The clash between Galileo and the Catholic Inquisition has been discussed, studied, and written about for many decades. The scientific, theological, political, and social implications have all been carefully analysed and appreciated in all their interpretative fruitfulness. The relatively recent trend in this kind of scholarship however seems to have underestimated the fact that Galileo in this debate, as in his earlier debates, showed a particular style marked by overconfidence. If we keep in mind the Lakatosian account of scientific development, (...) it is of course perfectly understandable that scientists at times stick to their convictions by producing auxiliary hypotheses as buffers against contrary evidence. And elements of this are detectable in the arguments of both Galileo and his opponents. But one still needs to ask: To what extent did Galileo depend on auxiliary hypotheses? How insecure did they render his position? And how ad hoc were they? These are important questions because Galileo’s particular way of dealing with auxiliary hypotheses can throw light on the broader question of when and how auxiliary hypotheses are needed within scientific practice in general. It can even indicate some way of conceiving degrees of ad hocness. In this paper, I explore this issue by comparing two important debates in which Galileo was involved: one about the nature of water and buoyancy, the other about cosmology. I revisit not only the scientific content of these debates but also the cultural context in which they took place, especially their dependence on patronage and their theological repercussions. The results indicate that scholarship on Galileo can still be useful in clarifying currently relevant aspects of scientific practice, and is thus still far from its expiry date. (shrink)