Jean Piaget

from Wikipedia, the free encyclopedia
Piaget (1972)
Bust of Jean Piaget in the Parc des Bastions in Geneva

Jean Piaget [ ʒɑ̃ pjaˈʒɛ ] (born August 9, 1896 in Neuchâtel , † September 16, 1980 in Geneva ) was a Swiss biologist and pioneer of cognitive developmental psychology as well as the founder of genetic epistemology . The latter was one of the great research programs developed in the 20th century for the scientification of epistemology , traditionally regarded as part of philosophy, or, in the French context, epistemology . "Genetic" is to be understood in the sense of "relating to the genesis (history of origin, development)" (and thus mostly not in the sense of "hereditary programmed" or "relating to hereditary information").


Unmarked grave of Jean and Valentine Piaget, Cimetière des Rois , Geneva

As a child, Piaget published numerous biological essays, which made him "an internationally respected expert in a few years". The basis for this was above all his long-term assistance to the director of the local museum for natural history, which he started at the age of ten (1907), as well as his specialization in molluscology ( malacology ), which he undertook against this background . He completed his biology studies at the University of Neuchâtel at the age of 22 (some sources also say 1917, i.e. with a maximum of 21 years) with a doctorate.

From around his sixteenth birthday, Piaget, who was rooted in the Protestantism of his homeland in western Switzerland until his early adult years, also dealt intensively with philosophy - which, however, led him less to a reorientation than to the fact that he no longer focused solely on the biological problem interested in the adaptation of the organism to its environment, but saw "in biology the explanation of all things and the spirit itself" and finally made the decision to dedicate his life "to the biological explanation of knowledge".

In 1921 he was appointed to the University of Geneva , to the Jean-Jacques Rousseau Institute , of which he was director from 1933 to 1971. In 1923 he married Valentine Châtenay. His three children were among other things subjects of study for his groundbreaking research on the development of intelligence from birth to the acquisition of a first language . From 1929 to 1954 he was professor of psychology at the University of Geneva and then head of the Center International d'Épistémologie Génétique , also in Geneva, founded in 1955 . He also held professorships at the University of Neuchâtel and at the Sorbonne in Paris.

Work and theory

Jean Piaget's work is primarily an epistemological and psychological work, but it is based on the idea of ​​explaining knowledge biologically, more precisely on the basis of a biology that starts from the concept of the "biological system". This approach had been replaced in biology from the 1950s by orthodox molecular genetics , but from around 2000 it was recognized that the activity of genes in turn is regulated by the situation of the entire organism (the entire "biological system").

The central idea of epistémology ( philosophy of science or epistemology ) of Piaget is that human intelligence and knowledge, based on the way the organism deals with its environment, must be understood in terms of processes. This includes simple learning in the sense of the classical behaviorism dominating at the beginning of the 20th century - conditioning and habituation - as a borderline case, but goes beyond why Piaget uses the stimulus-response scheme, which is at the center of classical behaviorism, around the organism as the third, mediating element added.

The theoretical armament of Jean Piaget also includes Immanuel Kant , whose epistemological theory he did not want to refute but on the contrary to substantiate, the pragmatism of John Dewey , which also followed Kant, and the French psychology of the early 20th century ( Édouard Claparède et al.), Not so much gestalt psychology . In addition, Piaget enthusiastically took up modern, structuralist mathematics ( Nicolas Bourbaki ) and cybernetics , which from the 1940s also made use of formal models of the mind.

Cognitive functions

At the center of Piaget's theory are two complementary functional processes that already characterize the purely biological field: assimilation on the one hand and accommodation on the other. Both are aspects of the adaptation (adaptation) of the individual to his environment, because in the exchange relationship between man and environment two types of adaptation are possible: on the one hand, adapting one's own behavior to the outside world (example: the child imitates the parents), others adapt the outside world to their own behavior (for example in the symbolic children's game: "I would be the mother now and you would be the baby now ...").

The analogy of food intake, used by Piaget himself, serves to illustrate this further: the ingestion of food, its chewing and the material decomposition means assimilation in the sense of adaptation to the organism. However, the organism itself also adapts to the food, as it has to take into account the particularities of the food in question when it is ingested (for example, soup is not chewed).

