Influxus physicus

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As influx physicus (. Lat INFLUERE - flow, penetrate, influence and gr. Physis - nature ;. French influence naturelle , influence physique , influence real ) was called in the 17th century the influence of the different between two substance areas is causally effective. The assumption that there is such a physical influence is a central thesis of the philosophical mind-body problem . Theories that support this thesis are called influxionism ( systema influxus physici ) or psychophysical interactionism .

Concept history

Origin of the term

The origin of the term lies in the high scholasticism . Thomas Aquinas , for example, speaks of an influence of the actively understood soul on the passively understood body : “What is in activity ( actus ) has an effect on what is in potentiality ( potentia ); and such a movement is said to have an influence ( influxus ). ”He has not yet discussed the opposite influence, that is, an effect of the body on the soul. The later specification with the addition " physicus " expresses that the influence is to be understood as causal . In this respect, the understanding of the late scholasticist Francisco Suárez was particularly influential : " Influxus physicus is what happens through a real and real causality ( veram causalitatem realem ) [...]." However, since scholasticism does not yet make a substantial difference between soul and assumed body, the influxus physicus was not yet a debatable term for them. Soul and body were understood as a unit ( unio substantialis ), which was unproblematic with regard to the influence of the soul on the body.


Influxus physicus became a debatable term in the 17th century. The assumption that there is a physical influence becomes a central problem in the early philosophy of mind at the beginning of René Descartes . According to a classic presentation, the problem arises from three incompatible assumptions:

1. Substance dualism: Reality consists of two substances, a thinking substance ( substantia cogitans ) and an extended substance ( substantia extensionis ).
2. Influxionism: There is an influxus physicus - now explicitly understood as a causal interaction ( influence mutelle ) between the two substance areas of the extended and the thinking.
3. Causal closure: the area of ​​extended substance is causally closed.

The third assumption is closely related to Descartes' law of conservation of energy , according to which the amount of energy (or amount of movement) does not increase in the extended substance area. It was created once by God with the world and has remained the same size ever since. This assumption, however, contradicts the second, according to which an increase takes place qua influxus physicus .

Descartes' own position on this inconsistency ultimately remained indifferent because he did not discuss the problem directly. According to Rainer Specht , Descartes himself should therefore not yet be considered a representative of influxionism or psychophysical interactionism . The theory of influxionism, usually attributed to Descartes, only applies historically to authors such as Andreas Rüdiger , who resolutely defended influxionism in response to the criticism of Descartes. Nonetheless, Descartes implicitly made the following suggestion to resolve the inconsistency of the three assumptions: Although the soul cannot impart any new movement to the body, it can change the direction of its movement. The change in direction of the movement is already sufficient to speak of a free will decision of the soul, which can only be spoken of if the soul influences the body in some way.


Descartes' approach has two famous mistakes: As Gottfried Wilhelm Leibniz has shown, on the one hand he disregards the conceptual difference between movement and force and on the other hand the Galilean law of inertia , according to which no movement changes direction without an impulse . Descartes therefore fails to remove the inconsistency of the second and third assumptions. Approaches to a solution that denied the influxus physicus due to this inconsistency , but remained committed to Cartesian substance dualism , later became known as the teachings of so-called occasionalism . The main thesis of occassionalism is that the influxus physicus only appears as such. Indeed, God mediates between body and mind through occasional causes.

Occasionalism, on the other hand, was criticized by Leibniz on the one hand for the fact that the mediation of God opposed his perfect creation of the world. He sees a second problem in the fact that the occassionalists clung to the substance dualism , which makes the assumption of an influxus physicus necessary in the first place. Leibniz therefore advocates abandoning not only the second (influxionism) but also the first assumption (substance dualism) of the mind-body problem. With the system of pre-established harmony postulated by him , he proposes to understand the areas of the psychic and the physical as different perspectives, which completely coincide due to a perfect parallelism established by God .

