The most perplexing aspect of Galileo's work in physics is without doubt the sharp distinction one can draw between his essentially dynamic studies in such juvenilia as De Motu and the consciously kinematical approach of his later output—particularly the Two New Sciences. Whether one chooses to call this a shift from the “why” of motion to the “how”, or, as I should prefer, a shift from dynamics to kinematics, there can be no denying its existence. The Galileo who wrote that (...) “The present does not seem to be the proper time to investigate the cause of the acceleration of natural motion …” is, on the face of it, a very different man from the one who had earlier written almost an entire treatise on precisely this topic. (shrink)