Note 230 — Chapter XX · (continued 2)

One of the rules Descartes lays down in his posthumous art of logic, is that we ought never to busy ourselves except about objects concerning which our understanding appears capable of acquiring an unquestionable and certain knowledge, vol. xi., p. 204. This is at least too unlimited a proposition, and would exclude, not indeed all probability, but all inquiries which must by necessity end in nothing more than probability. Accordingly, we find in the next pages, that he made little account of any sciences but arithmetic and geometry, or such others as equal them in certainty. “From all this,” he concludes, “we may infer, not that arithmetic and geometry are the only sciences which we must learn, but that he who seeks the road to truth should not trouble himself with any object of which he cannot have as certain a knowledge, as of arithmetical and geometrical demonstrations.” It is unnecessary to observe what havoc this would make with investigations, even in physics, of the highest importance to mankind.