HOW DESCARTES'S PROJECT DIFFERED

John Locke, after distinguishing sharply between knowledge, on the one hand, and belief (opinion, assent) on the other, proceeded to offer a general ethic for the governance of our belief. “Reason must be our last judge and guide in everything,” he said (IV,xix,14). Or more illuminatingly: Assent, “if it be regulated, as is our duty, cannot be afforded to anything, but upon good reason … For he governs his assent right, and places it as he should, who in any case or matter whatsoever, believes or disbelieves, according as reason directs him” (IV,xvii,24). We have seen that it is to all and only matters of maximal “concernment” that these ringing affirmations were meant to apply.

That there is a general ethic of belief, and that in this ethic Reason has a central role – once these convictions had been clearly formulated and persuasively propounded by Locke, they became prominent in the mentality of modernity. In that mentality, Locke's view as to the content of that ethic, and the proper role of Reason therein, became classic: For any proposition of maximal “concernment” which is not intuitively or demonstratively known to be true, Reason is to determine the probability of the proposition on satisfactory evidence, and we are to place a level of confidence in the proposition proportioned to what Reason tells us is that probability.