinions due to a lack of reliability.

The area of ​​ideas and its order

The hierarchy of intelligible entities

Plato's definition of the term "angler"

As incorporeal and non-spatial entities, the ideas cannot be localized, they form an area that can only be grasped spiritually (noētós tópos) . In this entire area there is perfect order with a hierarchical structure. Within the framework of this order, relationships exist among ideas. They are partly intertwined; Plato compares these connections with those of letters and tones. Some mix with one another, others don't accept one another. The scope of meaning is decisive for the hierarchical gradation: The more general is always the greater and higher-ranking, since it includes the more specific. The lower has a share in the higher (participation ratio). At the top is the most comprehensive idea, the idea of ​​the good. Subordinate to it are the five “greatest genres” that Plato names in his dialogue Sophistes : the being (on) , the movement (kínēsis) , the immutability (stásis) , the identical (tautón) and the different (tháteron) . The idea of ​​the beautiful is one of the great and important ideas.

The ranking of the ideas is determined using the method of dihairesis (subdivision), which shows the superordinate and subordinate relationships of terms and thus at the same time opens up the structure of the area of ​​ideas. The more general is broken down step by step into more specific ones by breaking down a superordinate term into sub-terms using suitable features, which are then also broken down. The “species-forming difference” is added to a generic term and the species terms subordinate to the generic term are thus obtained. Then one proceeds in the same way from one of the identified species to its subspecies. Starting from a top genus, by continuously differentiating, one forms a series until one arrives at a term that cannot be further subdivided, with which one has reached an "indivisible species" (átomon eidos) . This results in a fixed number of intermediate links between the top genus and the indivisible species. This allows both the definition of the indivisible species and the structure of the hierarchical order to be recognized in the relevant sub-area of ​​the realm of ideas.

In addition to the participation of the lower ideas in the higher ones, Plato also assumes a mutual participation. The term community (koinōnía) is used to denote the interweaving of ideas .

The role of the idea of ​​good

A main characteristic of the hierarchical order in the area of ​​ideas is the special role of the idea of ​​the good. This idea sharply distinguishes Plato from the other ideas. He gives it a unique primacy. According to his teaching, all other ideas owe their existence to this one idea. Thus they are ontologically subordinate to it. The idea of ​​good is the supreme principle and cause of the being and goodness of everything. Only by participating in it are the other ideas good and therefore valuable. It is also the principle of order; as such it permeates the whole realm of pure being and gives it its structure.

The ontological status of the idea of ​​the good is very controversial in research. The starting point of the debates is a passage in Plato's interpretation of his allegory of the sun , where it is stated that the good is “not the Ousia ” but “beyond the Ousia” and surpasses it in originality and power. The term Ousia (literally “beingness”) is usually translated as “being” or “being”; both meanings occur in Plato. It is discussed what meaning is present here and how literally the statement is meant.

If Ousia means being and the passage is interpreted literally, “beyond the Ousia” is to be understood in the sense of an absolute transcendence . Then it is asserted here that the idea of ​​the good is superordinate to the unchangeable and perfect being of the purely spiritual reality, thus in relation to this perfect being transcendent (“being transcendent”). According to this, the idea of ​​the good differs in principle from all other ideas in that it gives being to others, but does not itself belong to the realm of being, but exceeds it. As the cause of this entire area, it is ontologically to be located above it; it is “overseeing”.

If, on the other hand, only the essence is meant by “Ousia” or if the passage is interpreted more freely, the idea of ​​the good can be located within the realm of the timeless being of ideas. Accordingly, it is not a question of "being overseas", but only of a particular being that differs from the being of other ideas. One hypothesis is that the idea of ​​the good only transcends the being which it gives to other ideas, not its own being. In favor of this interpretation, a number of statements by Plato can be cited, which show that he - at least from a certain point of view - considered it legitimate to classify the good in the realm of being. For example, he called it “the most blessed of all beings” and “the most brilliant of all beings”.

Ideas and principles

One of the most difficult subject areas in Plato research is the "doctrine of principles". It is considered by some researchers to be a central part of Platonic philosophy. The tradition is unfavorable, because the content of this doctrine can be found in Plato's dialogues at most allusions. The doctrine of principles can only be inferred from an indirect tradition. In research, however, opinions differ widely about the credibility and interpretation of the information in the sources. The spectrum ranges from the hypothesis that the sources do not deserve trust and that Plato did not have a doctrine of principles to the assumption of a completed metaphysics and extensive attempts at reconstruction.

In the opinion of proponents of the authenticity of the doctrine of principles, Plato did not expose it in writing because he considered it to be so demanding that it was not suitable for writing down and above all for publication. He was of the opinion that the doctrine of principles could only be made comprehensible to a competent audience and that the only meaningful framework for it was oral lessons. According to this line of research, the source evidence is based on reports of Plato's oral teaching in the Academy . Because of the restriction to oral transmission, the doctrine of principles is also called Plato's "unwritten doctrine" - with recourse to a formulation by Aristotle.

In terms of content, Plato is said to have been concerned with bringing the project of reducing multiplicity to unity, which the theory of ideas served, to a consistent conclusion. He traced the diverse world of sensory objects back to the ideas that he viewed as the origins of everything that could be sensed. In doing so he reduced the diversity of the material world of appearances to the simple, general principles underlying the individual things. However, Plato's area of ​​ideas also has an unmistakable multitude of elements, since every concept corresponds to an idea. Thus the introduction of the ideas was only one stage on the way from the maximum multiplicity in the world of appearances to the greatest possible unity. This resulted in the endeavor for Plato to reduce the number of origins and to reduce the ideas to a few basic principles. In the dialogues there are various approaches that point in this direction: the hierarchical structure of the intelligible realm, the primacy of the idea of ​​the good, which protrudes above the other ideas, and the division of all beings into four genres presented in Philebo 's late dialogue : that Unlimited, the limitation, the mixture of these two and the cause of the mixture. With the search for the simplest possible origin of all the diversity and complexity of intelligible and material things, Plato embraced a concern of the pre-Socratics , who had given different answers to the question of universal original principles .

After the reconstruction of the doctrine of principles based on the sources, Plato wanted to explain the existence of ideas with this doctrine, just as he explained the existence of the phenomenal world with the doctrine of ideas. He adopted two fundamental principles: the one (to hen) as the principle of unity and the “unlimited” or “indefinite” duality (ahóristos dyás) . He also called the unlimited duality the “big and small” (méga kai mikrón) . He saw in it the principle of diminishing and multiplying, of ambiguity and indeterminacy, and of multiplicity. In the doctrine of principles, the world of ideas was traced back to the connection of the two original principles, the ultimate foundations. The relationship between the two original principles is unclear. What is certain is that Plato - if he actually represented the doctrine of principles - ontologically assigned a higher rank to the one than to the unlimited duality.

What needs to be clarified for the proponents of the authenticity of the doctrine of principles is the fact that in this model the one is at the top of the hierarchy, while Plato in the dialogue Politeia makes the idea of ​​the good the highest principle. The assessment of the relationship between the one and the good is related to the controversial question of the transcendence of being of the good. The researchers who advocate the authenticity of the doctrine of principles are usually also advocates of the transcendence of the good. For most of them this results in equating the idea of ​​the good with the one. “The good” and “the one” are then just two synonymous terms for the one highest primal principle of all reality. This is how the ancient Neo-Platonists understood Plato's teaching.

Ideas and sensory objects

On the one hand, the realm of ideas and the visible cosmos are completely different in nature; on the other hand, there is an ontological causal relationship between them. Plato tries to illustrate with paraphrases and by means of a mythical representation how he imagines the separation of the two areas and at the same time the effect of one on the other. The sensually perceptible “things”, the causes of which are ideas, are not only to be understood as material objects, but also events and actions.

The contrast between ideas and sense objects

The relationship between ideas and sense objects is characterized by its one-sidedness and by the opposing nature of the two classes of entities. This shows up in a number of ways:

  • The ideas give the sense objects being and essence, thus shape the entire existence of the sense world; the sense objects, however, have no influence on the intelligible realm. The ideas, as archetypes, are the generating entities, the sense objects, as images, are the products. Every sense object owes its existence and its species-specific nature to the objective being and the peculiarity of the idea on which it is based. For example, there are horses with their typical characteristics because there is the idea of ​​the horse. For the idea of ​​the horse, however, it does not matter whether there are horses on earth or not.
  • The ideas represent the actual reality, the objects of the sensory experience only a derived reality.
  • The ideas show an unchangeable being, the sensually perceptible objects due to their changeability and transience only a time-dependent and thus deficient being.
  • The ideas are perfect, the mode of existence of the sensually perceptible objects, on the other hand, is characterized by imperfection. For example, a single thing always has only a limited, relative beauty. It can be surpassed by something more beautiful, or it can lose its beauty, and it is only partially or in a certain way beautiful. The idea of ​​the beautiful, on the other hand, is withdrawn from such more or less, because the beautiful as an idea is absolutely beautiful (without gradation or restriction).
  • Every idea excludes its opposite. Sensory objects, on the other hand, are always something and at the same time its opposite. Every beautiful sensory object also has an ugly aspect. A single hot thing is not entirely free from cold, and a cold thing is not free from heat. With "hot" only a predominance of the heat is expressed.

The connection between ideas and sense objects

In view of the radical essential difference between the realm of ideas and the world of material phenomena, the question arose for Plato as to how there could be a connection between the two realms. It was necessary to explain how the separately existing ideas can have an effect on physical matter and how the connection between spiritual and material that is characteristic of the visible cosmos can come about. A mediating authority or a mediating principle was required for the explanation.

Mythical representation

On the mythical level, Plato illustrates mediation by introducing a creator god as the mediating authority. In the dialogue Timaeus he tells a creation myth that offers a detailed explanation of the world order. The demiurge (god of creation) creates the cosmos according to the pattern (parádeigma) of the ideas he looks at. Among them are the ideas of the elements and of all living beings and the idea of ​​eternity as a model of time. The visible cosmos in its entirety, like each of its components, is an image of what the Demiurge saw in the realm of ideas.


In the context of his philosophical interpretation of the connection between ideas and sensory objects, Plato uses the term “participation” ( Methexis ). This means that a sense object “participates” in an idea because, with certain restrictions, it exhibits the nature of the idea and is thus to a certain extent “involved” in its nature. The idea gives sense objects certain aspects of their own being, as far as the limited capacity of the material to absorb and realize this allows. Because the participating sense objects do not have the essence of the idea in its entirety, but only in a relatively incomplete, imperfect way, and because they also have other determinations, participation does not mean essential equality.

When a sense object participates in an idea, it is “present” in it. This presence or presence (parousía) of ideas in the visible cosmos cannot be understood spatially.

