Galileo's concept of inertia / Josè Alberto Coffa.
Abstract:
This paper presents a discussion of the 'circularist' thesis, according to which Galileo held (explicitly or implicitly) a principle of circular inertia. Possible interpretations of this claim are considered and later on contrasted with the available evidence. It is shown that circularists have failed to pay due attention to the fact that in Newtonian mechanics inertial motion is predicated of force-free systems. The obvious rejoinder that an appeal to the notion of freedom of external forces would be anachronistic is seen to be unjustified, since a careful analysis of Galileo's work shows that he was looking for the properties of what in post-Galilean terminology can be described as force-free systems. When account is taken of several methodological as well as sociological issues, it turns out that Galileo's inertial views are much closer to Newton's than is now generally acknowledged
Physis A. 10, fasc. 4 (1968), p. 262-281