 The reasons which Protagoras reportedly adduced in support of his thesis—the obscurity of the problem and the brevity of human life—have been regarded as too banal, or at any rate not particularly relevant. However, they acquire greater significance when viewed in relation to a concept the importance of which has already been stressed in relation to the MM, namely personal experience: this is the only legitimate criterion to verify our knowledge (Mansfeld 1981). Therefore it seems that also in this case by highlighting the limits of human experience, Protagoras was engaging in a polemic with those Presocratic thinkers, such as Parmenides and Heraclitus, who had repeatedly claimed to be able to transcend the limits of human knowledge, as well as the poets, who had based their authority on a privileged contact with the divine world. In this respect, some interesting similarities are to be found between Protagoras and Xenophanes of Elea (21B34 DK), who also reportedly criticised human claims to know the truth about the gods (significantly, for Xenophanes too, obscurity is an obstacle to knowledge). The analogies with Xenophanes become even more striking when we consider the second segment of the first statement, concerning the presumed appearance of the gods. In raising this problem, Protagoras was in all likelihood referring to the anthropomorphic conception, which Xenophanes had already repeatedly censured (see also Herodotus Histories II 53,1; Sassi 2013).