An example cited at times is the child's act of grasping in the early stages: the child is born with a grasping reflex . An object that is initially touched by chance and then automatically grasped is assimilated to the act of grasping, so to speak. The object is something that the child can grasp. For the child at this point in time it only exists as such, so to speak as a "gripping object" and not yet as an object in the usual sense with all its sensory properties (see object permanence ).

The assimilation movement is now repeatedly practiced on this object. The object forms "food" for the gripping scheme. The child naturally encounters other objects. These are also assimilated to the schema. However, the same gripping action can no longer be carried out. A toy car has to be grasped differently than a rattle . The example becomes even more concise when a toddler tries to grab water. The developed gripping pattern must be adapted to the new object, i.e. accommodated, in the case of water a scooping movement results. Piaget calls the incorporation of the gripping scheme of a number of objects generalizing assimilation.

Explicitly, assimilation means something like cognitive integration of sensory perceptions and accommodation of the differentiation of these (already integrated) sensory perceptions. These two processes form the basis for the differentiation of a model of the environment and are the basis for the worldview of the child (and also of the adult).

Theory of the Origin of Identity

Piaget sees people as an open system. By this he understands an organism that changes, reacts to environmental influences, adapts and influences the environment itself. Thus man divides his world. The system remains open.

A lot is possible in this open system. Nevertheless, there are limits to humans, e.g. B. the biological limit. The openness of the system includes thought structures and feelings that other people cannot easily recognize.

Piaget is of the opinion that people strive for a constant balance, that they try to achieve their balance ( equilibration ). This is done through assimilation or accommodation (see above). If this fails, an imbalance occurs (de-equilibrium). But the organism strives for knowledge or has a need for knowledge of what is meaningful for it. Being becomes active through its drive, the open system develops.

According to Piaget, identity is created through the constant striving for balance and the dissolution of imbalance.

Cognitive development

The stages of cognitive development are classified according to Piaget's development model as follows: (see also Klann-Delius (1999))

  1. Stage of sensorimotor intelligence (0–2 years): acquisition of sensorimotor coordination, practical intelligence and object permanence ; Object permanence but still without internal representation
  2. Stage of preoperational intelligence (2-7 years): acquisition of the ability to imagine and speak; characterized by realism , animism and artificialism (in summary: egocentrism ); can now distinguish between animate and inanimate
  3. Stage of concrete operational intelligence (7-11 years): Acquiring the ability to think logically in relation to concrete (actual or imagined, but not hypothetical) facts. This is associated with decentering , reversibility , invariance, seriation, class inclusion and transitivity
  4. Stage of formal operational intelligence (from 11 years): Acquisition of the ability to hypothetical logical thinking , which means the ability to apply the concrete logical operations of level 3 to other such operations

These four stages have the following characteristics:

  • the individual stages follow one another; one stage must be passed before the next can follow
  • the stages occur in all cultures
  • In different task areas, the stage development takes place at different speeds (décalage horizontal), because the completely abstract mastery of the cognitive structures is only achieved at level 4 and the skills remain tied to certain content beforehand
  • the stages are delimited from one another by qualitative , not just quantitative, differences, which can, however, be reconstructed in terms of the behavior of a complex dynamic system (ultimately as a result of the increase in the degree of coordination)
  • In the stages, through the processes of assimilation and accommodation, a better adaptation of the person to the conditions caused by the environment (adaptation) is sought. Accommodation in particular happens when an imbalance between the already established cognitive structures and real situations is discovered through new experiences. These two processes are stimulated by maturation , by experience and by education and this leads to the going through of the individual cognitive stages.

Stage of sensorimotor intelligence

  • 0–1 month (innate reflex mechanisms): At birth, the child is locked in a state of absolute egocentrism ; it perceives nothing but itself. The child's movements are simple spontaneous movements and reflexes such as sucking, following moving objects with the eyes, closing the hand when touched, involuntary kicking, etc .; these reflexes later become voluntary actions.
  • 1–4 months (primary circular reactions ): New reaction patterns are formed by a random combination of primitive reflexes. The child combines separate actions, e.g. B. fidget with your hand and suck on it.
  • 4–8 months ( secondary circular reactions ): The child reacts to external stimuli, but seeing and grasping are not yet coordinated. First attempts are made to act on the environment, e.g. B. by generating the sound of a rattle.
  • 8–12 months ( intentional behavior ): Targeted behavior emerges. An obstacle is pushed aside to grab an object. Object permanence now arises . At this age, the eight-month fear (“strangling”) also appears: the child can now distinguish which people are familiar and which people are foreign to him. While it used to smile at all human faces, it now only smiles at people who are familiar to it. It reacts repulsively to faces that are alien to it.
  • 12–18 months ( tertiary circular reactions): Directed touch, tools are needed, trial-and-error behavior is aimed at a goal.
  • 18–24 months ( transition to the pre-operational phase): The child begins to develop spiritually. Movements and their effects can increasingly be represented symbolically, i.e. considered in the imagination. It gives up its egocentric point of view on the physical, not yet on the spiritual, level.

