A History of Ancient Philosophy by Johansen Karsten Friis; Rosenmeir Henrik;

Author:Johansen, Karsten Friis; Rosenmeir, Henrik;
Language: eng
Format: epub
Publisher: Routledge
Published: 2011-09-11T16:00:00+00:00

DYNAMICS

Aristotle’s combination of immediate observation with speculation is a consequence of his basic position that natural philosophy should presuppose ‘that’ and explain ‘why’—the Aristotelian ‘why’. Broadly speaking, modern natural science has achieved its results by refraining from explaining ‘why’ and by concentrating instead on a description of ‘that’ or ‘how’. Here, as is well known, carefully planned and ordered experiments have been of decisive importance. The arranged experiment has no place in Aristotle’s project in natural philosophy; he does not even find it worthwhile to check what to him were evident, observable facts—which Galileo quite justly criticized in his famous refutation of the Aristotelian theory of the free fall (Galileo, Dialogo sopra i due massimi sistemi del mondo, I 106 ff.). Aristotle’s natural philosophy is an interesting example of how far one, on his presuppositions, could come towards a phenomenological description of nature; but not least the cosmology and the theory of elements reveal the chasm that separates him from modern principles of natural science. Nevertheless, there is one area of physics in which Aristotle—also from the point of view of natural science—was a pioneer, even though his concrete results are unacceptable. This concerns his special theory of motion, dynamics. In the old tradition motion was explained by the principle of ‘like seeks like’ or generalization from the observation of thrusts, pushes, or the like. It follows from Aristotle’s general position that motion is a most complex phenomenon that must be understood as the joint work of several factors. Now, it is one thing that he was ignorant of the law of gravitation, of the difference between gravitational and inertial mass, and of the concepts of acceleration and momentary velocity and that with oddly lop-sided perspicacity he rejected the laws of free fall and of inertia. But it is crucial that he introduced the concept of force as a quantifiable entity in the theory of motion. In agreement with his ideal of science, Plato was concerned with cinematics, which is to say that he wanted to describe motion mathematically. It agrees with Aristotle’s ideals that in his description of motion he introduces the physical concept of force; this opens the way for a quantitative causal explanation, dynamics. Aristotle did not anywhere present dynamics as a separate discipline; yet it is possible to extract a consistent theory.

His special doctrine of motion rests on two basic views that have already been brought up. In part, everything moved is moved by something else; in part, there are three forms of motion: the natural, the compulsive and the voluntary (cf. Phys. 254 b 12 ff.). Voluntary motion is of course special for living beings and defies the possibilities of physical description. The natural motion ‘up’ and ‘down’ is the basic one (De caelo 300 a 23), but most clearly of all the motion by compulsion shows the general principles: here it is evident that the moved is moved by something else; the natural object does indeed have the principle of motion in itself, but motion comes about through some external cause.

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