Descartes' Thoughts On Reality

He writes that no finite substance can come to be "without being created by God"; also, using a stone as his example. He says that a substance is "a thing capable of existing of itself." This may appear to be a contradiction, but he explains more carefully, "By substance, we can understand nothing else than a thing which so exists that it needs no other thing in order to exist." However, he adds that realities being independent of everything except God for their existence.

Descartes is a metaphysical dualist in the sense that he analyzes all reality in terms of two irreducible categories of substances. He denies that we can "observe more than two ultimate classes of real things -the one is intellectual things, or those of the intelligence, that is, pertaining to the mind or to thinking substance, the other is material things, or that pertaining to extended substance, i.e., to body."

Descartes writes, "There are various degrees of reality or being: a substance has more reality than an accident or a mode; an infinite substance has more reality than a finite substance." So, he holds a Neoplatonic sense of hierarchy of reality.

He offers us an example of what he means by comparing philosophy to a tree, "Thus philosophy as a whole is like a tree whose roots are metaphysics, whose trunk is physics, and whose branches, which issue from this trunk, are all the other sciences. These reduce themselves to three principal ones, viz, medicine, mechanics and morals."