No one has portrayed better the deep and powerful skepticism that prevailed during the sixteenth and seventeenth centuries, especially in France, in the fields of science, mathematics, and religion than Richard Popkin. Religious persecution was rampant, and epistemology was “a new machine of war.” Given the extreme doubt regarding so many matters, confidence in the possibility of knowledge was low, at best. This was the skepticism that Descartes tried desperately to combat. He wanted to combat it by showing that there was, at least, one certainty on which an entire edifice of knowledge could be constructed. That certainty was such that it could not be doubted, no matter how deep and sweeping the doubt that the human mind could invent. On that certainty, the confidence in human reason could be regenerated. So Descartes thought.

In this matter, Descartes nicely contrasts with Saint Augustine. Here is Saint Augustine in De Utilitate Credendi: “I could produce many arguments to show that absolutely nothing in human society will be safe if we decide to believe only what we can regard as having been clearly perceived” (CSM II, 152; AT VII, 217). By contrast, Descartes' revolution of reason was designed to show that nothing would be safe if we decided otherwise – neither society, nor knowledge, nor for that matter faith. “I am vain enough to think,” he said, “that the faith has never been so strongly supported by human arguments as it may be if my principles are adopted” (CSMK, 88; AT I, 564).