Every thing has a share in several or many ideas and every idea allows a multitude of things to have a share in its essence. This is how the multiplicity of things comes about. Participation in ideas enables things to owe all of their properties except for their materiality. For example, a great thing is great only because of its participation in the idea of ​​greatness, not because of a nature it inherently has. Each individual thing receives its special quality through the interaction of the various ideas that are involved in its design and give it the entirety of its characteristics (size, color, etc.). Thus the individual thing is constituted by its various participatory relationships. It participates in as many ideas as it has properties.

The respective type of participation determines to what extent something has the special quality that it receives from a particular idea. How righteous a person is is determined by the degree of his participation in the idea of ​​the righteous.

In some cases a thing's participation in an idea is not constant; it can grow and decrease, begin and end through changes in the participant. There is a kind of participation that is inseparable from the essence of a thing (for example the participation of the immortal soul in life), and an only temporary participation that arises or disappears (for example the participation of a body in rest or movement).

The participation of a thing in ideas is based exclusively on the fact that it absorbs their properties in a purely passive manner. In humans, on the other hand, an active role of the participant comes into play: He participates in the ideas of individual virtues and abilities because he strives to achieve these qualities.

Not completely everything that can be said about a sense object can be explained through the participation of an image in ideas; the materiality of the individual things and their presence in a certain place must have another reason. Plato discusses this additional factor, the “third genus” (next to archetype and copy) in the dialogue Timaeus . The third genre is the principle of materiality and spatial positioning. It is a receptive substrate that Plato compares to a wet nurse and a mother.


In later dialogues, Plato no longer used the term participation for the relationship between things and ideas, but characterized it with terms that refer to the relationship between the archetype and the image. The aspect of imitation ( mímēsis ) comes to the fore . It indicates the normative character of the ideas. The becoming of the ephemeral is the imitation of the being of the unchangeable being. The idea as a prototype is the unattainable model of its images and thus the yardstick for their quality. The souls of people who are exposed to the imperfections and instability of the sensory world can find the natural norms that are authoritative for them in the realm of ideas.

The better a living being or other thing of a certain species copies the idea of ​​this species, the more faithfully it reproduces its species-specific model, the closer it approaches its best form. It realizes its specific aretḗ (suitability, excellence) through good imitation . In doing so, it does its job properly and plays the role that it naturally has. In humans, the arete is the virtue that he acquires by orienting himself on the ideas of virtues.

Monism: the total reality as a unit

Through the “presence” of ideas in the transitory things in which they are “indwelling”, through participation or imitation, there is a community (koinōnía) between ideas and sense objects . It is expressed linguistically in the fact that the individual things have the same names as the species to which they belong.

For Plato, the simple, general and comprehensive is always the ontologically primary. He also emphatically assigns a necessary unitary character to the multiplicity principle. Without it, it could not be a principle and represent the unified superordinate genre for its diverse manifestations. As a unity, the multiplicity principle can neither be of the same origin nor independent of the One, so only a subordination relationship comes into consideration. Because of the primacy of unity, Plato's view of the world is ultimately monistic, despite the sharp, difficult-to-bridge contrast between ideas and sense objects, being and becoming . The existence of two original principles in the doctrine of principles can also be interpreted monistically in the sense of an ontological hierarchy between them. The weighting of the monistic and the dualistic aspects of Plato's thinking and their relationship to one another is, however, controversial in research.

In the research literature, Plato's concept is often referred to as the “two-worlds theory” or “two-worlds model” because of the assumption of a separate realm of ideas that is not accessible to any influence. The appropriateness of such terms is disputed. It depends on whether “worlds” mean two different components of a single reality or two separate realities, between which there can be no explainable mediation despite “participation” and “imitation”. In his works, Plato only circumscribed, not explained, mediation. From this, however, it cannot be concluded that he considered the mediation problem unsolvable or that he denied the existence of mediation.

Rafael Ferber , Michael Erler and Giovanni Reale , among others, emphasize the ontological diversity of the intelligible realm and the realm of sensory perception and thus the justification of terms such as “two-world theory” . Historians of philosophy follow a completely different approach, who attribute the assumption that Plato had a “two-world concept” to a misunderstanding. Paul Natorp and Theodor Ebert emerged as spokesmen for this research area . According to Ebert's interpretation, the distinction between image and original is not to be understood in the sense of an ontological difference, but in a functional sense with reference to a cognitive process. According to this interpretation, Plato does not distinguish between levels of reality and corresponding levels of knowledge, but between a means of knowledge and what is known with the help of this means; he does not proceed from a division of the world into two parts, but from the indivisibility of the faculty of knowledge. John N. Findlay and Christoph Quarch also oppose a dualistic interpretation of Plato's ontology . Richard Lewis Nettleship had already expressed himself in this way in the 19th century .

Ideas and knowledge

Ideas cannot be grasped through sensual perception, but solely through spiritual insight (nóēsis) . The authority responsible for this in humans is the nous (intellect), whose activity Plato describes as looking. Looking is to be understood metaphorically, since the viewed objects are beyond the spatiotemporal level. The human intellect has access to ideas because of its essential affinity with ideas, for similar things are recognized through similar things.

Knowledge of ideas as a goal in life

For Plato, all striving for knowledge aims at the real. By this he means that which is true in every respect - always, everywhere and necessarily. From a philosophical point of view, knowledge can only be satisfactory for him from such circumstances. This knowledge requires a justification, which must also relate to the realm of the unchangeable.

Since the world of sense objects is constantly changing, it is impossible to say absolutely true about them in any way. Hence there can only be a philosophically satisfactory knowledge of the ideas, because only the ideas are simple and always identical with themselves. The sensory world cannot be considered as an object of philosophical knowledge because of its changeability and contradiction, its lack of clarity and unambiguity and because of the unreliability of sensory perception. But those who have gained knowledge of the ontologically predominant area of ​​ideas also acquire the ability to understand and master existence in the material world of appearances. From the understanding of the archetypes, their images can be understood. When the philosopher has gained insight into the absolutely true and eternally valid that he finds in the realm of ideas, he can orientate himself in the dependent world of becoming and passing away, name things correctly and generally behave correctly. Equipped with the knowledge of ideas, he can explain nature as well as guide a state wisely.

The ideas that are central to the way of life are the ideas of virtues. Plato calls them the "greatest objects of knowledge" (mégista mathḗmata) . The highest goal of knowledge is the idea of ​​the good; it ranks highest among ideas.

The anamnesis theory

With the anamnesis concept, Plato wants to make it understandable how one can advance to the knowledge of ideas from the world of the senses. He is based on his conviction that the soul is not only immortal, but also pre-existent, that is, that it exists both before the formation of the body and after its death. According to the doctrine of the migration of souls , it is not naturally connected to a specific body, but inhabits and animates many bodies one after the other, so it goes through numerous earthly lives. In the time between two earthly lives she is bodiless and stays in an otherworldly area. There she has the opportunity to look at the ideas in a “heavenly place”. Since this perception is directed towards the ideas themselves and not towards the objects of the sense organs that are merely similar to them, it is not afflicted with the uncertainty and the defects of the deceptive sensory perceptions. Rather, it is a matter of an immediate and error-free perception of the area of ​​ideas. The expression "heavenly place" is to be understood as a metaphor for a transcendent area, since the ideas are not spatial.

The knowledge of the ideas obtained on this way is the soul's “very own knowledge”, which is always preserved in it, but is usually hidden during earthly life. Through the connection with an earthly body, the cognitive abilities of the soul are severely impaired and it no longer has direct access to its knowledge of ideas. Although it basically retains the ability to remember it, it needs an impetus to activate this ability and trigger a search for the lost knowledge. For example, looking at individual sense objects in the soul can evoke memories of the ideas that these things are images of. The impetus for the anamnesis can come from sensory impressions that require a conceptual interpretation, or from a discussion that encourages research. Since nature forms a unified whole that is familiar to the soul in its entirety, every observation and every hint can give such an impetus and trigger a memory of a certain forgotten detail. From this memory, access to other details can be gained. The only requirement for this is the necessary perseverance.

Discourse and show

In the context of a philosophical conversation, the anamnesis does not take place as a single step from ignorance to knowledge, but as a discursive cognitive process based on arguments. In doing so, a mere correct opinion turns into understanding, which can be accounted for. Despite the discursive character of the process, Plato also likes to use the metaphor of looking in this context. What the observer “has before his eyes” is the known, to which he has found access in the process of knowledge. The looking subject is the soul. Therefore, Plato uses the metaphor “eye of the soul”. The eye of the soul is drawn out of the “barbaric morass” in which it was buried and directed upwards through dialectics , the philosophical method of gaining knowledge.

However - as can be seen from the explanations in the dialogue Phaidon - the viewing made possible by anamnesis is not a direct perception of the ideas, but only an access to the contents of the memory. It is therefore of far less quality than the immediate, intuitive vision of the separation of the soul from the body and not to be confused with it. The in Phaidon outlined epistemology is pessimistic. It says that the conditions of human existence in principle do not permit a direct, unrestricted perception of ideas. Plato came to a more optimistic assessment in the symposium and in the Politeia . There an idea show seems possible even while the soul is in the body.

In addition to the show, which can be brought about by means of a discursive process, Plato also knows another type of show that has an intuitive and religious character and relates to a transcendent area beyond the world of ideas.

What there are ideas of

There is an idea of ​​every group of individual things present in the world of the senses which bear the same name and thus form a kind. Accordingly, every concept corresponds to an idea. In Plato's dialogues, ideas of inanimate and living beings, of artifacts such as bed and table, of qualities such as warmth, cold and color, of size and smallness, of actions, of movement and rest, of the abstract such as identity, resemblance and Equality, of virtues and geometric figures.

Although the ideas of bed and table are explicitly mentioned in Dialog Politeia and the idea of ​​the weaver's shuttle in Dialog Kratylos , Aristotle denies that Plato actually accepted ideas from artifacts.

In dialogue Parmenides , the philosopher asks Parmenides the young Socrates, if ideas are to accept also regarded as worthless and despicable things such as hair, mud and dirt. Socrates denies this. Parmenides attributes this answer to Socrates' youthful inexperience, which led him to allow himself to be influenced by the usual contempt for such things. Plato adopted ideas not only of the worthless, but also of evils such as the ugly and the unjust. However , he rejected ideas of only negatively delimiting determinations such as “non-Greeks” ( barbaros ) , since these were not species names and the elements of such sets had no common characteristics.


Plato differentiates between mathematical numbers and metaphysical "ideal" (eidetic) numbers. In contrast to mathematical numbers, metaphysical numbers cannot be subjected to arithmetic operations. For example, when it comes to ideal numbers, the two does not mean the number 2, but the essence of duality. The ideal numbers mediate between the one and the unlimited. According to the doctrine of principles, they are to be derived from the principles.

