In this Reply, I respond to Michael Nauenberg’s single major contention that in my recent AJP article1 I misinterpret Newton’s passage on the meaning of the Principia’s Law 2.
In an unpublished passage composed in the early 1690s, Newton describes the meaning of the Principia’s Law 2 in the language of deflections.2 He begins by considering a given body in motion at A that would have gone on to traverse the segment Aa, had its speed and direction at A been uniformly continued for a given time increment h. An impressed force (that is, a specific “thrust” or “pull”) at A deflects the body from that inertial motion and makes the body describe instead the arc Ab in that same time increment h. The impressed force thus generates the deflection . Newton draws Fig. 1 to illustrate the situation....
