do ten years hence, or what another should do at this time. It may indeed happen to decide ten years hence as it does now, and to decide a second case now as it now decides a first; still its present act is for the present, not for the distant or the future. State or public law is inflexible, but this mental rule is not only minute and particular, but has an elasticity, which, in its application to individual cases, is, as I have said, not studious to maintain the appearance of consistency. In old times the mason’s rule which was in use at Lesbos was, according to Aristotle, not of wood or iron, but of lead, so as to allow of its adjustment to the uneven surface of the stones brought together for the work. By such the philosopher illustrates the nature of equity in contrast with law, and such is that _phronesis_, from which the science of morals forms its rules, and receives its complement. In this respect of course the law of truth differs from the law of duty, that duties change, but truths never; but, though truth is ever one and the same, and the assent of certitude is immutable, still the reasonings which carry us on to truth and certitude are many and distinct, and vary with the inquirer; and it is not with assent, but with the controlling principle in inferences that I am comparing _phronesis_. It is with this drift that I observe that the rule of conduct for one man is not always the rule for another, though the rule is always one and the same in the abstract, and in its principle and scope. To learn his own duty in his own case, each individual must have recourse to his own rule; and if his rule is not sufficiently developed in his intellect for his need, then he goes to some other living, present authority, to supply it for him, not to the dead letter of a treatise or a code. A living, present authority, himself or another, is his immediate guide in matters of a personal, social, or political character. In buying and selling, in contracts, in his treatment of others, in giving and receiving, in thinking, speaking, doing, and working, in toil, in danger, in his recreations and pleasures, every one of his acts, to be praiseworthy, must be in accordance with this practical sense. Thus it is, and not by science, that he perfects the virtues of justice, self-command, magnanimity, generosity, gentleness, and all others. _Phronesis_ is the regulating principle of every one of them.