Causes and Forces in Sixteenth-Century Physics

Abstract

T HE TITLE OF THIS ARTICLE is suggested by a chapter in Annaliese Maier's Die Vorlaufer Galileis im 14. Jahrhundert which she captioned Ursachen und Krafte.I In this she concentrated on the thirteenth and fourteenth centuries and attempted to explain how the Latin terms causa and vis then had meanings that were partly the same as, and partly different from, their modern equivalents. At first sight it appears that the concept of cause is characteristically medieval, whereas that of force is characteristically modern, but from Miss Maier's researches one can see that no such clearcut dichotomy obtains. Indeed, vis was quite commonly used by medievals to designate violent or external causes that force a motion from without; it was also used by them, though less commonly, to designate causes or forces that are operative in nature and that originate motions from within.2 Significantly, for our purposes, this latter use reappeared and was reinforced in the sixteenth century, possibly for the reason that John Philoponus' commentary on Aristotle's Physics, which was published in Latin translation in 1539 and again in 1558, employs a definition of nature that explicitly incorporates the force concept.3 In Aristotle, nature is defined as a principle and cause of motion and of rest in that in which it is