The state of European knowledge at the beginning of the seventeenth century was peculiar. Remarkable advances had already been achieved, the tide of inquiry flowed as strongly as at any other period in our history, and the fruitfulness of the presuppositions which inspired this inquiry showed no sign of exhaustion. And yet to intelligent observers it appeared that something of supreme importance was lacking. The state of knowledge, wrote Bacon, is not prosperous nor greatly advancing. And this want of mind hostile to the sort of inquiry that was on foot; it was observed as a hindrance suffered by minds already fully emancipated from the presuppositions of Aristotelian science. What appeared to be lacking was not inspiration or even methodical habits of inquiry, but a consciously formulated technique of research, an art of interpretation, a making good this want was the occasion of the unmistakable emergence of the new intellectual character I have called the Rationalist. The dominating figures in the early history of this project are, of course, Bacon and Descartes, and we may find in their writings intimations of what later became the Rationalist character.