 Descartes’ estimation of the importance of ethics is expressed most clearly in the programmatic statement that prefaces the French translation of the Principles of Philosophy (1647). Here he presents his conception of philosophy in strikingly traditional terms: “the word ‘philosophy’ means the study of wisdom, and by ‘wisdom’ is meant not only prudence in our everyday affairs but also a perfect knowledge of all things that mankind is capable of knowing, both for the conduct of life and for the preservation of health and the discovery of all manner of skills” (AT IXB 2/CSM I 179). The key to the attainment of this wisdom, Descartes argues, is the recognition of the essential order among the different parts of our knowledge, an order he depicts in his image of the “tree of philosophy”: “The roots are metaphysics, the trunk is physics, and the branches emerging from the trunk are all the other sciences, which may be reduced to three principal ones, namely medicine, mechanics and morals” (AT IXB 14/CSM I 186). Within this scheme, metaphysics is foundational, but this knowledge and the knowledge of physics that is built upon it are sought for the sake of the practical benefits that follow from the sciences of medicine, mechanics and morals: “just as it is not the roots or the trunk of a tree from which one gathers the fruit, but only the ends of the branches, so the principal benefit of philosophy depends on those parts of it which can only be learned last of all” (AT IXB 15/CSM I 186). Foremost among these sciences is 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” (ibid.). It is for the sake of this science above all that Descartes hopes his readers will “realize how important it is to continue the search for these truths, and to what a high degree of wisdom, and to what perfection and felicity of life, these truths can bring us” (AT IXB 20/CSM I 190).