Stage of preoperational intelligence

The child is increasingly replacing sensorimotor activities with internalized mental activities such as linguistic expression and visualization. It acts in thought. A child who cannot escape the compelling aspects of the immediate concrete stimulus and cannot imagine what the object looked like before a change is in the preoperational, pre-thought stage.

In the preoperational stage, the child still sees himself as the center with his needs and purposes. Everything is seen in relation to the self . The egocentrism of the preoperational child leads them to assume that everyone thinks as they think for themselves and that the whole world shares their emotions, feelings and desires. Due to their childlike egocentrism, the child is not able to put themselves in other people's shoes and assumes that everyone around them shares their perspective. Due to their lack of understanding of causality, the child believes that everything that it considers real (images or dreams) exists and is animated as it is. This is called animism. It is also self-centered on the linguistic level. The child is unable to tell a story in a way that is understandable to a listener who does not know the story. In conversations, too, there is little focus on dialogue partners and monologues or collective monologues (cf. Klann-Delius 1999: 111). Piaget's concept of egocentric speaking influenced the Russian developmental and language psychologist Lev Vygotsky , who at the end of the 1920s and early 1930s examined the concept in depth and critically and developed his own alternative.

Piaget distinguishes four stages in relation to animism, which are passed through one after the other:

  1. Any object can be charged with a purpose or conscious activity. A ball may refuse to go straight
  2. Only objects that move are alive (e.g. clouds)
  3. Only objects that move spontaneously and on their own are alive
  4. Only plants and animals are alive

Under artificialism refers to the notion that the objects and natural phenomena were created by humans. For example, humans could create stars, mountains, and rivers. The preoperational child's thinking is not based on logic . Objects and processes that occur in a spatiotemporal context are seen in a causal relationship, for example thunder makes rain.

Stage of concrete operational intelligence

The child can operate logically in their thoughts with concrete objects or their ideas. Thought is therefore already logical, but only if it is supported by concrete intuition.

  • Decentering is the process following immediate and ego-centered perception. The decentering corrects errors or distortions in perception. It is no longer the superficial, most conspicuous aspect of perception that is rated the most
  • Reversibility (reversibility) is the ability to perform mental operations in reverse order; d. i.e., operations that have been carried out can be reversed (addition - subtraction)
  • Under invariance (immutability) is to understand the knowledge that certain properties of an object are constant and are retained, even if it changes its appearance. Examples: preservation of the substance even if the shape changes; Preservation of weight when changing shape; Preservation of volume, even if the water is filled into a higher vessel; Maintaining the length of a stick even when it is moved; Preservation of the number, even if the arrangement ( instead of ) is changed
  • Seriation is the ability to arrange objects in an order based on size, appearance, or some other characteristic
  • Classification means the ability to name or identify a group of objects according to their appearance, size or some other characteristic. This includes the idea that one class can contain another class (see mathematical : inclusion mapping )

Stage of formal operational intelligence

Young people can now “operate with operations”, that is, they can think not only about concrete things, but also about thoughts, think abstractly and draw logical conclusions from mere hypotheses.

Paradigmatic experiments

Piaget conducted many behavioral experiments / tests for his research, some with his own children. Here are some of his most famous and important experiments:

