“DESCARTES, a whole lifetime after the beginning of the Reformation, set out to begin if he could, the whole thing [philosophy] over again—to ask and settle all those questions which scholastic philosophy had also examined from the very roots. He even started with the discussion as to whether man himself, the mind originating the discussion, existed or no. He took as his starting point the undoubted truth that since man thinks, he “is”; and on that he would base his system. In the expansion of that system he insists upon only accepting knowledge that is “proved,” and that is where he had so great an influence upon all the thought which followed for three hundred years; for all the modern scientific habit until yesterday proceeded from Descartes. He himself had no doubts upon the Faith, but his insistence upon the axiom that our acceptation of truth must depend upon the external proof of it or upon deductive reasoning from observed constant natural “laws” did make profound inroads upon ordinary belief. It was from this attitude of mind that all that is called the “rationalistic” attack upon the Faith has ultimately grown.”
~Hilaire Belloc: Characters of the Reformation, Chap. 1.