The Life of Reason by George Santayana — Read

Mechanism restricted to one-half of existence.

When Democritus proclaimed the sovereignty of mechanism, he did so in the oracular fashion proper to an ancient sage. He found it no harder to apply his atomic theory to the mind and to the gods than to solids and fluids. It sufficed to conceive that such an explanation might be possible, and to illustrate the theory by a few scattered facts and trenchant hypotheses. When Descartes, after twenty centuries of verbal physics, reintroduced mechanism into philosophy, he made a striking modification in its claims. He divided existence into two independent regions, and it was only in one, in the realm of extended things, that mechanism was expected to prevail. Mental facts, which he approached from the side of abstracted reflection and Platonic ideas, seemed to him obviously non-extended, even when they represented extension; and with them mechanism could have nothing to do. Descartes had recovered in the science of mechanics a firm nucleus for physical theory, a stronghold from which it had become impossible to dislodge scientific methods. There, at any rate, form, mass, distance, and other mathematical relations governed the transformation of things. Yet the very clearness and exhaustiveness of this mechanical method, as applied to gross masses in motion, made it seem essentially inapplicable to anything else. Descartes was far too radical and incisive a thinker, however, not to feel that it must apply throughout nature. Imaginative difficulties due to the complexity of animal bodies could not cloud his rational insight. Animal bodies, then, were mere machines, cleancut and cold engines like so many anatomical manikins. They explained themselves and all their operations, talking and building temples being just as truly a matter of physics as the revolution of the sky. But the soul had dropped out, and Descartes was the last man to ignore the soul. There had dropped out also the secondary qualities of matter, all those qualities, namely, which are negligible in mechanical calculations. Mechanism was in truth far from universal; all mental facts and half the properties of matter, as matter is revealed to man, came into being without asking leave; they were interlopers in the intelligible universe. Indeed, Descartes was willing to admit that these inexplicable bystanders might sometimes put their finger in the pie, and stir the material world judiciously so as to give it a new direction, although without adding to its substance or to its force.