Other cases are recorded which show that anti-religious thought was liable to be persecuted.  Protagoras, one of the greatest of the Sophists, published a book On the Gods, the object of which seems to have been to prove that one cannot know the gods by reason.  The first words ran:  “Concerning the gods, I cannot say that they exist nor yet that they do not exist.  There are more reasons than one why we cannot know.  There is the obscurity of the subject and there is the brevity of human life.”  A charge of blasphemy was lodged against him and he fled from Athens.  But there was no systematic policy of suppressing free thought.  Copies of the work of Protagoras were collected and

[29] burned, but the book of Anaxagoras setting forth the views for which he had been condemned was for sale on the Athenian book-stalls at a popular price.  Rationalistic ideas moreover were venturing to appear on the stage, though the dramatic performances, at the feasts of the god Dionysus, were religious solemnities.  The poet Euripides was saturated with modern speculation, and, while different opinions may be held as to the tendencies of some of his tragedies, he often allows his characters to express highly unorthodox views.  He was prosecuted for impiety by a popular politician.  We may suspect that during the last thirty years of the fifth century unorthodoxy spread considerably among the educated classes.  There was a large enough section of influential rationalists to render impossible any organized repression of liberty, and the chief evil of the blasphemy law was that it could be used for personal or party reasons.  Some of the prosecutions, about which we know, were certainly due to such motives, others may have been prompted by genuine bigotry and by the fear lest sceptical thought should extend beyond the highly educated and leisured class.  It was a generally accepted principle among the Greeks, and afterwards among the Romans, that religion was a good and necessary thing

[30] for the common people.  Men who did not believe in its truth believed in its usefulness as a political institution, and as a rule philosophers did not seek to diffuse disturbing “truth” among the masses.  It was the custom, much more than at the present day, for those who did not believe in the established cults to conform to them externally.  Popular higher education was not an article in the programme of Greek statesmen or thinkers.  And perhaps it may be argued that in the circumstances of the ancient world it would have been hardly practicable.

There was, however, one illustrious Athenian, who thought differently—­Socrates, the philosopher.  Socrates was the greatest of the educationalists, but unlike the others he taught gratuitously, though he was a poor man.  His teaching always took the form of discussion; the discussion often ended in no positive result, but had the effect of showing that some received opinion was untenable and that truth is difficult to ascertain.  He had indeed certain definite views about knowledge and virtue, which are of the highest importance in the history of philosophy, but for our present purpose his significance lies in his enthusiasm for discussion and criticism.  He taught those with whom he conversed—­and he conversed indiscriminately