MOTION. — M. in general, or change, is the passage from one mode of being to another: in this sense everything moves, except God, pure act.
The Eleatic school denied every m. (v. ELEATIEMO). Zeno, supposing local m. to be composed of infinitely many parts, demonstrated its absurdity by means of the four apories: dichotomy, Achilles, the arrow, and the stadium (cf. Aristotle, Phys., VI, 9). Leucippus and Democritus affirmed the local m. of atoms in the void; it is the only possible m. (id., De gen. et corr., I, 8, 325a). Aristotle admitted m. in general, or change (μεταβολή, elsewhere κίνησις, Phys., III, 1, 200 b 33 ff., etc.), which is the passage from one mode of being to another: πάσα μεταβολή δότιν ἐκ τινος εἰς τι (ibid., V, 1, 225a 1). He explains it by means of a substratum that assumes various modifications (Met., VIII, 1, 1042 a 32 ff.; Phys., I, 7, 190 a 13). There are three kinds of μεταβολή: from a subject (ὑποκείμενον) to a non-subject (μή ὑποκείμενον), and vice versa; or from subject to subject, namely corruption (φθορά) and generation (γένεσις); and m. in the proper sense, κίνησις, which is continuous m. between two contraries through intermediate states (ibid., V, 225a 8 ff.). With this continuity in mind, Aristotle’s definition of κίνησις can be understood: the act of what is in potency as such: ἡ τοῦ δυνάμει ἔντος ἐντελέχεια, ἡ τοῦτόν (ibid., III, 1, 201 a 10). That is, m. is a perfection that postulates a further perfection. This requirement precisely indicates the passing that is essential to m.: for example, a body moving through point P neither begins to move at P nor ends its m. at P, but comes from a preceding point and proceeds to a subsequent point; thus it is not at P, but passes through P. Aristotle rejects the Zenonian apories, observing that the parts of m. are not actual but potential: “if you make the parts actual, you will not make a continuous m. but will bring it to a halt” (ibid., VIII, 8, 263a 29-30). M. in the proper sense is possible in quality (alteration, ἀλλοίωσις), quantity (increase, αὔξησις, and decrease, φθίας), and position (local m., φόρα; cf. ibid., V, 2, 226a 24-25; H. Bonitz, Index aristotelicus, 449a 50 - b 52).
From m. derive the categories of action and passion: “Motus, secundum quod praedicatur de subiecto in quo est, constituit praedicamentum passionis. Secundum autem quod praedicatur de eo a quo est, constituit praedicamentum actionis” (St. Thomas, In Met., XI, lect. 9, ed. Cathala, n. 2313; cf. Aristotle, Phys., III, 3, 202-213 ff.). In life and knowledge, m. has a more perfect meaning (De An., II, 5, 417 b 2-3).
Local m. is important. Aristotle defined it as essentially relative to place; therefore not even God can produce an absolute m., that is, one not referred to a terminus. This conclusion was proscribed by the archbishop of Paris, Stephen Tempier (1277); hence some later philosophers and theologians admitted an absolute local m., which is an intrinsic change without relation to the terminus. Thus Scotus (Quodl., q. XI; ed. L. Wadding, XII, Lyon 1859, p. 263); G. Buridan (Phys., III, q. 7; ed. Paris 1509, f. 50) and their schools. William of Ockham says that real local m. is possible in relation to a hypothetical terminus (Quodl. VII, q. 6). F. Suárez admits absolute m. as a change of an absolute presence (Disp. Met., dist. 51, sect. 1, n. 21; ed. Paris 1856-61, vol. XXVI, p. 978).
According to Aristotle, local m. is a becoming and therefore requires a mover distinct from the mobile; it is the moving cause and, when the latter no longer reaches the mobile, the “surrounding medium,” which has received the moving force from the mover (Phys., VIII, 10, 267a 2-5). John Philoponus, a commentator of the Alexandrian school, maintains that this moving force, called “impetus,” is instead produced by the mover in the mobile itself (Phys., IV, 8; ed. Vitelli, Berlin 1888, p. 642). Philoponus’s theory was taken up by Francesco de Marchia (IV Sent., princ.) and especially by G. Buridan, who maintained, on the basis of experimental observation, that impetus remains unchanged and therefore that m. lasts indefinitely (Phys., VIII, q. 12; ed. Paris 1509); this is an early indication of the law of inertia. This doctrine became common in later scholasticism (cf. R. Masi, Intorno al movimento locale, in Divus Thomas Plac., 53 [1950], pp. 3-20, 178-208). Descartes states that local m. is translation: “translatio unius partis materiae sive unius corporis ex vicinia eorum corporum, quae illud immediate contingunt et tanquam quiescentia spectantur, in viciniam aliorum” (Princ. Phil., II, 25, ed. C. Adam and P. Tannery, Oeuvres, VIII, Paris 1905, p. 53). For Descartes, local m. is relative and reciprocal: it is an attribute of matter; all the activities of bodies are reduced to local m. (mechanicism); even secondary qualities are produced in us by local m. Moreover, local m. is not a becoming but a state, like the figure of a body, and therefore is preserved indefinitely: thus the law of inertia would be proved (Princ. Phil., II, 27, ed. cit., p. 55).
Characteristic is Newton’s affirmation of an absolute local m., “translatio corporis de loco absoluto in locum absolutum” (Philosophiae naturalis principia mathematica, Amsterdam 1723, p. 6); absolute place, which is itself a part of absolute space (ibid.).
E. Bergson maintains that the intellect decomposes m. in general, or change, into immobile states, as Zeno did. To restore the continuity of change, Aristotle admits a substratum of it (L'évolution créatrice, Paris 1912, pp. 323-53). But intuition reveals what change truly is, pure change: “Il y a des changements, mais il n'y a pas, sous le changement, des choses qui changent: le changement n'a pas besoin d'un support. Il y a des mouvements, mais il n'y a pas d'objet inerte, invariable, qui se meuve: le mouvement n'implique pas un mobile”: La pensée et le mouvement, Paris 1934, p. 185). Pure change is “Duration” (Durée), which is reality itself.
In physics, local m. is essentially relative to the frame of reference; its laws are studied by mechanics.