According to Aristotle, Plato attributed a numerical character to the ideas. But this is not to be understood to mean that Plato reduced every idea to a certain number. He assumed a close connection between ideas and ideal numbers, but this is not to be interpreted as a complete ontological identification.

With regard to mathematical objects - the arithmetic and geometrical entities - Aristotle claims that Plato assigned them an intermediate position between ideas and sense objects, because they share immutability with ideas and multiplicity with sense objects. Whether Plato actually assumed an intermediate position between the mathematical entities is disputed in research.

Open questions

The doctrine of ideas raises a multitude of questions that Plato left open in his works. Some of them he ignored, others he discussed but not clarified. The theory of an independent area of ​​ideas led to a number of difficulties and misunderstandings during his lifetime. These are particularly related to the “reification” of abstract structures. Reification is the result of a way of thinking that treats Platonic ideas as contents of sensory perception. It leads to aporias (hopelessness), which Plato himself pointed out in order to show reification as the wrong path.

Plato's criticism of interpretations of the doctrine of ideas, which he considered untenable, has led some researchers to assume that in the last phase of his work he had given up the doctrine of ideas or at least part of its core content because of insoluble contradictions ("revisionism hypothesis"). This view is particularly widespread in English-language research. Its best known proponents include Gilbert Ryle and Gwilym Ellis Lane Owen . The counter-opinion is that he did not consider the difficulties insurmountable or found a variant of the doctrine of ideas that escapes the aporias. Harold Cherniss is one of the determined representatives of this position .

The friends of ideas and the recognizability of the ideas

In Plato's Dialogue Sophistes , an argument with unnamed "friends of ideas" (eidōn phíloi) is conducted. An authority figure, the "stranger from Elea ", reports of a "gigantic battle" between two directions: the materialists , who "pull everything down from heaven and the invisible to earth" and only consider the physical to be, and the "friends of ideas", who defend themselves against materialism "from above downwards from the invisible" and only allow the incorporeal, purely spiritual - the ideas - to be true. The stranger deals critically with both positions.

The question of who the “idea friends” are has long been controversial. The hypothesis that they are megarics is no longer supported in recent research. Three options are still being discussed:

  • that they are Italian Pythagoreans .
  • that it is Plato's students who advocate a variant of the theory of ideas that he disapproves of.
  • that Plato means himself, that is, exercises self-criticism and rejects a version of the theory of ideas previously represented by him. Proponents of this interpretation claim that the concept attributed to the friends of ideas conspicuously coincides with the position taken by Plato in some dialogues such as the Phaedo . The interpretation that Plato means himself, however, does not fit with his statements about the "gigantic fight".

The friends of ideas emphasize a strict separation of being and becoming and refuse to ascribe a being to the changeable. They deny the possibility of life and movement in the realm of true being. Their variant of the doctrine of the separation of the world of ideas is so radical that they come into contradiction if they assert that the ideas are recognizable. The stranger from Elea opposes this concept (“isolationist theory of ideas”) with his moderate position, according to which movement - as well as rest - cannot be denied to beings and life belongs to the purely spiritual realm.

The stranger's criticism of the position of friends of ideas addresses a problem that Plato also grapples with in the Parmenides dialogue : the problem of the separation of the realm of ideas and the world of senses, which in ontology poses the problem of communication, also has an impact on epistemology. In Parmenides the question is discussed whether the ideas are not in principle undetectable because of their separation. This would mean that the Platonic philosophy would have failed and any science in the sense of Plato's understanding of science would be impossible.

The self-predication

In attempting to explain the connection between ideas and things in the sense world, Plato came across other problems which he discussed or at least alluded to in Parmenides . This includes the question of whether a sense object participates in an idea as a whole or only in part of it; both assumptions seem to lead to unacceptable consequences. The most difficult problem is the question of the participation of an idea in itself (“self-predication”). The self-predication (for example the statement “The idea of ​​beauty is itself beautiful”) leads to objections to the doctrine of ideas, which are known as the two “arguments of the third person” (“Third Man Argument”, TMA). The designation "third person" (trítos ánthrōpos) is first attested in Aristotle, but the train of thought is already presented and discussed in Plato's Parmenides .

The starting point of the first argument is the assumption that all elements of a class - for example all people as elements of the human class - are what they are through participation in the idea of ​​this class. If there is an idea “human” that exists separately from the individual human being and gives them the quality of being human, the question arises whether this idea itself also has the characteristic it gives. The question is therefore whether the idea of ​​man belongs to the class of man or whether the idea of ​​the beautiful itself is beautiful. If this question is answered in the negative, the idea is excluded from itself. If it is answered in the affirmative, then it is true for the idea of ​​man as well as for the other elements of this class that an idea is required which gives it the quality of being man. This idea would be the “third person” who would be added to the person as an individual and to the person as an idea. For the third person, another idea would then be required for the same reason, and so on. This would have resulted in an infinite regress . There would be not just one idea of ​​man, but infinitely many.

If one regards the idea as an archetype and the sense objects as its images, a problem of the same type arises. This is the third man's second argument. There is a similarity relationship between the original and the image. Two things are similar because they agree on something that is common to them and connects them. So they are similar in terms of something that is neither the same. Thus, the similarity between archetype and image must also be based on something that is different from them: a common archetype. Again the infinite regress occurs.

In Parmenides the problem of the third man is not solved. It is unknown whether Plato found a solution and whether he stuck to self-predication. All of the proposed solutions discussed in the research literature have strengths and weaknesses, and none are entirely satisfactory.

One possible solution suggested by Gregory Vlastos is known as the "Pauline predication". It refers to a passage in the First Letter to the Corinthians of the apostle Paul , where it is stated: "Love is long-suffering". Grammatically this is a statement about love, but in terms of content about people who love. A distinction must therefore be made between the syntactic and the logical form of the statement; a syntactically self-predicative sentence is not necessarily a true self-predicative sentence. Accordingly, the sentence “Beauty is beautiful” would not be self-predictive either; it would only say that all beautiful things are beautiful.

Peter T. Geach takes a different approach . He suggests viewing ideas neither as properties nor as concepts, but as standards (criteria of assessment). As such, they are objects of a special kind, from which self-predictive statements are possible without absurd consequences.

Another possibility, advocated by Richard S. Bluck and Gail Fine among others, is that the F-being of the idea of ​​F has a different reason than the F-being of the individual things that are F, because they participate in an idea that of is different to them. This hypothesis is a limitation of the validity of the “non-identity assumption” formulated by Vlastos, according to which something can only be F if it participates in an idea of ​​F with which it is not identical. It is not known whether Plato considered such a restriction.

Knut Eming thinks that the self- predication only appears to appear. The impression of self-predication arises because what is meant in the relevant sentences cannot be adequately expressed in a natural, non-formal language: the language itself brings about a reification, which, however, is not in the nature of the thing. Plato's ideas stand against the natural speaking and thinking of both his contemporaries and today's readers.



In antiquity, by far the greatest number of Platonists clung to the theory of ideas. But it was not well received in the other philosophical schools. In particular, the detailed criticism of Aristotle received a lot of attention. Some critics pointed to the problem of self-predication, others made the lack of demonstrability of the doctrine of ideas the starting point of their sometimes mocking attacks.

Opinions in Plato's Academy

Plato's pupil and successor as head ( scholarch ) of the academy, Speusippos , turned completely away from the theory of ideas. He rejected the idea of ​​an independent existence of ideas. Instead of ideas, he put numbers and geometrical figures. He assigned them an independent, independent metaphysical existence as the highest level of being immediately after the One. He viewed them as realities that the human mind could directly grasp, the knowledge of which formed the starting point for all other knowledge.

Xenocrates , the successor of Speusippos, stuck to the concept of ideas, but also took up Speusippos' ideas. He proceeded from a numerically structured totality of the ideas and assigned them numerical character. According to his teaching, numericality must ontologically precede conceptuality, since ideas form a multiplicity, which is only possible through their participation in numbers. Xenocrates accepted ideas only for things of nature; He ruled out ideas from artefacts, since human products, unlike natural things, are not always available. He gave the species ontological priority over the genus. Accordingly, the type of dog, for example, is above the type of animal. The species can exist without the genus, but the genus is omitted if the species are omitted. Xenocrates thereby reversed the hierarchical order in the realm of ideas that Plato had assumed. This step has been described in research as a kind of " Copernican revolution " in Platonism.

The mathematician and philosopher Eudoxus von Knidos , who may have been a member of the academy for a time, advocated an idea that fundamentally contradicted Plato's. He tried to solve the problem of participation with a mixture of theory, assuming that the ideas were mixed with the sense objects. Aristotle compared this with adding a color to what she dyed. Apparently, in contrast to Plato, Eudoxus assumed a spatial presence of ideas in things, but at the same time stuck to the Platonic doctrine of the incorporeal, immutability, archetype, simplicity and separate existence of ideas. Against this variant of the doctrine of ideas, Aristotle raised the charge of inconsistency. The peripatetic Alexander von Aphrodisias handed down peripatetic arguments allegedly originating from Aristotle to refute Eudoxus' doctrine of ideas.

The peripatetic criticism

Aristotle, bust in the Palazzo Altemps , Rome

Aristotle , the founder of the Peripatetic School, dealt intensively with the various variants of the theory of ideas discussed in Plato's Academy and tried to refute them. He formulated his criticism mainly in his now-lost writings On the Ideas and On Philosophy and in his Metaphysics . In his Nicomachean Ethics , he criticized the assumption of an idea of ​​the good and also responded to objections to his argumentation.

Aristotle did not find the evidence for the existence of the ideas convincing. In particular, he asserted that the theory of ideas could not fulfill its purpose of providing an explanation for the existence of sense objects. In Platonism there is an ontological gap between the world of ideas and the world of senses. This is incompatible with the assertion that the world of senses is a product of the world of ideas, because there is nothing that can bridge the gap and explain the assumed influence of ideas on the world of senses (“ Chorismos ” argument). There could be no connection between the two areas because there was no mediating authority. Plato conceived the ideas only as the formal causes of the sense objects and failed to give an effective cause or a purpose cause . In addition, Aristotle considered the reification of independently existing ideas, fatal for the Platonic doctrine of ideas, inevitable. He believed that the apparently general ideas, as separate entities, could not be general, but only a special kind of individual thing. The idea of ​​a separate world of ideas only leads to a hypothetical doubling of the world, which does not contribute anything to the understanding of reality and is therefore unnecessary. The Platonists made category errors because they had not seen that substantiated abstracts such as “the white” were not ousiai (“ substances ”), but qualities, and they had ignored the difference between the first and second ousiai . In addition, ideas that exist separately are considered individual things and not general. Therefore, they are indefinable, because only general things can be defined, and thus also unrecognizable. From the assumption that ideas and individual things are similar, it does not follow that the ideas must be the archetypes of the individual things and that these are copied from them. If the ideas were causal, they would always have to generate continuously, since that which is capable of participation always exists; but the emergence is discontinuous. The idea of ​​participation is not well thought out; it is not a philosophical explanation, but just an empty word, a poetic metaphor , the meaning of which Plato had not investigated. Plato's presentation of his theory of ideal numbers is inadequate, he has not recognized the problems of this theory.

