The disciplinary demarcations of the early modern period were such that investigations and speculations on body and the physical world were legitimate concerns not just of those one would now describe as scientists, but of most of the philosophical community. The Peripatetic tradition was the intellectual framework within which most seventeenth-century philosophers were educated and within which many of them pursued their philosophical careers. The doctrine of hylemorphism (hyle, matter, morphe, form or shape) was central to Peripatetic philosophy. In Physica I, Aristotle taught that there are three principles of natural things: prime matter, form, and privation. Natural body is the concern of natural philosophy. Peripatetic writers like Abra de Raconis and Johannes Magirus considered the object of physics to be natural/mobile body. All proponents of the mechanical philosophy shared the Peripatetics' view that physical body requires impenetrability as the necessary concomitant of its mere extendedness in three dimensions.