Page:Mind (New Series) Volume 8.djvu/364

 350 ROBERT LATTA: Again motion, according to Spinoza, is an infinite mode, that is to say, it is an immediate modification of the attribute of extension, " following from the absolute nature of that attribute "- 1 But he makes no attempt to show how motion " follows from the absolute nature" of extension. All that he can really mean is that motion presupposes extension. Motion is the stepping-stone between finite bodies and the infinite attribute. The differences of finite bodies all pre- suppose (or are reducible to terms of) the motion of particles, this motion of particles as a totality presupposes (when we think away the finite element in it, the parts or particles) an infinite motion, which similarly presupposes extension, which in turn presupposes substance. Each stage is obtained from that which preceded it by the removing of certain determina- tions, until we reach the " absolutely indeterminate ". 2 Now the characteristic feature both of Descartes's and of Spinoza's view is the negative form in which the relation between extension and motion is regarded. According to Descartes, motion comes to extension entirely ab extra : according to Spinoza, motion, being a mode, presupposes extension, but extension, being an attribute, must be conceived through itself alone and is therefore independent of motion. Hence, when Descartes takes it as the fundamental principle of his laws of motion that the quantity of motion and rest in the universe (or in any isolated system of bodies) is fixed and unchangeable, he leaves out of account the direction of motion, because that is a quality not of motion per se but of motion in space. Further it is interesting in this connexion to recall the fact that Leibniz on his journey to Holland to visit Spinoza wrote a paper on the principle of motion, and that one of the few things he tells us about his interviews with Spinoza is that " Spinoza did not quite clearly see the defects of Descartes's laws of motion : he was surprised when I began to show him that they were inconsistent with the equality of cause and effect ". 3 Now Leibniz's objection to Descartes's laws of motion is that they are too abstract. Motion, of course, mathematically considered, must be an abstraction ; but motion regarded as something given quite independently of extension is motion considered more ab- stractly than is necessary. In fact motion and extension mutually presuppose one another : they are both abstractions from one reality. This might be illustrated by the fact that 1 Eth., I, 21; cf. Ep. 64, Van Vloten (66 Bruder). 2 Ep. 36, Van Vloten (41 Bruder). 3 Foucher de Careil, Refutation inedite de Spinoza, p. Ixiv.