In his commentary on Aristotle's metaphysics, the Aristotelian Aristotelian Alexander von Aphrodisias presented a number of peripatetic arguments against the theory of ideas. For example, he objects to the idea of ​​the same that it cannot be a unitary idea; Rather, there should be several ideas of the same, because the ideal like would have to be like another ideal like in order to be the same at all.

Middle Platonism

With the Middle Platonists , cosmology was the focus of interest. The philosophers viewed the conception of ideas primarily from a cosmological point of view and connected them with their ideas of divine rule in the cosmos. They differentiated between the highest, absolutely transcendent deity, who has no direct relationship to the sensually perceptible world, and the creator god, the demiurge , subordinate to it . The Creator God was considered the active cause of the sense objects, in the ideas one saw the paradigmatic (archetypal) cause, in the matter the material cause . This is known in research as the Middle Platonic "three principles teaching".

Despite being embedded in comprehensive, complex cosmological and theological concepts, the theory of ideas did not lose its importance among the Middle Platonists. It was considered a central component of Platonism and was defended against criticism from other schools of philosophy.

The question of where the ideas are and how they relate to the deity was answered differently. Opinions differed as to whether they are to be located in the divine nous or outside of it. Mostly they were viewed as thoughts of the absolutely transcendent God or the Creator God. The Middle Platonists were under the influence of the theology of Aristotle, according to which God thinks himself and this is his only activity. But there was also the view that the ideas had an independent existence independent of the divine intellect . The problem of mediating between the purely spiritual and the material gave rise to the distinction between transcendent ideas as divine thoughts and immanent ideas in the sensory world, which mediate between the transcendent ideas and the material realm.

The Middle Platonist Alcinous gave a definition of the idea in his influential textbook Didaskalikos : “The idea is his thinking with regard to God, the first object of thought with regard to us, measure with regard to matter, with regard to the sensually perceptible cosmos pattern, Ousia considered in terms of himself. ”Furthermore, from the statements of Alcinous, who presumably lived in the 2nd century, it emerges that the majority of the Middle Platonists were of the opinion that there were only ideas that were natural. Ideas of artefacts, of things contrary to nature like diseases, of individual individuals, of worthless things like dirt, and of relations like "greater" were considered impossible because the ideas were considered perfect and divine.

The Jewish thinker Philo of Alexandria , who was strongly influenced by Platonism, followed the Middle Platonic model. He identified the "cosmos of ideas", which is the first image of God, with God's reason, the divine Logos . The logos is the imagined world, according to whose "highly god-like" model God created the visible world. In this way, Philon's ideas take on the role of mediating authority between the transcendent God and the created world.


Plotinus , the founder of Neoplatonism , and the later Neoplatonists who developed his ontological model, adopted a three-part basic structure of the spiritual world with three hierarchically ordered principles: At the top is the absolutely transcendent " One ", below the supra-individual spirit or intellect ( Nous ) , followed by the spiritual area.

According to Neoplatonic doctrine, the nous is the world of pure thought. He thinks exclusively of himself, that is, his contents: the objects of pure thought in their entirety. The nous consists of nothing other than the totality of the Platonic ideas and is their only ontological place. This position is expressed in the famous theorem Ideas exist only within the nous , which sums up the core of Plotin's doctrine of ideas. The ideas are not parts of the nous in analogy to a spatial object composed of parts, but each individual idea is the nous as an individual, that is, it contains the whole nous and thus all other ideas in itself. This means that all ideas interpenetrate one another; they are not separated, but without losing their particular peculiarity.

In post-Plotinic Neo-Platonism - as in Middle Platonism - a distinction was made between transcendent ideas and ideas as immanent forms of sense objects. Since a participation of material objects in the transcendent ideas was considered impossible, the participation of the sensory things in the ideas was related to the immanent forms. The philosophers of the late ancient Neo-Platonism movement founded by Iamblichos believed that there were no ideas of artifacts, things contrary to nature, evils and individuals.

The set of ideas was usually considered finite. A minority position was represented by Amelios Gentilianos , a student of Plotinus who considered their number to be infinite, thus allowing the principle of numerical infinity in the intelligible world.

The Neo-Platonist Syrianos († around 437) thoroughly dealt with Aristotle's criticism of the theory of ideas. He tried to refute them by breaking them down into ten arguments and going into each one individually.

Only in the 6th century - with Simplikios and the Christian philosopher Johannes Philoponos - is a terminological identification of the Platonic ideas attested by assigning them to their originator in the sense of today's linguistic usage ("Plato's ideas", "Ideas after Plato").

Church fathers

In Christian literature, the doctrine of ideas was usually rejected, ignored, ridiculed or at least viewed as a distanced one until the turn of the 2nd and 3rd centuries. Then a rethink began; Attempts began to integrate a concept of ideas into the Christian worldview. The first was Clement of Alexandria . The model developed by Philon of Alexandria provided the impetus.

For the ancient church fathers, who accepted a form of the doctrine of ideas, it was clear that the ideas did not exist independently of God, but were his products. It was assumed that he produced them in his mind before the visible world, or that they were present in the divine spirit regardless of time. Among the Christian proponents of the doctrine of ideas the idea was widespread that it was not a matter of a discovery by Plato. Although the doctrine was not known by name, it was known in substance before the Greek philosopher. The original preacher of the truth contained in Platonism was Moses , to whom Plato owed his knowledge. The Platonic thought that knowledge of ideas is possible, but presupposes a purification of the soul and its turning away from the world of the senses, was well received in Christian circles.

The church father Augustine developed a Christian doctrine of ideas, taking over the main features of the Platonic concept including the idea of ​​participation. He said that ideas are the reasons (rationes) of things that exist beyond space and time . Everything that arises and passes away is designed according to their pattern and receives from them the totality of its characteristics. Their place is the divine reason (divina intelligentia) . With this positioning of the ideas, Augustine adopted a Middle Platonic model, which he reinterpreted as Christian by combining it with the doctrine of the Trinity . He identified the divine reason in which the ideas were contained as the Word of God made flesh , Jesus Christ . The word of God is the unshaped form of all shaped things. At the same time it is also a statement of God about himself. In his word - and thus also in ideas - God knows himself. Augustine also understood human knowledge as knowledge of ideas. Knowledge is based on the knowledge of ideas, without it one cannot acquire wisdom. The human knowledge of ideas is possible through participation (participatio) in the word of God. The unchangeable truths to which man thereby gains access are inherent in himself and not derived from sensory perception. Sensory perception only points out the knowledge that is already latent in him, so that he becomes aware of it.

middle Ages

In the Middle Ages, the reception of the Platonic doctrine of ideas took place predominantly through late antique writers, whose idea concepts were influenced by the Middle and Neoplatonic. The classification of ideas in systematic representations of philosophical-theological models did not begin on a larger scale until the 13th century.

Basics of reception

Among the late antique authors to whom the Latin-speaking medieval scholars owed their knowledge of the Platonic doctrine of ideas, Augustine, Calcidius and Boethius were the most influential.

Augustine created the prerequisites for the concept of “idea” to be taken up by medieval thinkers in the context of the reception of the Platonic ontology and for this concept to have a strong content and terminological effect. Calcidius, who partially translated Plato's Timaeus into Latin and wrote a commentary on this dialogue, gave medieval posterity direct access to an important source. Boethius addressed the doctrine of ideas in his writings “ The Consolation of Philosophy ” and “How the Trinity is one God and not three Gods” (in short “About the Trinity”). He also translated the isagogue of the Neo-Platonist Porphyrios , an introduction to Aristotelian logic, into Latin. The foreword to the Isagogue contains the three questions that became the starting point of the discussions about the doctrine of ideas in the Middle Ages: whether species and genera exist as independent reality or only as products of thought, whether their independent existence is to be understood as physical or incorporeal, and whether they are tied to the objects of sense perception or exist independently of them.

In the Middle Ages, the determination of ideas as timeless archetypes ("forms") that existed in the spirit of God and according to whose patterns he created the sense objects, achieved a lasting effect in the Middle Ages.


Representation of Eriugenas in the manuscript Paris, Bibliothèque Nationale, Lat. 6734

In the 9th century, the Irish philosopher Eriugena , who was strongly influenced by Neoplatonism, orientated himself on the ideas of the late ancient theologian Pseudo-Dionysius Areopagita , an important mediator of Neoplatonic ideas. Pseudo-Dionysius was held in high esteem in the Middle Ages because he was considered a direct disciple of the Apostle Paul . Following on from the teachings of Pseudo-Dionysius, Eriugena arrived at his conception of ideas, in which the ideas have the function of "initial reasons" (primordiales causae) . He distinguished between God as the creative and itself uncreated nature, ideas as the creative and created nature, and the sense objects as the created and non-creating nature. According to Eriugena's teaching, God created the ideas so that they in turn create what is below them as the starting points: both the spiritual and heavenly beings as well as the whole world that is perceptible to the senses. In this way, the ideas are assigned the mediation between God and all of creation. Since Eriugena held the ideas forever, he did not see their creation as a temporal process, but only meant with this concept that they did not have their being from themselves, but from God. He only considered the existence and meaning of the ideas, not their being in themselves, to be recognizable. He interpreted future redemption as the return of all that was created to its foundations and through them in God.

High Middle Ages

In the High Middle Ages , the group of philosophers known as the “ School of Chartres ” received Plato's Timaeus intensely. For these scholars, the Timaeus was the basic text for the philosophical understanding of the cosmological subject area. Probably already Bernhard von Chartres († after 1124), who played a key role in the development of the School of Chartres, assumed a triad God - ideas - matter in the doctrine of creation and cosmology, the originator of which was Plato.

Bernhard introduced the concept of "forms of origin" (formae nativae) into medieval Platonism . This is how he referred to forms that he regarded as an actively mediating principle between the world of ideas and matter. According to his teaching, the forms of creation are images of unchangeable ideas. In principle, eternal ideas cannot enter into any connection with matter, but only have an indirect effect on them via the forms of origin that are suitable for matter. In contrast to the ideas, the forms of development are changeable. By being absorbed by matter, they enable the creation of all concrete individual things and give them their species-specific properties. With this doctrine, Bernhard took up the distinction of ancient Neoplatonists between the transcendent ideas and the ideas as immanent forms of the sense objects.

