Descartes:00020

In a letter of June 1643 (AT 3, 692–3; CSMK, 227) Descartes tells Princess Elisabeth that, as a rule, he spends only a few hours a year thinking about metaphysics, while he devotes some hours each day to thoughts on mathematics and on the shapes and motions of bodies. We should certainly take the letter seriously: the greater part of Descartes’ opus is indeed scientifically oriented. Think only of the Essays, of the bulk of the Principles, of the various unfinished works, for example on embryology. It happens that, in its detail, Cartesian science is now merely of historic interest – say, the pronouncement in article 65 of Part 4 of the Principles (AT 8a, 245) that water flows on earth as blood does in our body, in a circle from mountains down to the sea in what we call “rivers,” and then back to the mountains again, in subterranean ducts.