In the current discussion of the philosophy of mind, the influxus physicus is still frequently referred to as a historical starting point. Substantive dualistic influxionism as a solution to the mind-body problem is, however, an outdated position and today has practically no representatives.


  • Peter Bieri : General introduction . In: Peter Bieri (Ed.), Analytical Philosophy of Mind. 2nd Edition. Athenäum-Hain-Hanstein-Verlags-Gesellschaft, Bodenheim 1993, ISBN 978-3-8257-3006-2 , pp. 1-28.
  • Michael Pauen : Basic Problems of the Philosophy of Mind. An introduction. Fischer Verlag, Frankfurt a. M. 2005, ISBN 3-596-14568-6 , pp. 34-48.
  • Rainer Specht : Commercium mentis et corporis. About causal ideas in Cartesianism. Friedrich Frommann Verlag (Günther Holzboog), Stuttgart-Bad Cannstatt 1966.

Web links

Individual evidence

  1. ^ Thomas Aquinas : Questiones de quolibet . Quodlibet III., 3a, 2co .
  2. ^ Francisco Suárez : Disputationes metaphysicae . Disp. XVII, sec. II, § 6 .
  3. See Peter Bieri : General Introduction . In: Peter Bieri (Ed.): Analytical Philosophy of Mind. 2nd Edition. Athenäum-Hain-Hanstein-Verlags-Gesellschaft, Bodenheim 1993, ISBN 978-3-8257-3006-2 , p. 5.
  4. See René Descartes : Les Passions de l'âme . Henry Le Gras, Paris 1649, I, § 34. Quoted from Christian Wohlers (Ed.): The Passions of the Soul , Felix Meiner Verlag, Hamburg 2014, ISBN 9783787326853 , pp. 23–24.
  5. See René Descartes: Principia philosophiae . Louis Elsevier , Amsterdam 1644 ( at Google Books ), II, § 36. Quoted from Christian Wohlers (ed.): The principles of philosophy . Felix Meiner Verlag, Hamburg 2007, ISBN 978-3-7873-1853-7 , pp. 136-139.
  6. Cf. Rainer Specht : Influxus physicus, Influxionismus . In: Joachim Ritter , Karlfried founder , Gottfried Gabriel (Hrsg.): Historical dictionary of philosophy . Vol. IV, Basel 1984, pp. 355-356.
  7. Cf. Michael Pauen: Basic Problems of the Philosophy of Spirit. An introduction . Fischer Verlag, Frankfurt a. M. 2005, ISBN 3-596-14568-6 , pp. 41-46.
  8. See Gottfried Wilhelm Leibniz : Brevis demonstratio erroris memorabilis Cartesii etc. In: Acta Eruditorum . Vol. V, Leipzig 1686, pp. 161-163.
  9. Cf. Immanuel Kant : Critique of Judgment . Lagarde and Friederich, Berlin and Libau, § 81. Quoted from Kant's Gesammelte Schriften (Academy edition). Vol. 5, published by the Royal Prussian Academy of Sciences in Berlin , Dietrich Reimer Verlag , Berlin 1913, p. 422.
  10. Cf. Rainer Specht: Occasionalismus . In: Joachim Ritter , Karlfried founder , Gottfried Gabriel (Hrsg.): Historical dictionary of philosophy . Vol. VI, Basel 1984, pp. 1090-1091.
  11. See Hubertus Busche : windowlessness. Leibniz 'critique of the Cartesian' Influxus Physicus' and his idea of ​​energetic self-causality. In: Albert Heinekamp, ​​Ingrid Marchlewitz (ed.): Leibniz 'analysis of predecessors and contemporaries . Stuttgart 1990, pp. 100-115.
  12. Cf. Raphael Borchers: On the substance-dualistic misunderstanding of Leibniz's hypothèse des accords. In: Philosophical Yearbook . Vol. 123, Verlag Karl Alber, Freiburg / Munich 2016, pp. 38–57.
  13. Cf. Albert Newen : Philosophy of Spirit. An introduction. CH Beck, Munich 2013, pp. 17-21.