The thinkers of his school took up Bernhard's Platonism. John of Salisbury called the forms of origin "additional forms" (advenientes formae) , since they add to matter. Wilhelm von Conches taught that God created the world according to a pattern, the “archetypal world” (mundis archetypus) . Wilhelm called this pattern a “summary of ideas” (collectio idearum) and equated it with the divine spirit. Thierry von Chartres understood ideas to be the nature of things as they are in themselves.

Wilhelm von Auvergne assumed an archetypal world, but rejected the view that the truth with regard to the sense objects is to be found there and not in the images and therefore the sense world is an illusory world. He meant that earthly fire and not the idea of ​​fire is the "true" fire. For this he put forward a number of arguments, including the idea that properties such as spatiality, which are absent in the archetypal world, belong to the truth of sense objects.

Late Middle Ages

In the 13th century the scholars' engagement with the theory of ideas intensified. The criticism of Aristotle, which came into focus with the increased reception of Aristotle at this time, provided an important impetus for this. A trend that continued to be based on the ideas of Augustine, the most famous representative of which was the Franciscan Bonaventure († 1274), was opposed by increasingly strong currents in the late Middle Ages that more or less radically opposed the basic assumptions of Platonism.

As a leading exponent of late medieval Aristotelianism , Thomas Aquinas († 1274) accepted ideas as principles of creation in the spirit of the Creator God, but did not take into account that the ideas in the process of creation were their own causality. Rather, he meant that ideas could only exercise their function as the form causes of created things on the basis of acts of will of God, that God's will is always required as an effective cause . Thomas agreed with Aristotle's criticism of Plato's concept and, in particular, rejected the participation of the created in the divine ideas. He rejected Plato's doctrine of "separate ideas that are by themselves", referring to Aristotle. He considered the assumption of the existence and the multitude of ideas to be necessary.

Thomas Aquinas taught that there are ideas not only of species but also of individuals. This conviction also prevailed in the direction founded by Johannes Duns Scotus († 1308), Scotism .

The nominalists or conceptualists of the sign theory made a complete break with the Platonic tradition . In the “ Universalienstreit ” they fought against conceptual realism (universal realism, also called “realism” for short), the theory of the reality of universals (general concepts). Conceptual realists were not only the representatives of the conventional Platonic-Augustinian way of thinking, but also the Aristotelian-thinking Thomists (followers of the teachings of Thomas Aquinas) and the Scotists. They all agreed on the assumption that the general terms denote something objectively real, be it in the Platonic sense of ontological entities or in the Aristotelian sense of forms as givens in the sense objects. These positions opposed the view of the nominalists or conceptualists. According to their teaching, the general terms are only “names” (nomina) , that is, signs that the human mind needs for its activity. Accordingly, the general has a subjective, purely mental reality in thought and only there. It has no ontological relevance. Wilhelm von Ockham , the spokesman for nominalism based on the theory of signs in the 14th century, denied that ideas had their own reality in the spirit of God. For him, the term “idea” did not refer to any extramental givenness, but referred exclusively to the fact that a certain object of knowledge was known.

Islamic world

Among medieval scholars who wrote in Arabic, the Platonic ideas were known as ṣuwar aflāṭūniyya ("Platonic forms") or muthul aflāṭūniyya ("Platonic archetypes"). From the first half of the 10th century, the name ṣuwar aflāṭūniyya is attested; the expression muthul aflāṭūniyya may have been coined by ibn Sīnā in the 11th century . This is the only case of medieval Arabic concept formation to designate a philosophical concept with reference to its ancient originator.

The Arabic-writing scholars who dealt with the problematic of ideas apparently had no access to full translations of Platonic dialogues. They drew their knowledge from Neoplatonic literature, from the metaphysics of Aristotle and from doxographic reports. The influential philosopher al-Farabi , who was active in the first half of the 10th century, vacillated between the Aristotelian rejection of transcendent forms and the Neoplatonic ontology. In the Rasā'il ikhwān aṣ-ṣafā ' , an encyclopedic work of the 10th century, a variant of the doctrine of ideas is represented in which "luminous" spiritual forms have the function of archetypes of all sensory objects. These forms are perceptible to the soul when it reaches an out-of-body state. In the 11th century, the Iranian thinker ibn Sīnā dealt intensively with the Platonic doctrine of ideas and finally came to a negative position.

Early modern age

Among the Renaissance humanists , the Platonic-oriented direction, of which Marsilio Ficino was the most famous representative in the 15th century , followed the traditional guidelines of a neo-Platonic ontology including the theory of ideas. Even in Jesuit circles, which followed the tradition of medieval scholasticism, late medieval ontological ideas remained present in the early modern period . In the new currents that dominated the philosophical discourse of the 17th and 18th centuries, such concepts no longer played a role. The term “idea” was re-shaped by René Descartes (1596–1650), who rejected the assumption of a world of ideas in the divine intellect. It was given a meaning only related to the human spirit. In the following years it was usually used in an unplatonic sense to denote the content of consciousness. Ideas as ontological entities in the Platonic sense were considered obsolete. Immanuel Kant , too , gave the ideas no ontological significance. In his opinion, "Plato left the world of the senses because it sets so narrow barriers to the understanding, and ventured beyond it, on the wings of ideas, into the empty space of the pure understanding." In this, Plato is like a dove who thinks it can fly even better in a vacuum than in the air, the resistance of which it feels. He did not notice "that he did not gain a path through his efforts". This is the common mistake of those who erect a speculative building without first investigating "whether the reason for it was well laid".


In the modern age, ideas play an essential role for a number of philosophers in the context of ontological, epistemological or ethical concepts. The term "idea" is used in different meanings. In some thinkers traces of the ontological tradition of Platonism can be seen. But Plato's theory of ideas has hardly appeared as an important source of inspiration. Often any ontological relevance of ideas is denied.

Georg Wilhelm Friedrich Hegel said that "platonic abstraction" could "no longer suffice for us (...)". According to Hegel, the idea of ​​the beautiful must be grasped more deeply and more concretely, “because the lack of content that sticks to the Platonic idea no longer satisfies the richer philosophical needs of our present-day mind”.

In the 19th century, Friedrich Nietzsche emerged as a sharp critic of the Platonic doctrine of ideas. He fought them as part of his polemics against Platonism. In his Götzen-Twilight he wrote that the history of the doctrine of ideas was the story of an error, the alleged "true world" of ideas had turned out to be a fable; it is "an unnecessary idea, an idea that has become superfluous, consequently a refuted idea".

Martin Heidegger believed that Plato had succumbed to the danger of reification of ideas and thus gave the course of the history of Western philosophy a fateful turn. He rejected the Platonic assumption of a static being, which, as the “whatness” of being, defines its essence and which is always there before the respective being and survives it. From Heidegger's point of view, being is not subordinate to being or a Platonic idea.

Different directions have emerged among the philosophical historians concerned with the interpretation of Plato's theory. While the "Unitarians" think that Plato consistently represented a doctrine with essentially constant basic features, the "revisionists" emphasize presumed differences between development phases and consider the assumption of a serious change in position to be inevitable. While the strong revisionism assumes a radical break, "evolutionists" only expect modifications of the doctrine. In addition, there are two main directions as to what is meant by Platonic ideas. One direction conceives the doctrine of ideas primarily as an ontological theory of ideas as real entities. The other direction (“analytical school”) looks at ideas from a formal point of view, interprets them as predicates and order categories of the mind and sees the essentials in the methodological, epistemological and logical meaning of Plato's theory. The study of Plato's theory of ideas by the neo-Kantian Paul Natorp , published in 1903, played a pioneering role in the non-ontological interpretation .

Another controversial issue is the extent to which it is legitimate to reconstruct a unified theory of Plato from the statements of the dialogue figures about ideas. Some researchers deny that the "classical" doctrine of ideas presented in modern manuals on the history of philosophy corresponds to the actual conception of the ancient thinker, and do not believe that he worked his considerations into a coherent theory.


  • Gail Fine: On Ideas. Aristotle's Criticism of Plato's Theory of Forms . Clarendon Press, Oxford 1993, ISBN 0-19-823949-1 (critical edition, English translation and thorough investigation)
  • Hans-Georg Gadamer : Plato: Texts on the theory of ideas . 2nd edition, Vittorio Klostermann, Frankfurt am Main 1986, ISBN 3-465-01696-3 (Greek text based on the edition by John Burnet with translation and explanations)


Overview representations in manuals

Introductions and investigations

Plato and Aristotle

  • Knut Eming: The escape into thinking. The beginnings of the Platonic philosophy of ideas . Meiner, Hamburg 1993, ISBN 3-7873-1012-6
  • Andreas Graeser : Plato's theory of ideas. Language, logic and metaphysics. An introduction . Paul Haupt, Bern 1975, ISBN 3-258-01168-0
  • Wilfried Kühn: Introduction to Metaphysics: Plato and Aristotle. Meiner, Hamburg 2017, ISBN 978-3-7873-3006-5 , pp. 23–96
  • Gottfried Martin : Plato's theory of ideas . De Gruyter, Berlin 1973, ISBN 3-11-004135-9
  • Richard Patterson: Image and Reality in Plato's Metaphysics. Hackett, Indianapolis 1985, ISBN 0-915145-73-1
  • Gyburg Radke : Plato's theory of ideas . In: Franz Gniffke, Norbert Herold (Hrsg.): Classical questions in the history of philosophy I: Antiquity to Renaissance . Lit Verlag, Münster 2002, ISBN 3-8258-2769-0 , pp. 17-64
  • Gilbert Ryle : Plato's Progress . Cambridge University Press, London 1966 (standard representation of the revisionist view)
  • Hermann Schmitz : The theory of ideas of Aristotle , Volume 2: Plato and Aristotle . Bouvier, Bonn 1985, ISBN 3-416-01812-5 (stimulating work; contains numerous hypotheses that deviate from prevailing doctrines)

middle Ages

  • Alain de Libera: The universal dispute. From Plato to the end of the Middle Ages . Wilhelm Fink, Munich 2005, ISBN 3-7705-3727-0
  • Rüdiger Arnzen : Platonic Ideas in Arabic Philosophy. Texts and materials on the conceptual history of ṣuwar aflāṭūniyya and muthul aflāṭūniyya. De Gruyter, Berlin 2011, ISBN 978-3-11-025981-0

Philosophy Bibliography : Theory of Ideas - Additional references to the topic

Web links

Wiktionary: Theory of ideas  - explanations of meanings, word origins, synonyms, translations


