 In his letters to Elisabeth of 1645 and 1646, Descartes develops his moral philosophy, and in particular, his account of virtue as being resolved to do that which we judge to be the best. His letters begin as an effort to address a persistent illness of Elisabeth, which Descartes diagnoses as the manifestation of a sadness, no doubt due to the events of the English Civil War. As Elisabeth herself puts it, he “has the kindness to want to cure [her] body with [her] soul” (AT 4:208, 24 May 1645). While they begin by reading Seneca’s De Vita Beata, they both agree that the work is not sufficiently systematic, and discussion turns to Descartes’s own views. Once again, Elisabeth, in her letters, plays a principally critical role.