Much contemporary transhumanist thought is built on the early modern distinction between nature and thought. A compound of the key terms phusis (“nature”) and logos (ordered “thought”), this chapter investigates the evolving use of the term physiologia (“physiology”) from Antiquity to the early modern period. In the first part of his 1554 medical textbook entitled, the French physician Jean Fernel[aut]Fernel, Jean (generally credited as the first to use “physiology” in a medical sense) defines the term as the “natural contemplation concerning the human,” drawing on a Platonic use of the term “contemplation.” In his 1655 translation of Fernel’s[aut]Fernel, Jean Physiologia, the Parisian physician Charles de Saint-Germain renders the phrase the “knowledge of the natural composition of the human,” effacing the tensions present in Fernel’s[aut]Fernel, Jean phrase. This chapter argues that Saint-Germain’s apparent mistranslation reflects a more fundamental change in the way the notions of “nature” and “thought” are conceptualized in the early modern period. By modifying Fernel’s definition in his translation, Saint-Germain separates thought from nature, bringing Fernel into line not only with the functional physiology of William Harvey[aut]Harvey, William but also with nascent Cartesian philosophy.