  1. See Christian Schäfer's terminology : Idea / Form / Shape / Essence . In: Christian Schäfer (Ed.): Platon-Lexikon , Darmstadt 2007, pp. 157–165, here: 157; Michael Erler: Platon (= Hellmut Flashar (Hrsg.): Outline of the history of philosophy. The philosophy of antiquity , volume 2/2), Basel 2007, p. 391f.
  2. On Plato's use of these terms see the thorough investigation by Geert Roskam et al: Plato . In: André Motte et al. (Ed.): Philosophy de la Forme. EIDOS, IDEA, MORPHÈ dans la philosophie grecque des origines à Aristote , Louvain-la-Neuve 2003, pp. 65–330.
  3. For etymology see Pierre Chantraine : Dictionnaire étymologique de la langue grecque. Histoire des mots , Paris 2009, p. 438; Hjalmar Frisk : Greek etymological dictionary , Volume 1, Heidelberg 1960, p. 708.
  4. Christian Schäfer: Idea / Form / Shape / Essence . In: Christian Schäfer (Ed.): Platon-Lexikon , Darmstadt 2007, pp. 157–165, here: 159–161.
  5. See Hans Diller : On the use of εἶδος and ἰδέα in pre-Platonic times . In: Hans-Heinz Eulner et al. (Ed.): Medical history in our time , Stuttgart 1971, pp. 23-30. Wilhelm Pape : Greek-German Concise Dictionary , 3rd Edition, Volume 1, Reprint Graz 1954, p. 1235, and Henry George Liddell , Robert Scott : A Greek-English Lexicon , 9th Edition, Oxford 1996, provide numerous examples of the ancient use of idea , P. 817.
  6. Christof Rapp , Tim Wagner: eidos / Gestalt, Art, Form . In: Otfried Höffe (Hrsg.): Aristoteles-Lexikon (= Kröner's pocket edition . Volume 459). Kröner, Stuttgart 2005, ISBN 3-520-45901-9 , pp. 147-158; Michael Bordt : eidos . In: Christoph Horn, Christof Rapp (ed.): Dictionary of ancient philosophy , Munich 2002, pp. 119–122, here: 120.
  7. Evidence in the Thesaurus linguae Latinae , Volume 7/1, Leipzig 1964, Col. 178f. See Helmut Meinhardt: Idea. I. Antiquity . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 55–65, here: 55.
  8. Seneca, Epistulae morales 58, 26.
  9. On the terminology of Calcidius see Gangolf Schrimpf et al.: Idea. II. Middle Ages . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 65-102, here: 65f.
  10. ^ Augustine, De diversis quaestionibus 46.
  11. Gangolf Schrimpf offers numerous examples of the medieval history of concepts: Idea. II. Middle Ages . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 65-102.
  12. ^ Andreas Graeser: Platon's theory of ideas , Bern 1975, p. 14.
  13. For this context of Platonic philosophy see Michael Erler: Platon (= Hellmut Flashar (Hrsg.): Grundriss der Geschichte der Philosophie. Die Philosophie der Antike , Volume 2/2), Basel 2007, pp. 338 f., 343 f. , 393.
  14. See also Rafael Ferber: Plato's idea of ​​the good , 2nd edition, Sankt Augustin 1989, pp. 39–48; Michael Erler: Platon (= Hellmut Flashar (Hrsg.): Outline of the history of philosophy. The philosophy of antiquity , Volume 2/2), Basel 2007, p. 393.
  15. Charles H. Kahn advocates late dating: Plato and the Socratic Dialogue , Cambridge 1996, pp. 92–95.
  16. See also Michael Erler: Platon (= Hellmut Flashar (Hrsg.): Grundriss der Geschichte der Philosophie. Die Philosophie der Antike , Volume 2/2), Basel 2007, p. 393; Charles H. Kahn: Plato and the Socratic Dialogue , Cambridge 1996, pp. 354f.
  17. ^ Reginald E. Allen : Plato's 'Euthyphro' and the Earlier Theory of Forms , London 1970, pp. 163f.
  18. ^ Rafael Ferber: Plato's idea of ​​the good , 2nd edition, Sankt Augustin 1989, p. 38f.
  19. Plato, Politeia 510c – 511d. See also Wolfgang Wieland : Platon und die Formen des Wissens , 2nd, extended edition, Göttingen 1999, pp. 207–217; Jürgen Mittelstraß : The dialectic and its scientific preparatory exercises (Book VI 510b – 511e and Book VII 521c – 539d). In: Otfried Höffe (Ed.): Platon: Politeia , 3rd edition, Berlin 2011, pp. 175–191, here: 182–186.
  20. See on this understanding of mathematics Konrad Gaiser : Plato's overview of the mathematical sciences . In: Konrad Gaiser: Collected Writings , Sankt Augustin 2004, pp. 137–176; Michael Erler: Platon (= Hellmut Flashar (Hrsg.): Outline of the history of philosophy. The philosophy of antiquity , Volume 2/2), Basel 2007, p. 515f.
  21. See Matthias Baltes: Idea (doctrine of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 214–216; Michael Erler: Platon (= Hellmut Flashar (ed.): Outline of the history of philosophy. The philosophy of antiquity , Volume 2/2), Basel 2007, pp. 395–398, 456–458; Giovanni Reale: On a new interpretation of Plato , Paderborn 1993, pp. 159–177.
  22. Plato, Sophist 218e-221b.
  23. Plato, Sophist 252e-253c.
  24. Plato, Sophistes 254b-255e.
  25. See on the hierarchical structure Giovanni Reale: On a new interpretation of Plato , Paderborn 1993, pp. 184–195; Helmut Meinhardt: Teilhabe bei Platon , Freiburg 1968, pp. 27–87.
  26. ^ Matthias Baltes: Idea (theory of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 216; Franz von Kutschera : Plato's Philosophy , Volume 3, Paderborn 2002, p. 196f .; Michael Schramm: Diheresis / Dihairesis . In: Christian Schäfer (Ed.): Platon-Lexikon , Darmstadt 2007, pp. 92–95; Michael Hoffmann: The emergence of order , Stuttgart 1996, pp. 95–110, 121–133.
  27. For the community of ideas see Jens Halfwassen : The rise to one. Studies on Plato and Plotinus , 2nd edition, Leipzig 2006, p. 240f .; Hermann Schmitz: The theory of ideas of Aristoteles , Vol. 2: Platon and Aristoteles , Bonn 1985, pp. 69-79, 89-92.
  28. A summary of relevant statements by Plato is offered by Thomas Alexander Szlezák : The idea of ​​the good in Plato's Politeia , Sankt Augustin 2003, p. 111f. Michael Erler offers an overview of the extensive research literature : Platon (= Hellmut Flashar (ed.): Grundriss der Geschichte der Philosophie. Die Philosophie der Antike , Volume 2/2), Basel 2007, pp. 402–404.
  29. Hans Joachim Krämer : Arete in Platon and Aristoteles , Heidelberg 1959, pp. 127-135.
  30. Rafael Ferber provides an overview: Isn't the idea of ​​the good transcendent or is it? Again Plato's ΕΠΕΚΕΙΝΑ ΤΗΣ ΟΥΣΙΑΣ . In: Damir Barbarić (ed.): Plato about the good and justice , Würzburg 2005, pp. 149–174, here: 149–156.
  31. Greek presbeía " priority of age", also translated as "dignity".
  32. Plato, Politeia 509b.
  33. Thomas Alexander Szlezák provides a summary of this position: The idea of ​​the good in Plato's Politeia , Sankt Augustin 2003, p. 67f. Cf. the argumentation of Rafael Ferber: Isn't the idea of ​​the good transcendent or is it? Again Plato's ΕΠΕΚΕΙΝΑ ΤΗΣ ΟΥΣΙΑΣ . In: Damir Barbarić (ed.): Plato on the good and justice , Würzburg 2005, pp. 149–174, here: 154–160 and Giovanni Reale: To a new interpretation of Plato , Paderborn 1993, pp. 275–281.
  34. The transcendence of being of the idea of ​​the good is rejected by, among others, Theodor Ebert : Opinion and knowledge in Plato's philosophy , Berlin 1974, pp. 169–173, Matthias Baltes: Is the Idea of ​​the Good in Plato's Republic Beyond Being? In: Matthias Baltes: Dianoemata. Small writings on Plato and Platonism , Stuttgart 1999, pp. 351–371 and Luc Brisson : L'approche traditional de Plato par HF Cherniss . In: Giovanni Reale, Samuel Scolnicov (eds.): New Images of Plato , Sankt Augustin 2002, pp. 85–97.
  35. Plato, Politeia 518c and 526E. Thomas Alexander Szlezák argues against the evidential value of these passages as an argument against the transcendence of being: The idea of ​​the good in Plato's Politeia , Sankt Augustin 2003, p. 66.
  36. The sources are compiled by Marie-Dominique Richard: L'enseignement oral de Platon , Paris 1986, pp. 243–381; Michael Erler: Platon (= Hellmut Flashar (Hrsg.): Grundriss der Geschichte der Philosophie. Die Philosophie der Antike , Volume 2/2), Basel 2007, pp. 406–429 and provides overviews of the sources, the research literature and the course of the discussion Franco Ferrari: Les doctrines non écrites . In: Richard Goulet (Ed.): Dictionnaire des philosophes antiques , Volume 5, Part 1 (= V a), Paris 2012, pp. 648–661.
  37. Plato, Philebos 23b – 27c; see the commentary by Dorothea Frede : Plato: Philebos. Translation and Commentary , Göttingen 1997, pp. 184–211 and Giovanni Reale: To a new interpretation of Plato , Paderborn 1993, pp. 413–444 and Eugenio E. Benitez: Forms in Plato's Philebus , Assen 1989, pp. 59–91.
  38. Michael Erler: Platon , Munich 2006, pp. 162f.
  39. To equate the one with the good, see Jens Halfwassen: The rise to one. Investigations on Plato and Plotinus , 2nd edition, Leipzig 2006, pp. 21–23 and p. 221, note 4; Thomas Alexander Szlezák: The idea of ​​the good in Plato's Politeia , Sankt Augustin 2003, p. 70f .; Hans Joachim Krämer: ἘΠΕΚΕΙΝΑ ΤΗΣ ΟΥΣΙΑΣ. Plato, Politeia 509 B . In: Archive for the history of philosophy 51, 1969, pp. 1–30; Hans Joachim Krämer: Arete in Platon and Aristoteles , Heidelberg 1959, pp. 138, 324, 456, 473–476, 548. Rafael Ferber argues against the equation: Plato's idea of ​​the good , 2nd edition, Sankt Augustin 1989, p. 76 -78.
  40. ^ Tilman Borsche : The necessity of ideas: Politeia. In: Theo Kobusch , Burkhard Mojsisch (Ed.): Platon. His dialogues in the perspective of new research , Darmstadt 1996, pp. 96–114, here: 108.
