Anaxagoras’ great service, then, was his introduction of Mind into philosophy as a formative, a motive principle to provide the cause for change and diversity. It is not to be denied that Anaxagoras conceived his principle to be as material as the elements themselves, and that he did not employ his principle fully, even after he introduced it into the world. Indeed, he did not advance beyond a mechanical concept of the cause of phenomena. But nevertheless he is significant in the history of European thought as the founder of the dualistic system which largely prevailed thereafter. His contemporaries, too, recognized him as an innovator, for we are told that the wits of Athens nicknamed him “Mind.” With the consequences of this new dualism we shall be much concerned hereafter. Another group of men contributed to the intellectual life of that wonderful fifty years of Athenian history which began with the defeat of the Persians and ended with the outbreak of the Peloponnesian War. How keen the intellectual life of that time was is shown by the high excellence of the plays to which the masses of the common citizens listened in the theater. Aeschylus, Sophocles, and Euripides were not enjoyed by the few but by the great body of Athenian citizens, and their plays were known even among the remote Greek colonies. The intellectual spirit of the age was stimulated to inquiry and to scepticism. Herodotus is wholly sceptical, and the agnostic tendency of the time is shown by the entire lack of mythology and superstition displayed by Thucydides. A further stimulus was furnished by the development of a higher education given by professional teachers—the Sophists.