As to Protagoras of Abdera, one of the earliest and most famous of all the sophists, it is stated that he began a pamphlet treating of the gods with the words: “Concerning the gods I can say nothing, neither that they exist nor that they do not exist, nor of what form they are; because there are many things which prevent one from knowing that, namely, both the uncertainty of the matter and the shortness of man’s life.” On this account, it is said, he was charged with impiety at Athens and was outlawed, and his works were publicly burned. The date of this trial is not known for certain; but it is reasonably supposed to have coincided with that of Diagoras, namely, in 415. At any rate it must have taken place after 423-421, as we know that Protagoras was at that time staying in Athens. As he must have been born about 485, the charge overtook him when old and famous; according to one account, his work on the gods seems to belong to his earlier writings.
To doubt the correctness of this tradition would require stronger reasons than we possess, although it is rather strange that the condemnation of Protagoras is mentioned neither in our historical sources nor in Aristophanes, and that Plato, who mentions Protagoras rather frequently as dead, never alludes to it. At any rate, the quotation from the work on the gods is certainly authentic, for Plato himself referred to it. Hence it is certain that Protagoras directly stated the problem as to the existence of the gods and regarded it as an open question. But beyond that nothing much can be deduced from the short quotation; and as to the rest of the book on the gods we know nothing. The meagre reasons for scepticism adduced probably do not imply any more than that the difficulties are objective as well as subjective. If, in the latter respect, the brevity of life is specially mentioned it may be supposed that Protagoras had in mind a definite proof of the existence of the gods which was rendered difficult by the fact that life is so brief; prediction of the future may be guessed at, but nothing certain can be stated.
Protagoras is the only one of the sophists of whom tradition says that he was the object of persecution owing to his religious views. The trial of Socrates, however, really belongs to the same category when looked at from the accusers’ point of view; Socrates was accused as a sophist. But as his own attitude towards popular religion differed essentially from that of the sophists, we cannot consider him in this connexion. Protagoras’s trial itself is partly determined by special circumstances. In all probability it took place at a moment when a violent religious reaction had set in at Athens owing to some grave offences against the public worship and sanctuaries of the State (violation of the Mysteries and mutilation of the Hermae). The work on the gods had presumably been in existence and known long before this without causing scandal to anybody. But, nevertheless, the trial, like those of Anaxagoras and Socrates, plainly bears witness to the animosity with which the modern free-thought was regarded in Athens. This animosity did not easily manifest itself publicly without special reasons; but it was always there and might always be used in case of provocation.