Upon the revival of the study of law and jurisprudence in the 11th and 12th centuries several of the more famous jurists of that time, Azo, Irnerius, Placentinus and others, essayed definitions of justice, but they do not seem to have improved upon Ulpian. Their definitions were vitiated by theological assumptions and none of them has become a text for commentators or students. Neither in modern times has any definition of justice been suggested which has received such universal assent as did that of Ulpian in his time and for centuries afterward. We may therefore return to Ulpian's definition as our point of departure, since his definition is substantially that suggested earlier by Aristotle, and observations on the later will also apply in many respects to the earlier. Ulpian's definition is elegant in style, but it does not carry us very far in our inquiry. We are told indeed that justice is a state or disposition of the mind, the disposition to render to everyone his right or, as put by Aristotle, is the disposition to distribute according to desert. It was this statement that captured the medieval jurists and which they made their text, but it is now regarded as incomplete and even inaccurate. One may have the disposition, the desire, the will, to render to every one his right, but unless he can know what is his fellow's right he may unwittingly fail to accord it to him and thus unwittingly do injustice. It evidently is not enough to have the disposition or will; hence the definition is incomplete, and any definition is incomplete which does not furnish a criterion for determining what is the given man's right. But the definition as far as it does go is not strictly accurate. The man of malevolent disposition who would wrong his fellow if he dared, may yet, to avoid unpleasant consequences to himself, render fully to every other man his right. It would seem, therefore, that justice is an attribute or quality of conduct rather than a disposition or state of mind, and of conduct toward others rather than of conduct toward one's self. It is only of the conduct of men in their relations to other men that we can predicate justice or injustice. One's conduct may result in good or evil to himself and so be wise or unwise, but assuming, what probably is never the fact, that it affects only himself, in no way affects any other, his conduct is neither just nor unjust. Robinson Crusoe, until the arrival of the man Friday, had no occasion to consider our problem.