Our sixteenth-century physician-philosopher, Jean Fernel, supposed in the body a something incorporeal. The material body did not work itself. The body was tenanted by a principle which made it ‘live’. In respect of the acts of the body the corporeal substance of the body was as a tool in the hand of a craftsman, the craftsman being that incorporeal tenant of the body. Fernel supposes this not only of man but of animate creation generally. In other words, there is throughout animate Nature a living principle which informs its bodies with life.

This living principle and its activities in the body, Fernel now proceeds to describe. His description purports to be a description of the principle. But the principle is incorporeal substance; it offers beyond that no data for description. We have seen already how when calling it in Aristotle's sense ‘form’ Fernel has settled that it is non-elemental heat, and has derived it from beyond the stars. The description he embarks on now resolves itself into an account of what it does, this principle of life, which has the body for its field of operation.