  • An object is hidden from the child's eyes by a screen. The child looks surprised and acts as if the object has vanished into thin air. According to Piaget, a child who behaves in this way has not yet developed object permanence .
  • A glass container A is filled with water, glass container B is empty. The water is completely poured from container A into B. Since B is narrower and more elongated than A, the water in B is now higher than it was in A. A child who has not yet learned the invariance of volumes answers that there is now more water in B than before in A.
  • Two balls of the same size made of modeling clay are shaped into a sausage in front of the child. The child claims the plasticine has changed. Although it recognizes the identity of the deformed sphere, it states that the mass has increased (“becomes longer”) or decreased (“has become thinner”). According to Piaget, the problem is solved incorrectly because the child does not have reversibility skills and is limited to only one dimension of transformation (centering).
  • Two toy cars A and B drive and stop at the same time. A drives faster than B. The child thinks A drove longer than B. Explanation: Confusion of the parameters time (t) and distance (s).
  • An equal number of pieces are arranged in a row. The spacing of one row is shorter than that of the second. Result: The first row consists of fewer pieces for the child. Even if you let the child count both rows, it sticks to its judgment. Ginsburg (see literature: Entering the Child's Mind ) expanded this attempt: He added another gaming chip to the shorter row. Even this didn't change the child's answer.
  • Three-mountain experiment: The child is shown a landscape with three mountains of different heights. The child is in position 1 and is asked to choose their own perspective from a series of given images, which they can do. Now the child is led to position 2 and in turn recognizes their own perspective in the pictures. After the child is brought back to position 1 and is asked what the landscape of position 2 looks like, it chooses its own perspective from position 1. According to Piaget, this indicates a lack of perspective or childish egocentrism.


Appreciation and influence


There are basically three types of criticism of Piaget's theory. On the one hand, this is directed against Piaget's method and, on the other hand, against his division of cognitive development into different stages and stages. Many experiments have been carried out to show that children have skills in stage X which, according to Piaget, they should only have in stage Y. Another more fundamental criticism turns against the circular procedure, by means of the assumption of fundamental genetic principles, which Piaget assumes as the abstract totality of the cosmos, to use all of his research examples, which are quite interesting for themselves, as evidence for his (epistemological) development principle:

Piaget presents his work as a reciprocal justification between his experiments and his development model. He assumes that the results of individual developmental steps are necessary because they follow a genetic developmental principle. The abstract and functional adaptation is defined as the reason for all the individual learning steps that children take - i.e. not derived from the experiments. If Piaget were to explain or predict a certain result of childlike thinking by means of the concept of adaptation, he would constantly come across various possibilities, the differences of which could just be explained. Under the abstract concept of equilibrium - beyond certain content - he can classify every result of learning because he has eliminated every possible contradiction by definition and in advance in the abstractness of his equilibrium principle . Balance is then always exactly the state that was already known as the result of each specific learning step. The theoretical terminology gives the development a name in order to formally express the necessity of the learning step. You're not explaining it by that. In this way, Piaget makes himself independent in his theory of the substantive results of his investigations. From the result, he transfers his observations to his abstractions. All observations fit together without the abstract categories, which Piaget named and explained as the reason for development, having to be in a derivation context to experiments or observations. As an interpretation model, the theory makes the postulated necessity of any development steps plausible.

Methodically, Piaget took a different position throughout his life than the established behaviorist (positivist) psychology. He considered the use of parametric statistics and standardized research methods to be counterproductive. In his early work, he adapted the clinical interview method commonly used in psychiatry . It was soon discovered that the statements in the “child's worldview” contained artifacts of the suggestive effects of the interview questions and techniques. The method was revised and from then on Piaget founded the “revised clinical method” (Ginsburg & Opper, 2004) or also called the critical exploration method (Inhelder, Sinclair & Bovet, 1974, p. 35: méthode d'exploration critique ; Ducret, 2004) the definition of the critical method as follows:

“Nous avons donc totalement renoncé à la méthode de pure et simple conversation, à la suite de nos recherches sur les deux premières années du développement, pour adopter une méthode mixte dont nous avons pu éprouver, depuis lors, la fécondité bien supérieure. Cette “méthode critique” (s'il est permis de baptiser ainsi l'aboutissement des procédés que nous avions primitivement empruntes à la “méthode clinique” des psychiatres) consiste toujours à converser librement avec le sujet, au lieu de se borner à des questions fixes et standardisées, et elle conserve ainsi tous les avantages d'un entretien adapte à chaque enfant et destiné à lui permettre le maximum possible de prize de conscience et de formulation de ses propres attitudes mentales; mais elle s'astreint à n'introduire questions et discussions qu'à la suite, ou au cours même, de manipulations portant sur des objets suscitant une action déterminée de la part du sujet. (Piaget, 1967, p. 7) "

