The Assayer ofGalileoGalilei is a classic of Italian literature. The Assayer was written in the context of the discussion on comets, and responds, word by word, to the Libra astronomica ac philosophica firmed by Lotario Sarsi but written by Orazio Grassi. From the formal (i.e. rhetorical) point of view The Assayer is an example of the judicial, defensive speech. Nevertheless, in the book one can notice the presence of the epideictic speech, as well. The epideictic speech prises the methodological values proper to the Copernican vision
of the universe and blames those involved in the Aristotelian and Ptolemaic approaches. There is in The Assayer a very famous rhetorical period — the one ending with the proverbial aut Caesar aut nihil — in which the internal connection between both types of speeches can be analysed. The rhetorical exercise developed in the present essay tries to disentangle the complex node of these speeches in the above mentioned fragment.