Jean-Luc Marion sees a fateful change in theology proper when Descartes describes God as “causa sui” rather than as “uncaused cause” (which was the scholastic description).
What’s the deal? Marion says that talking about a self-caused God makes no sense. As John Caputo summarizes the point: “It makes no sense to say that God can do things that make no sense, not when God is the very height of sense and meaning and truth. It pays God no real compliment. It makes much more sense to say that nothing is the cause of God, that God is the first cause of everything else but God himself is uncaused, that God exists in and of himself, as pure and sheer eternal necessity, without beginning or without end.”
If this is so, what does Descartes gain by talking about God as self-caused? Caputo again:
“Descartes wanted a world that was thoroughly rational, and for him that meant one that obeyed in every respect the axioms that reason lays down, in which the principles of reason held pride of place. The world is the sphere of things that meet the demands of reason, that pass muster under the inspection that reason makes, that are are able to present their papers in order to be allowed to cross the border from fiction to reality. As a mathematician and a physicist, for example, Descartes said that, much as we love the odors and colors and feels of physical objects, as strictly rational beings we have to give them up and concede that the only thing that is ‘really out there,’ ‘objectively’ (this was an entirely new way to talk) is mass and velocity, while such pleasant things as blue or sweet are strictly subjective or private sensations. Why so? Because the measure of physical reality is what is mathematically measurable, and the only thing you can measure about ‘blue’ is light waves, or about ‘loud’ is the frequency of sound waves. Reason does not take what is out there on face value and then adjust to it. On the contrary, by reason we mean the authority to determine what is out there in the first place and to set the standards to which things have to measure up.”
To speak of God as “causa sui,” then, was a way of emphasizing the objective reality of God. Since everything is caused, then God too has to be caused if he’s not going to be fictional. Causa sui might seem a statement of divine sovereignty; but it actually assumes, on Marion’s argument, the sovereignty of reason. Caputo again:
“What is eternally necessary and unconditional is reason, and if God is going to get a share in all that glory, it will be because God measures up to the principles and standards reason sets. Of course, for Descartes and for most early modern thinkers, God does. God passes all these tests summa , nay maxima cum laude . God scores perfectly on all of reason’s tests. The statement ‘God exists’ is true because God meets the standards reason sets for a statement to be true. Descartes was a completely orthodox Catholic with no interest in overthrowing the substantive conclusions of classical theology. Instead, Descartes was interested in proofs and method and setting things out with the fixity and surety of mathematics itself; that is what is revolutionary about his thinking. God meets all the standards reason sets, including the principle of causality . God is the cause of himself, because everything has a cause - and reason cannot give in on that point, cannot give up one of its principles - including God, who is uniquely cause of himself.”