ABSTRACT
An additional obstacle is related to the very notion of a theorem, because Aristotle sometimes uses the term theorema, but never in the sense of a mathematical theorem. Therefore the concepts of a ‘theorem’ and of a ‘proof of the theorem’ were probably developed only after Aristotle. That means, in turn, that the mathematical meaning of theorema did not appear before the last decades of the fourth century, when, indeed, there was a vast mobilization of mathematicians engaged in identifying and proving such theorems – culminating of course in the work of Euclid. From this it is permitted to infer that to attribute an interest in mathematical theorems to Thales is sensationally anachronistic. Indirect confirmation of what the author have just observed emerges, somewhat surprisingly, from a famous passage of Aristophanes’ Birds.