Piaget carried out first investigations with the revised method mainly on his three children. The results led to the draft of the step theory on sensorimotor, preoperational and concrete thinking operations (Ginsburg & Opper, 2004). Studies of formal operations followed later (Ginsburg & Opper, 2004; Inhelder & Piaget, 1980). Piaget's qualitative methods have often been described as unscientific. However, it is disputed whether such a designation does not fall short in view of the subtlety of Piaget's methodology. Piaget about his own approach:

“A good experimenter has to combine two often incompatible characteristics: he has to observe, be able to let the child speak, he must not slow down the flow of speech, not lead it in the wrong direction, and at the same time he has to have a sensorium to get something precise out of it . He must always have a working hypothesis, a theory, whether right or wrong, at hand ... Beginners suggest what they want to find to the child, or they suggest nothing at all because they are not looking for anything and then they will not find anything. "

- Piaget : The child's worldview


“The trouble with Piaget and his stages is that every time he gives an example of it, you feel like the hero in Jerome K. Jerome (in Three Men in a Boat ), who is reading a medical dictionary discovered the symptoms of all diseases. One has the impression that one is in the middle of it all, in each of these Piagetian stages. As far as I'm concerned, I feel completely preoperative, because the relationships between cause and effect seem very weak here. "

- Stella Baruk : How old is the captain? About the mistake in mathematics. (French original edition: Edition Du Seuil, Paris 1985), German translation Birkhäuser, Basel 1989, p. 232

Piaget's works

collected works at Klett-Cotta
  1. The awakening of intelligence in the child
  2. The structure of reality in the child
  3. The development of the number concept in children (with Alina Szeminska)
  4. The development of physical quantity concepts in children (with Bärbel Inhelder)
  5. Imitation, play and dream
  6. The development of spatial thinking in children (with Bärbel Inhelder)
  7. The natural geometry of the child (with Bärbel Inhelder and Alina Szeminska)
  8. The development of knowledge. Volume I: Mathematical Thinking
  9. The development of knowledge. Volume II: The physical thinking
  10. The development of knowledge. Volume III: Biological Thinking. Psychological thinking. Sociological thinking

Key texts in 6 volumes published by Klett-Cotta and revised by Richard Kohler (2015)
  1. The child's worldview
  2. Theology and Reform Education
  3. The child's moral judgment
  4. Psychology of intelligence
  5. Structuralism
  6. Genetic Epistemology

See also



Selected introductions
  • J. Flavell: The developmental psychology of Jean Piaget. Van Nostrand, New York 1963.
  • H. Ginsburg, S. Opper: Piaget's theory of intellectual development. An introduction. Prentice-Hall, New Jersey 1969.
    • German translation: Piaget's theory of intellectual development (9th edition). Klett-Cotta Verlag, Stuttgart 2004, ISBN 3-608-91909-0 .
  • Herbert P. Ginsburg: Entering the Child's Mind. The Clinical Interview in Psychological Research and Practice. Cambridge University Press, 1997, ISBN 0-521-49803-1 .
  • Thomas Kesselring: Development and Contradiction. A comparison between Piaget's genetic epistemology and Hegel's dialectic. Suhrkamp, ​​Frankfurt am Main 1981.
  • Thomas Kesselring: Jean Piaget. Verlag CH Beck, Munich 1999, ISBN 3-406-44512-8 .
  • Richard Kohler: Jean Piaget. UTB, Stuttgart, 2008.
  • Richard Kohler: Piaget and Pedagogy: A Historiographical Analysis. Klinkhardt, Bad Heilbrunn 2009.
  • L. Montada: The spiritual development from the point of view of Jean Piaget. In: R. Oerter, Montada (Ed.): Developmental Psychology. Beltz-Verlag, Psychologie-Verlags-Union, Weinheim 1987.
  • Herbert P. Ginsburg, Susan F. Jacobs, Luz Stella Lopez: The Teacher's Guide to Flexible Interviewing in the Classroom. Learning what Children know about Math. Allyn & Bacon, Needham Heights 1998, ISBN 0-205-26567-7 .
  • U. Müller, JIM Carpendale, L. Smith (Eds.): The Cambridge Companion to Piaget. Cambridge University Press, Cambridge, 2009, ISBN 0-521-89858-7 .
  • K. Reusser: Jean Piaget's theory of the development of knowledge. In W. Schneider, F. Wilkening (Ed.): Encyclopedia of Psychology. Developmental Psychology Series . Volume I: Theories, Models and Methods in Developmental Psychology. Hogrefe, Göttingen 2006, pp. 91-189.
  • Ingrid Scharlau: Jean Piaget for an introduction. 2. completely revised Edition. Junius, Hamburg 2007, ISBN 978-3-88506-646-0 .
  • Smith, L .: Jean Piaget. In: JA Palmer Cooper (Ed.): The Routledge Encyclopedia of Educational Thinkers . Routledge, Abingdon 2016, ISBN 978-1-138-82614-4 , pp. 319-324.

