Bentham's positive assertion that, "what happiness is every man knows, because, what pleasure is, every man knows," is met by counter-assertions equally positive. "Who can tell," asks Plato, "what pleasure really is, or know it in its essence, except the philosopher, who alone is conversant with realities."[D] Aristotle, too, after commenting on the different opinions held by the vulgar, by the political, by the contemplative, says of happiness that, "to some it seems to be virtue, to others prudence, and to others a kind of wisdom: to some again, these, or some one of these, with pleasure, or at least, not without pleasure; others again include external prosperity."[E] And Aristotle, like Plato, comes to the remarkable conclusion that the pleasures of the intellect, reached by the contemplative life, constitute the highest happiness![F] How disagreements concerning the nature of happiness and the relative values of pleasures, thus exhibited in ancient times, continue down to modern times, is shown in Mr. Sidgwick's discussion of egoistic hedonism, above commented upon. Further, as was pointed out before, the indefiniteness attending the estimations of pleasures and pains, which stands in the way of egoistic hedonism as ordinarily conceived, is immensely increased on passing to universalistic hedonism as ordinarily conceived; since its theory implies that the imagined pleasures and pains of others are to be estimated by the help of these pleasures and pains of self already so difficult to estimate. And that any one after observing the various pursuits into which some eagerly enter, but which others shun, and after listening to the different opinions concerning the likeableness of this or that occupation or amusement, expressed at every table, should assert that the nature of happiness can be fully agreed upon, so as to render it a fit end for direct legislative action, is surprising. The accompanying proposition that justice is unintelligible as an end is no less surprising. Though primitive men have no words for either happiness or justice, yet even among them an approach to the conception of justice is traceable. The law of retaliation, requiring that a death inflicted by one tribe on another, shall be balanced by the death either of the murderer or some member of his tribe, shows us in a vague shape that notion of equalness of treatment which forms an essential element in it.