We have now reached the great point on which the Stoic ethics differed from that of Plato and Aristotle. The two latter, while upholding virtue as the highest good, allowed external advantages like pleasure and exemption from pain to enter into their definition of perfect happiness; nor did they demand the entire suppression of passion, but, on the contrary, assigned it to a certain part in the formation of character. We must add, although it was not a point insisted on by the ancient critics, that they did not bring out the socially beneficent character of virtue with anything like the distinctness of their successors. The Stoics, on the other hand, refused to admit that there was any good but a virtuous will, or that any useful purpose could be served by irrational feeling. If the passions agree with virtue they are superfluous, if they are opposed to it they are mischievous; and once we give them the rein they are more likely to disagree with than to obey it.[52] The severer school had more reason on their side than is commonly admitted. Either there is no such thing as duty at all, or duty must be paramount over every other motive—that is to say, a perfect man will discharge his obligations at the sacrifice of every personal advantage. There is no pleasure that he will not renounce, no pain that he will not endure, rather than leave them unfulfilled. But to assume this supremacy over his will, duty must be incommensurable with any other motive; if it is a good at all, it must be the only good. To identify virtue with happiness seems to us absurd, because we are accustomed to associate it exclusively with those dispositions which are the cause of happiness in others, or altruism; and happiness itself with pleasure or the absence of pain, which are states of feeling necessarily conceived as egoistic. But neither the Stoics nor any other ancient moralists recognised such a distinction. All agreed that public and private interest must somehow be identified; the only question being, should one be merged in the other, and if so, which? or should there be an illogical compromise between the two. The alternative chosen by Zeno was incomparably nobler than the method of Epicurus, while it was more consistent than the methods of Plato and Aristotle. He regarded right conduct exclusively in the light of those universal interests with which alone it is properly concerned; and if he appealed to the motives supplied by personal happiness, this was a confusion of phraseology rather than of thought.