Descartes wrote little in the way of moral philosophy, but he regarded the topic as of the utmost importance. As he describes it in the preface to the French edition of his Principles of Philosophy, the uppermost branch of the tree of philosophy is occupied by la morale, “the highest and most perfect moral system, which presupposes a complete knowledge of the other sciences and is the ultimate level of wisdom” (AT IXB 14/CSM I 186). This moral system would be more than just the final element of Descartes' philosophy; it also defines the end, or telos, of his ordered reconstruction of knowledge. In an important sense, the prior, theoretical parts of his philosophy are established for the sake of the practical benefits that follow from them. To those skeptical about what philosophy has to offer, Descartes confidently replies that the difference between his principles and those of other philosophers, “as well as the long chain of truths that can be deduced from them, will finally make them realize how important it is to continue in the search for these truths, and to what a high level of wisdom, and to what perfection and felicity of life, these truths can bring us” (AT IXB 20/CSM I 190).

Descartes is usually seen as the quintessential modern philosopher, yet in his broader conception of philosophy's goal we find repeated a central ancient theme: philosophical knowledge is valued not only for its own sake, but as the basis of the best sort of human life – one in which we realize the greatest perfection and happiness.