The Traité de l'homme was first published in its original French by Clerselier (L'homme, 1664), after being published in a Latin translation by Florent Schuyl (1619–69) (De homine, 1662 and 1664). Apart from a short summary in the Passions of the Soul (art. 7–16) and the equally posthumous Description of the Human Body, this work is the main source of Descartes’ physiology. A “treatise on man” was planned by Descartes as early as 1629, as part of an explanation of “all natural phenomena, that is, all of physics” (AT I 70, CSMK 7), as indicated by the summary of the “treatise on light” in the Discourse on Method. According to that summary, the treatise would contain a discussion not only of celestial and terrestrial bodies but also of man “because he observes them” (AT VI 42, CSM I 132). Not only is the inclusion of “human nature” in accordance with the traditional conception of physics, but it also matches Descartes’ statement in 1645 that he started work on a “treatise on animals” (which is clearly what we now know as his Treatise on Man) “more than fifteen years ago” (AT IV 326).

Descartes’ approach raised the challenging problem of how to integrate a theory of man into his own theory of nature, given the fact that the human mind cannot be reduced to matter; and he could not speak of living bodies “in the same manner as the other things, that is, by demonstrating effects from causes and showing from what seeds and in what manner nature must produce them” (AT VI 45, CSM I 134). The first problem could be solved by giving the human mind an exceptional status; the second problem could be solved only by means of the “supposition” that “God formed the body of a man exactly like our own … using for its composition nothing but the matter that I had described,” without placing in it