Causality

René Descartes (1596–1650) distinguished all substances into two sorts: thinking things (res cogitans) and extended things (res extensa). He took the essence of mind to be thought and that of matter extension. Unlike Aristotle, he thought that matter was inert (since its essence is that it occupies space). Yet, there are causal connections between bodies (bits of matter) and between minds and bodies (bits of different substances). So, two big questions emerge within Cartesianism. The first is: how is body-body interaction possible? The second is: how is mind-matter interaction possible? Descartes's answer to the first question is the so-called transference model of causality: when x causes y, a property of x is communicated to y. He thought that this view is an obvious consequence of the principle "Nothing comes from nothing." As he put it: "For if we admit that there is something in the effect that was not previously present in the cause, we shall also have to admit that this something was produced by nothing" (vol. 1, p. 97). But Descartes failed to explain how this communication is possible. Indeed, by taking matter to be an inert extended substance, he had to retreat to some external cause of motion and change. Descartes treated forces with suspicion since they did not quite fit within his tight scheme of the two distinct substances and their two essential attributes. So in his Principles of Philosophy (1644) he retreated to God, whom he took to be "the efficient cause of all things" (vol. 1, p. 202). But this retreat to God cannot save the transference model. Besides, the transference model of causality makes an answer to the second question above (how do mind and matter interact?) metaphysically impossible. Being distinct substances, they have nothing in common that can be communicated between them. Descartes was a rationalist. He thought that Reason alone can, by a priori reflection, discover the basic casual laws of nature, which, Descartes thought, stem directly from God.