  The second problematic aspect of Descartes’s rationalism is more difficult to resolve. Descartes was a radical voluntarist who thought that all truth, including what we take to be necessary truth, depends on the will of God. Care needs to be taken in how this view is expressed, for Descartes did not hold simply that what we take to be necessary in fact is contingent. He held that actually necessary truth depends on God’s unconstrained will, such that even propositions that are logically contradictory might have been simultaneously true. Reason itself thus seems no longer reliable, and experience would seem to be the only way of determining which of the worlds even beyond logic such a powerful and unconstrained God has created. Not many of the rationalists, even among the Cartesians, followed Descartes in this radical voluntarism, and some in recent times have seen the view as ultimately incoherent. Even so, Descartes seems to have taken the view as the basis at least of his physics, and perhaps of his whole system. Indeed, on some accounts, it was this doctrine of created truth that enabled Descartes to frame the most radical doubt hitherto conceived, when in the Meditations he entertained the possibility that he was always deceived by a mendacious deity, even when considering what appeared to him most obviously true, to wit, the existence of the “simplest things” that are the subjects of arithmetic and geometry. (Against this view, Margaret Wilson (1982, 105–114), observes that, in Meditation 1, God need only have the power to deceive me about the eternal truths, not to create them.) While a doubt (and a doctrine) this radical might lead one to despair of ever achieving sure knowledge, for Descartes, it was the catalyst for his discovery of the cogito, and with it, his first indubitable truth—the truth of his own existence.