To refer to Prince Andrei as a rational man seems to flout Tolstoian psychological theory. In a passage from the second (unpublished) part of Youth that Boris Eikhenbaum treats as autobiographical, Tolstoi explains that one of his earliest maxims arose from a refutation of Descartes's "I think, therefore I am."I recall that the basis of my new philosophy was that man consisted of body, feelings, reason and will, but that the essence of the soul was will, not reason: that Descartes, whom I had not read then, in vain had said Cogito, ergo sum, because he had thought because he had wanted to think. Consequently it was necessary to say Volo, ergo sum.Tolstoi alters Descartes's maxim to make it consistent with the metaphysical underpinnings of science and psychology as he understands them. Life is self-propelled motion, while reason is the principle that defines it or, as he puts it in the second epilogue of War and Peace, gives it form. The essence of a living being, therefore, must be desire or impulse, not thought, which gives form to impulse but does not itself move. To live is to will, not to think.