Man is the measure of all things, of things that are that they are, and of things that are not that they are not.
ProtagorasEveryone, including the Athenians [...] are right to accept advice from anyone, since it is incumbent on everyone to share in that sort of excellence, or else there can be no city at all.
ProtagorasAbout the gods I have no means of knowing either that they exist or that they do not exist or what they are to look at. Many things prevent my knowing. Among others, the fact that they are never seen.
ProtagorasMany things prevent knowledge, including the obscurity of the subject and the brevity of human life
Protagoras