Apart from physical science, we learn that Anaxagoras was a close friend and adviser of the great Athenian statesman, Pericles; and we have by chance an account of a long discussion between the two men about the theory of punishment--whether the object of it is to do "justice" upon a wrong-doer apart from any result that may accrue, or simply to deter others from doing the same and thus make society better. The question is the subject of a vigorous correspondence in the _Times_ while these words are writing. We can understand what an effect such a teacher as this would have on the eager young man from Phlya. One great word of liberation was already in the air and belongs to no one sophist or philosopher. This was the distinction between Nature on the one hand and Custom or Convention on the other. The historian Herodotus, who was no sophist but loved a good story, tells how the Persian king, Darius, called some Greeks and some Indian tribesmen together into his presence. He then asked the Greeks what payment would induce them to eat the dead bodies of their fathers. "Nothing in the world," they cried in indignation. "They would reverently burn them." He proceeded to ask the Indians what they would take to burn their fathers' bodies, and they repelled the bare thought with horror; they would do nothing but eat them with every mark of love and respect. "Fire burns in the same way both here and in Persia," the saying was, "but men's notions of right and wrong are not at all the same." The one is Nature; the other is man's Custom or Convention. This antithesis between "Phusis" and "Nomos" ran vividly through the whole of Greek philosophy, and awoke with renewed vigour in Rousseau and the radical writers of the eighteenth century. It is an antithesis against which conformist dialecticians have always turned their sharpest weapons. It has again and again been dissected and refuted and shown to be philosophically untenable: but it still lives and has still something of the old power to shatter and to set free. All the thinkers of Greece at the time we are treating were testing the laws and maxims of their day, and trying to find out what really rested on Nature and what was the mere embroidery of man. It is always a dangerous and exciting inquiry; especially because the most irrational conventions are apt also to be the most sacrosanct.