  41. An overview of Plato's idea of ​​participation is provided by Veronika Roth and Christian Schäfer: Teilhabe / Participation . In: Christian Schäfer (Ed.): Platon-Lexikon , Darmstadt 2007, pp. 277–282.
  42. ^ Helmut Meinhardt: Teilhabe bei Platon , Freiburg 1968, pp. 89–94; Gyburg Radke: Plato's theory of ideas . In: Franz Gniffke, Norbert Herold (Hrsg.): Classical questions in the history of philosophy I: Antiquity to Renaissance , Münster 2002, pp. 17–64, here: 55–60.
  43. On Plato's use of the term, see Nario Fujisawa: Ἔχειν, Μετέχειν, and Idioms of 'Paradeigmatism' in Plato's Theory of Forms . In: Phronesis 18, 1973, pp. 30-58; Michael Erler: Platon (= Hellmut Flashar (Hrsg.): Outline of the history of philosophy. The philosophy of antiquity , volume 2/2), Basel 2007, p. 397f.
  44. Detlef Thiel: The Philosophy of Xenokrates in the Context of the Old Academy , Munich 2006, pp. 197–208; Hans Joachim Krämer: Der Ursprung der Geistmetaphysik , 2nd edition, Amsterdam 1967, pp. 329–334; Christina Schefer: Plato's unspeakable experience , Basel 2001, pp. 57–60.
  45. Jens Halfwassen provides an overview of the problem: Monism and dualism in Plato's doctrine of principles . In: Thomas Alexander Szlezák (Ed.): Platonisches Philosophieren , Hildesheim 2001, pp. 67–85. Cf. Michael Erler: Platon (= Hellmut Flashar (Hrsg.): Grundriss der Geschichte der Philosophie. Die Philosophie der Antike , Volume 2/2), Basel 2007, p. 428f.
  46. Benedikt Strobel provides an overview of various hypotheses on the question of the two-worlds theory: Two-worlds theory . In: Christoph Horn et al. (Ed.): Platon-Handbuch , Stuttgart 2009, pp. 358–362.
  47. Rafael Ferber: Plato's idea of ​​the good , 2nd edition, Sankt Augustin 1989, pp. 19–48; Michael Erler: Platon ( Outline of the history of philosophy. The philosophy of antiquity , edited by Hellmut Flashar, Volume 2/2), Basel 2007, pp. 390, 393; Giovanni Reale: On a new interpretation of Plato , Paderborn 1993, pp. 178-184.
  48. ^ Theodor Ebert: Opinion and knowledge in Plato's philosophy , Berlin 1974, pp. 181–193.
  49. John N. Findlay: Plato: The Written and Unwritten Doctrines , London 1974, pp. XI f., 32-40.
  50. Christoph Quarch: Sein und Seele , Münster 1998, pp. 132–149.
  51. Richard L. Nettleship: Lectures on the Republic of Plato , London 1963 (reprint; first published 1897), pp. 238-240.
  52. Michael Erler: Platon , Munich 2006, p. 148f.
  53. ^ Matthias Baltes: Idea (theory of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 219; Jan Szaif: Plato's Concept of Truth , Freiburg 1996, pp. 110–132.
  54. On Plato's doctrine of the soul and the migration of souls, see the overview by Michael Erler: Platon ( Grundriss der Geschichte der Philosophie. Die Philosophie der Antike , edited by Hellmut Flashar, Volume 2/2), Basel 2007, pp. 375-390 and Jörn Müller : Transmigration of souls . In: Christoph Horn et al. (Ed.): Platon-Handbuch , Stuttgart 2009, pp. 324–328.
  55. Tópos hyperouránios according to Plato, Phaedrus 247c.
  56. Oikeía Episteme , according to Plato, Phaedo 75e.
  57. Plato, Menon 81c – d, Phaedo 72e – 77a.
  58. Peter Stemmer : Plato's Dialectic. The early and middle dialogues , Berlin 1992, p. 244f .; Michael Erler: Platon ( Outline of the history of philosophy. The philosophy of antiquity , edited by Hellmut Flashar, Volume 2/2), Basel 2007, p. 365f .; Jan Szaif: Plato's Concept of Truth , Freiburg 1996, pp. 168–182.
  59. Plato, Politeia 533c – d.
  60. Ludwig CH Chen: Acquiring Knowledge of the Ideas , Stuttgart 1992, pp. 13-17, 26-28, 34-36, 53-56, 167-173, 183-190.
  61. Christina Schefer: Plato's untold experience. Another approach to Plato , Basel 2001, pp. 25ff., 223–225.
  62. Plato, Politeia 596a-b, Kratylos 389a-b.
  63. Aristotle, Metaphysics 1070a18. For interpretation, see David Ross : Plato's Theory of Ideas , Oxford 1951, pp. 171-175. Cf. Giovanni Reale: On a new interpretation of Plato , Paderborn 1993, p. 410f.
  64. Plato, Parmenides 130c – e. See Christoph Ziermann: Platon's negative dialectic , Würzburg 2004, pp. 40–43.
  65. Plato, Politeia 475e-476a.
  66. Plato, Politicus 262c-263a.
  67. ^ Giovanni Reale: On a new interpretation of Plato , Paderborn 1993, pp. 211, 219-221.
  68. ^ Detlef Thiel: The Philosophy of Xenokrates in the Context of the Old Academy , Munich 2006, pp. 209–225.
  69. ^ Giovanni Reale: On a new interpretation of Plato , Paderborn 1993, pp. 214–221; David Ross: Plato's Theory of Ideas , Oxford 1951, pp. 216-220. Cf. Rafael Ferber: Plato's idea of ​​the good , 2nd edition, Sankt Augustin 1989, pp. 162–189.
  70. Aristotle, Metaphysics 987b.
  71. See Giovanni Reale: To a new interpretation of Plato , Paderborn 1993, p. 218f .; Rafael Ferber: Plato's idea of ​​the good , 2nd edition, Sankt Augustin 1989, pp. 186-189; Julia Annas : On the “Intermediates” . In: Archive for the history of philosophy 57, 1975, pp. 146–166.
  72. ^ Matthias Baltes: Idea (theory of ideas). In: Real Lexicon for Antiquity and Christianity. Volume 17, Stuttgart 1996, Col. 213-246, here: 220 f.
  73. ^ Andreas Graeser: Platons Parmenides , Stuttgart 2003, pp. 5–8; Giovanni Reale: On a new interpretation of Plato , Paderborn 1993, p. 303; Hans Joachim Krämer: Aristotle and the academic doctrine of the Eidos . In: Archive for the History of Philosophy 55, 1973, pp. 119–190, here: 126.
  74. Andreas Graeser: Platons Parmenides , Stuttgart 2003, p. 75 and note 111. For a consistent adherence to Plato's theory of ideas, among others, Giovanni Reale: To a new interpretation of Plato , Paderborn 1993, p. 298-313 and Eugenio E. Benitez plead : Forms in Plato's Philebus , Assen 1989. Henry Teloh presents a detailed argument for a variant of the “revisionist” view: The Development of Plato's Metaphysics , University Park 1981, pp. 171-218. A moderate revisionist position takes William J. Prior: Unity and Development in Plato's Metaphysics , London 1985. In Prior's opinion, Plato did not consider the doctrine of ideas to be refuted, but had to respond to objections with modifications of his theory.
  75. Plato, Sophistes 246a – d, 248a ff.
  76. Theodor Ebert: Who are the friends of ideas in Plato's Sophistes? In: Rainer Enskat (ed.): Amicus Plato magis amica veritas , Berlin 1998, pp. 82-100 (advocates the Pythagorean hypothesis); Hermann Schmitz: The theory of ideas of Aristoteles , vol. 2: Platon and Aristoteles , Bonn 1985, pp. 5f., 42–53, 56–59, 146 (sees the idea friends as a group in the academy); Wilhelm Kamlah : Plato's Selbstkritik im Sophistes , Munich 1963, pp. 34–37; Michael Erler: Platon ( Outline of the history of philosophy. The philosophy of antiquity , edited by Hellmut Flashar, Volume 2/2), Basel 2007, p. 241f .; Wolfgang Wieland: Plato and the forms of knowledge , 2nd, extended edition, Göttingen 1999, pp. 107–112.
  77. See Robert Bolton: Plato's Distinction Between Being and Becoming . In: The Review of Metaphysics 29, 1975, pp. 66-95, here: 91-95; Hermann Schmitz: The theory of ideas of Aristoteles , Vol. 2: Platon and Aristoteles , Bonn 1985, pp. 72-79.
  78. Christoph Ziermann: Platon's negative dialectic , Würzburg 2004, pp. 55–58; Franz von Kutschera: Plato's “Parmenides” , New York 1995, pp. 40–44.
  79. Christoph Ziermann: Platon's negative dialectic , Würzburg 2004, pp. 40–66, 386–418; Franz von Kutschera: Plato's “Parmenides” , New York 1995, pp. 24–29, 37–40; introductory Michael Bordt: Platon , pp. 151–158.
  80. Aristoteles, Metaphysik 990b17, 1039a2–3.
  81. ^ Plato, Parmenides 132a-133a.
  82. A presentation of the entire train of thought in five steps is offered by Benedikt Strobel: Idea / Critique of Ideas / Third Person . In: Christoph Horn et al. (Ed.): Platon-Handbuch , Stuttgart 2009, pp. 289–296, here: 293.
  83. For the proposed solutions and their problems, see Béatrice Lienemann: The arguments of the third person in Plato's dialogue “Parmenides” , Göttingen 2010 and Benedikt Strobel: “This” and “So something”. On the ontological classification of Platonic forms , Göttingen 2007, pp. 18–31. See John Malcolm: Plato on the Self-Predication of Forms , Oxford 1991. For Malcolm, the problem of the third person arises from the failure to distinguish between two kinds of ideas: ideas as universals and ideas as patterns.
  84. On this proposal and its advantages and disadvantages see Béatrice Lienemann: The arguments of the third person in Plato's dialogue “Parmenides” , Göttingen 2010, pp. 139–185.
  85. See the presentation and discussion of this proposal in Béatrice Lienemann: The arguments of the third person in Plato's dialogue “Parmenides” , Göttingen 2010, pp. 287-316.
  86. ^ Béatrice Lienemann: The arguments of the third person in Plato's dialogue "Parmenides" , Göttingen 2010, pp. 353–387. See Franz von Kutschera: Platons Parmenides , 1995, pp. 29-35; Kutschera thinks that Plato rejected the assumption of non-identity.
  87. Knut Eming: The flight into thinking , Hamburg 1993, pp. 75-103.