Web links

Individual evidence

  1. ^ Thomas Kesselring: Jean Piaget. CH Beck, Munich 1988, p. 18.
  2. ^ Thomas Kesselring: Jean Piaget. CH Beck, Munich 1988, p. 18f.
  3. ^ A Jean Piaget en l'honneur de son 80ème anniversaire. 1976 Center de télévision, p. 25.
  4. ^ A b Jean Piaget: Autobiography. In: Jean Piaget, work and effect. Munich 1976, pp. 15–59, here: 20.
  5. ^ Jean Piaget: Autobiography. In: Jean Piaget, work and effect. Munich 1976, pp. 15–59, here: pp. 19–20.
  6. Ludwig von Bertalanffy: General System Theory. Foundations, Development, Applications. New York 1968.
  7. Thomas Kesselring: Development and Contradiction. A comparison between Piaget's genetic epistemology and Hegel's dialectic. Suhrkamp, ​​Frankfurt / Main 1981; P. 40 ff.
  8. ^ Jean Piaget: Biology and Knowledge. About the relationships between organic regulations and cognitive processes. Frankfurt am Main 1992 (1967), pp. 8-11.
  9. John Dewey: The Search for Certainty. An investigation into the relationship between knowledge and action. Frankfurt am Main 2001 (1929).
  10. Jean Piaget: Les modèles abstraits sont-ils opposés aux interprétations psycho-physiologiques dans l'explication en psychologie? In: Bulletin de psychologie, 13, No. 169, pp. 7-13
  11. ^ J. Piaget: The world view of the child. dtv / Klett-Cotta, Munich 1978.
  12. Jean Piaget: My theory of mental development . Ed .: Reinhard Fatke. tape 142 . Beltz, 2003, ISBN 3-407-22142-8 , pp. 156 .
  13. Vygotskij, Lev S. (1934/2002). Thinking and speaking . Edited and translated from Russian by Joachim Lompscher and Georg Rückriem. Weinheim and Basel: Beltz.
  14. ^ King's College London - Cognitive Acceleration (CASE and other projects) . 2012 [last update]. Retrieved March 16, 2012.
  15. P. Adey, M. Shayer: Really Raising Standards. Routledge, London 1994.
  16. M. Shayer, PS Adey (ed.): Learning Intelligence: Cognitive Acceleration across the curriculum from 5 to 15 years. Open University Press, Milton Keynes 2002.
  17. Friedrich H. Steeg: Learning and selection in the school system using the example of “arithmetic weaknesses”: Multi-level analysis of the functions of our education system and an attempt at an ideology-critical conclusion on didactic approaches and practical implementation. Publication series educational psychology, 5th Lang, Frankfurt am Main et al. 1996, ISBN 3-631-30731-4 ; Pp. 41-57.
  18. JWP Allen MH Bickhard: Stepping off the pendulum: Why only an action-based approach can transcend the nativist-empirical debate. In: Cognitive Development, 28 (2), 2013, pp. 96-133.
  19. ^ B Inhelder, H. Sinclair, M. Bovet: Apprentissage et structures de la connaissance. Presses Universitaires de France, Paris 1974.
  20. J.-J. Ducret: Méthode clinique-critique piagetienne. 2004, p. 19: Service de la recherche en éducation du canton de Genève
  21. ^ Piaget, J. (1967). Le jugement et le raisonnement chez l'enfant (6ème édition). Neuchâtel: Delachaux et Niestlé.
  22. B. Inhelder, J. Piaget: From the logic of the child to the logic of the adolescent. Walter-Verlag, Olten 1980.
  23. R. Diriwächter, J. Valsiner: Qualitative methods in developmental psychology: historical and epistemological context. [Internet]. 2006. online [26. March 2012]