 Momentous figures living in momentous times are full of interpretive fecundity, and Galileo has been the subject of manifold interpretations and much controversy. The use of Galileo’s work and the invocations of his name make a fascinating history (Segre 1991; Palmerino and Thijssen 2004; Finocchiaro 2005; Shea and Artigas 2006), but this is not our topic, which are the philosophical implications of his work.