  88. ^ Matthias Baltes: Idea (theory of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 225–227; Alice Swift Riginos: Platonica , Leiden 1976, pp. 147f .; Heinrich Dörrie , Matthias Baltes: Platonism in antiquity , Vol. 3, Stuttgart-Bad Cannstatt 1993, p. 292.
  89. See Harold Cherniss: The older academy , Heidelberg 1966, pp. 44–56; Leonardo Tarán: Speusippus of Athens , Leiden 1981, pp. 70-72; Hans Krämer: Speusipp . In: Hellmut Flashar (ed.): Outline of the history of philosophy. The philosophy of antiquity , Volume 3, 2nd edition, Basel 2004, pp. 13–31, here: 16f .; Hans Joachim Krämer: Aristotle and the academic doctrine of the Eidos . In: Archive for the History of Philosophy 55, 1973, pp. 119–190, here: 161–174.
  90. Detlef Thiel: The Philosophy of Xenokrates in the Context of the Old Academy , Munich 2006, pp. 351–356. However, a different opinion is John Dillon : The Heirs of Plato , Oxford 2003, pp. 118-120.
  91. Detlef Thiel: The Philosophy of Xenokrates in the Context of the Old Academy , Munich 2006, p. 370f .; Hans Joachim Krämer: Platonism and Hellenistic Philosophy , Berlin 1971, p. 343f.
  92. For Eudoxos' concept of ideas see Kurt von Fritz : Die Ideenlehre des Eudoxos von Knidos and their relationship to the Platonic doctrine of ideas . In: Kurt von Fritz: Writings on Greek Logic , Vol. 1, Stuttgart 1978, pp. 147–169; Hans Krämer: Eudoxos from Knidos . In: Hellmut Flashar (ed.): Outline of the history of philosophy. The philosophy of antiquity , vol. 3, 2nd edition, Basel 2004, pp. 56–66, here: 59–61; François Lasserre (ed.): The fragments of Eudoxus by Knidos , Berlin 1966, pp. 149–151; Russell M. Dancy: Two Studies in the Early Academy , Albany 1991, pp. 23-53; Hermann Schmitz: The theory of ideas of Aristoteles , Vol. 2: Platon and Aristoteles , Bonn 1985, pp. 157-161.
  93. ^ Gail Fine (ed.): On Ideas. Aristotle's Criticism of Plato's Theory of Forms , Oxford 1993 (critical edition of the fragments with English translation).
  94. See Renato Laurenti on this work: Les “dialogues” . In: Richard Goulet (ed.): Dictionnaire des philosophes antiques , Volume Supplément , Paris 2003, pp. 379–471, here: 395–409.
  95. See Hellmut Flashar: Die Platonkritik (I 4) . In: Otfried Höffe (Ed.): Aristoteles: Nikomachische Ethik , 2nd, edited edition, Berlin 2006, pp. 63–82.
  96. ^ Gail Fine: Forms as Causes: Plato and Aristotle . In: Andreas Graeser (Ed.): Mathematics and Metaphysics in Aristotle. Mathematics and metaphysics in Aristoteles , Bern 1987, pp. 69–112.
  97. Johannes Hübner: Aristotle on Separation and Causality , Hamburg 2000, pp. 92–94.
  98. See on this argument Knut Eming: The flight into thinking , Hamburg 1993, pp. 43–52.
  99. Chung-Hwan Chen: The Chorismos Problem in Aristoteles , Berlin 1940, p. 93f.
  100. Chung-Hwan Chen: The Chorismos problem in Aristoteles , Berlin 1940, p. 104f.
  101. Aristotle, On Becoming and Decaying 335b18-20.
  102. Aristotle, Metaphysics 987b7-14, 991a20-22, 1079b24-26. Cf. Francesco Fronterotta: ΜΕΘΕΧΙΣ , Pisa 2001, pp. 397-412; Rolf Schönberger : Participation . In: Historical Dictionary of Philosophy , Volume 10, Basel 1998, Sp. 961–969, here: 961; Matthias Baltes: Idea (theory of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 222f.
  103. See this argument Aristotle Thomas Alexander Szlezák: The incompleteness of academic principles theories of Aristotle's representation in Metaphysics M and N . In: Andreas Graeser (Ed.): Mathematics and Metaphysics in Aristotle. Mathematics and metaphysics in Aristoteles , Bern 1987, pp. 45–67, here: 49–64.
  104. See Hermann Schmitz: Die Ideenlehre des Aristoteles , Vol. 2: Platon and Aristoteles , Bonn 1985, p. 410.
  105. ^ Sources on this in Heinrich Dörrie, Matthias Baltes: Der Platonismus in der Antike , Vol. 4, Stuttgart-Bad Cannstatt 1996, pp. 118–123 (Commentary, pp. 387–399).
  106. ^ Matthias Baltes: Idea (theory of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 227f.
  107. Wolfgang L. Gombocz: The philosophy of the outgoing antiquity and the early Middle Ages , Munich 1997, p. 21f .; Roger Miller Jones: The Ideas as the Thoughts of God . In: Clemens Zintzen (Ed.): Der Mittelplatonismus , Darmstadt 1981, pp. 187–199; Audrey NM Rich: The Platonic Ideas as the Thoughts of God . In: Mnemosyne Series 4 Vol. 7, 1954, pp. 123-133; Hans Joachim Krämer: Der Ursprung der Geistmetaphysik , 2nd edition, Amsterdam 1967, pp. 21f., 111–116; Paul Oskar Kristeller : The ideas as thoughts of human and divine reason , Heidelberg 1989, pp. 13-17.
  108. Alkinous, Didaskalikos 9.1.
  109. Alkinous, Didaskalikos 9.2.
  110. Helmut Meinhardt: Idea. I. Antiquity . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 55–65, here: 61f.
  111. See Jens Halfwassen: Plotin and the Neo-Platonism , Munich 2004, pp. 74–77.
  112. ^ Matthias Baltes: Idea (theory of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 232.
  113. ^ Pieter d'Hoine: Four Problems Concerning the Theory of Ideas: Proclus, Syrianus and the Ancient Commentaries on the Parmenides . In: Gerd Van Riel, Caroline Macé (ed.): Platonic Ideas and Concept Formation in Ancient and Medieval Thought , Leuven 2004, pp. 9–29, here: 25.
  114. Syrianos, In Aristotelis metaphysica 147,2–6 Kroll; Greek text and German translation by Heinrich Dörrie, Matthias Baltes: Der Platonismus in der Antike , Vol. 5, Stuttgart-Bad Cannstatt 1998, p. 78f.
  115. ^ See on the argumentation of the Syrianos Alain de Libera: Der Universalienstreit , Munich 2005, pp. 89-98.
  116. ^ Rüdiger Arnzen: Platonic Ideas in Arabic Philosophy , Berlin 2011, p. 8f.
  117. ^ Matthias Baltes: Idea (theory of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 238f.
  118. ^ Matthias Baltes: Idea (theory of ideas) . In: Reallexikon für Antike und Christianentum , Volume 17, Stuttgart 1996, Sp. 213–246, here: 239–241, 243–245.
  119. ^ Augustine, De diversis quaestionibus 46.
  120. Helmut Meinhardt: Idea. I. Antiquity . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 55–65, here: 63f.
  121. ^ Augustine, De diversis quaestionibus 46.
  122. Helmut Meinhardt: Idea. I. Antiquity . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 55–65, here: 64.
  123. ↑ On these questions and their mediaeval reception, see Alain de Libera: Der Universalienstreit , Munich 2005, pp. 40–47.
  124. Gangolf Schrimpf et al.: Idea. II. Middle Ages . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 65-102, here: 68-72.
  125. See on Bernhard's concept Theo Kobusch: The Philosophy of the High and Late Middle Ages , Munich 2011, pp. 99-101.
  126. Gangolf Schrimpf et al.: Idea. II. Middle Ages . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 65-102, here: 77-79.
  127. ^ Roland J. Teske: Studies in the Philosophy of William of Auvergne, Bishop of Paris (1228–1249) , Milwaukee 2006, pp. 161–178.
  128. ^ Latin ideae separatae , also formae separatae or species separatae per se subsistentes .
  129. Thomas von Aquin, Summa theologiae I quaestio 6 articulus 4. On Thomas' criticism of the doctrine of ideas, see Gregory T. Doolan: Aquinas on the Divine Ideas as Exemplar Causes , Washington (DC) 2008, pp. 192–195, 228–232 .
  130. ^ Ockham's position is described by Jan P. Beckmann : Wilhelm von Ockham , Munich 1995, pp. 98-134. Beckmann offers a brief summary in the Idea article . II. Middle Ages . In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 65-102, here: 99-101.
  131. Rüdiger Arnzen: Platonic Ideas in Arabic Philosophy , Berlin 2011, pp. 8–11, p. 67 and note 217.
  132. Rüdiger Arnzen: Platonic Ideas in the Arab Philosophy , Berlin 2011, pp. 3–5, 12–66, 75–99.
  133. Immanuel Kant, Critique of Pure Reason B8 f. For Kant's criticism of the theory of ideas, see Walter Patt: Forms of Anti-Platonism in Kant, Nietzsche and Heidegger , Frankfurt am Main 1997, pp. 7–22.
  134. Karl Neumann gives an overview of modern idea concepts and their relationship to older ideas: Idea. IV. In: Historical Dictionary of Philosophy , Volume 4, Basel 1976, Sp. 113-134, here: 119-133.
  135. On the modern rejection and criticism of an ontological theory of ideas see Klaus-Dieter Eichler : Idea . In: Petra Kolmer, Armin G. Wildfeuer (eds.): New Handbook of Philosophical Basic Concepts, Vol. 2, Freiburg 2011, pp. 1186–1199, here: 1186f. and Terry Penner: The Ascent from Nominalism , Dordrecht 1987, pp. 1-11.
  136. Georg Wilhelm Friedrich Hegel: Lectures on Aesthetics , Vol. 1 (= Complete Works. Anniversary Edition in Twenty Volumes , Vol. 12), Stuttgart 1953, p. 46.
  137. ^ Friedrich Nietzsche: Götzen-Twilight . In: Friedrich Nietzsche: Works in three volumes , ed. by Karl Schlechta , Vol. 2, Munich 1966, pp. 939-1033, here: 963.
  138. ^ See on Heidegger's criticism of Walter Patt's theory of ideas: Forms of Anti-Platonism in Kant, Nietzsche and Heidegger , Frankfurt am Main 1997, pp. 220–222, 241–253.
  139. ^ Dorothea Frede: Plato. In: Otfried Höffe (Ed.): Klassiker der Philosophie , Vol. 1, Munich 2008, pp. 26–49, here: 32 f., 41.
  140. See the overview in Necip Fikri Alican: Rethinking Plato , Amsterdam / New York 2012, pp. 110–129.
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