Page:A Brief History of Modern Philosophy.djvu/64

Rh act of naming. But this act is subject to certain conditions even from its very beginning; it is not permissible therefore to give two contradictory names to one and the same thing.

That all change consists of motion (mutationem in motu consistere) is therefore the most general principle of science. Hobbes thinks that, if we should only rid ourselves of all prejudices, the proof of this principle is wholly superfluous. He assumes several other, purely dogmatic, principles, without inquiring more closely into their respective conditions; the law of causation, the principle of inertia, the principle that only motion can be the cause of motion, and that only motion can be the result, and the principle of the persistence of matter.

If these principles are to explain all existence, then everything must be motion. The classifications of the system are therefore based on a classification of motion. First in order comes the theory concerning the Corpus (body in general); here he treats of the geometrical, mechanical and physical laws of motion. The second part contains the theory of the Homo, i.e. the motions which take place in Man; here the physiological and psychological motions are treated. The third part is the doctrine of the Cives, i.e. of the motions in men which condition their mutual relations and their association.

Hobbes was unable to complete his system by purely deductive processes. He was forced to concede the necessity of introducing new presuppositions at a number of points. Thus, e.g. when we pass from geometry to mechanics: Hobbes grants, that a pure geometrical explanation rests on an abstraction, and that we must assume the concept of energy (conatus, impetus) at the beginning of mechanics. The same is true when we pass from