Descartes was a geometrician. He found only in mathematics and geometry the certainty that he required. Therefore, he used the methods of geometry to think about the world. Now, in geometry, one begins with a search for axioms, simple undeniable truths – for example, the axiom that a straight line is the shortest distance between two points. On the foundations of such “self-evident” propositions, whole geometrical systems can be built. Following his geometrical model, Descartes proceeds to doubt everything – de onmibus dubitandum. He will suspend belief in the knowledge he learned from childhood, all those things “which I allowed...