which He has created being capable of changing its state without some external cause contradicts this immutability. Material things cannot therefore on their own account (sua sponte) without external interference (of another material thing) pass from motion to rest or vice versa. (Descartes nevertheless makes a reservation in the interest of his spiritualistic psychology, namely that it is perhaps possible for souls or angels to act on matter.) Besides inertia, Descartes likewise deduces the constancy of motion (an imperfect antecedent to the persistence of motion) from the unchangeableness of Deity. Conservation (which, according to Descartes, consists of an incessant continuance of creative activity) implies that the sum total of motion implanted in matter at creation must remain unchanged. The distribution of motion among the various parts of the universe may vary, but no motion can be lost and no absolutely new motion arise.
Descartes regards the teleological explanation of nature, which accounts for natural phenomena from the viewpoint of ends, as inapplicable. He bases his rejection of final causes on theological grounds. Since God is an infinite being, he must have purposes beyond our power to conjecture, and it were therefore presumption on our part to suppose it possible to discover the purposes of natural phenomena. There are likewise many things in the finite universe which do not affect us in the least,—what sense could we therefore ascribe to their having been created on our account!—The teleological explanation is therefore rejected, because it is too narrow.
Descartes undertakes a detailed explanation of nature on the basis of the principles thus established. He differs from Bacon at this point in the importance which he attaches to deduction, and from Galileo (whose importance