Yet Descartes saw his skepticism as constructive rather than destructive: those bits of knowledge which survived it would be certain, and would be the unshakable foundation stones for a new philosophical system. Russell Shorto writes:
It was necessary for him to prove both the existence of God and the innate goodness of God, for, given the corrosiveness of Cartesian doubt, these were the only assurances we have that the material world really exists. So his work has a theological grounding: not only do the world and science depend on God, but so does Cartesian philosophy.
If chemistry and physics are to bring us any knowledge, Descartes writes, it will be upon this basis: for him, the “divine spark” may be characterized as certainty. One of his followers, Nicolas Malebranche, would refine this theme:
To talk of Cartesian dualism is somewhat misleading; Descartes actually wrote that the universe consisted of not two but three substances: mind, body (that is, the material world), and God. God is the guarantor that the mind and the world can interact meaningfully - that we can reach truth using the power of reason.
Malebranche doesn’t seem to realize that his insight into Cartesian thought has an odd resemblance to Plato’s tripartite soul, and Shorto, in summarizing Malebranche’s view, doesn’t point out the same similarity to Freud’s tripartite mind. The central role of God in Cartesian thought translates into the central role of God in modern philosophy:
It would be wrong to imagine that the Enlightenment was antireligion. Its mainstream thinkers, as well as many if not most of the radicals, were antichurch, not antifaith. Their problem with religion was that it kept individual humans from exercising their own minds and applying their innate reason to understanding the world and their place in it. This criticism applied not only to Catholicism but also to Protestant theology.
Here Shorto relies on the somewhat sloppy shorthand of “Enlightenment” for “modern philosophy” or for “thinkers writing in era immediately after the death of Descartes.” The notion of the “Enlightenment” as a distinct historical era, even if we allow for some variations within the monolith, is so ambiguous as to be undefinable. But the point stands: there was an eager engagement in the concept of God, even as there was a violent rejection of institutionalized religion. Spinoza exemplifies this:
Spinoza insisted that there is such a thing as religious truth, but he also insisted that religious institutions were largely concerned with protecting their own position.
Descartes, who agreed with Aristotle very rarely, might have formulated the matter in terms of an Aristotelian golden mean: a healthy skepticism, even a bitter cynicism, about religious institutions does not entail a rejection of the concept of God. On the contrary, our assumption that the universe behaves in an orderly fashion (the laws of chemistry and physics) implies a theistic view.
