 The link between reason and happiness is explored at length by Descartes in letters exchanged with Elisabeth during the summer and fall of 1645. The discussion begins with Descartes’ suggestion that they examine what the ancients had to say on the topic, and he chooses as exemplary Seneca’s work “On the Happy Life” (De Vita Beata). Descartes, however, quickly becomes dissatisfied with Seneca’s treatment and proposes instead to explain to Elizabeth how he thinks the subject “should have been treated by such a philosopher, unenlightened by faith, with only natural reason to guide him” (AT IV 263/CSMK 257).