Modesty was not a condition from which Descartes suffered. — Russell Shorto

The situation in biology was particularly complex. Biologists craved the sort of base principles that Newton had developed for physics. Trying to classify life-forms begged the question of what overall purpose you had in mind. The system that was still largely in effect in the early nineteenth century was the “teleological taxonomy” created by Aristotle and refined by the Scholastic philosophers: the “scale of beings” system, which the French called the série, or series, and which is popularly known as the “great chain of being.” As with the medieval system of bodily humors, it was far more complex and useful than its popular stereotype suggests, but it had a serious limitation, which was its teleological basis.

If the West is heading toward some kind of crisis, it’s worth asking ourselves a few basic questions. Modern society as we normally define it—a secular culture built around tolerance, reason, and democratic values—occupies a rather small portion of the world, and there are signs that it is shrinking. Is modernity the inexorable force of progress that we tend to assume? Is it a mere moment of human history that is fast fading? If it is something to value, how can we rediscover it, separate the good and the bad in it, make it relevant and vital?

The irony is that in shifting the focus onto the individual human mind, which everyone agrees can be a pretty flimsy and wayward organ, Descartes had arrived at the closest thing to a certain basis for knowledge. If my own thoughts are the only indubitable ground I can stand on, apparently they aren’t so flimsy after all, at least not all the time. As an earlier follower of Descartes put it, “doubt is the beginning of an undoubtable philosophy.” Therefore the mind and its “good sense”—that is to say, human reason—are the only basis for judging whether a thing is true. With the “cogito,” as philosophers abbreviate it, and with the theory of knowledge that arises from it, which Descartes outlined in the Discourse on the Method and later works, human reason supplanted received wisdom. Once Descartes had established the base, he and others could rebuild the edifice of knowledge. But it would be different from what it had been. Everything would be different.