Some of the most innovative and influential natural philosophies of the sixteenth century are

produced by physician-philosophers. They offer a cosmos filled with medical spirits, humors, and

living faculties. Humanist medicine represented the avant-garde of natural philosophy, where the

Neoplatonic, Stoic, and Paracelsian came to mix with more conservative currents of Aristotle and

Galen. Surprisingly, history of science has hardly asked about the role that humanist medicine

played in the development of new physical principles. I confront one of the most extraordinary

characteristics of such medical-vitalist philosophies: they dissolve Aristotelian borders and offer

universal forces acting and circulating through all of space.

In order to capture the medical turn, I will focus on two of the sixteenth century's foremost

physician-philosophers: Jean Fernel (1497-1558) and Girolamo Cardano (1501-1576). I will offer

the first systematic exploration of their natural philosophies, and of the medical ideas therein. My

project will then create a bridge to the Scientific Revolution by considering William Gilbert (1544-

1603) and Johannes Kepler (1571-1630). These two early Copernicans drew extensively from

medicine and from medical-vitalist philosophies. Gilbert was himself a highly influential physician.

My project will explore the medical concepts and methods at play in Gilbert's "magnetic"

philosophy and in Kepler's work to understand the mathematical forces of heaven and earth.