The special forms that the one great virtue of seeking the relative mean takes in actual life bear a close correspondence to the cardinal virtues of Plato; yet with a difference which marks a positive advance in insight. Aristotle, to begin with, distinguishes wisdom from prudence. Wisdom is the theoretic knowledge of things as they are, irrespective of their serviceableness to our practical interests. In modern terms it is devotion to pure science. This corresponds to Plato's contemplation of the Good. According to Aristotle this devotion to knowledge for its own sake underlies all virtue; for only he who knows how things stand related to each other in the actual world, will be able to grasp aright that relation of means to ends on which the success of the practical life depends. Just as the engineer cannot build a bridge across the Mississippi unless he knows those laws of pure mathematics and physics which underlie the stability of all structures, so the man who is ignorant of economics, politics, sociology, psychology, and ethics is sure to make a botch of any attempts he may make to build bridges across the gulf which separates one man from another man; one group of citizens from another group. Pure science is at the basis of all art, consciously or unconsciously; and therefore wisdom is the fundamental form of virtue. Prudence comes next; the power to see, not the theoretical relations of men and things to each other, but the practical relationships of men and things to our self-chosen ends. Wisdom knows the laws which govern the strength of materials. Prudence knows how strong a structure is necessary to support the particular strain we wish to place upon it. Wisdom knows sociology. Prudence tells us whether in a given case it is better to give a beggar a quarter of a dollar, an order on a central bureau, a scolding, or a kick. The most essential, and yet the rarest kind of prudence is that considerateness which sensitively appreciates the point of view of the people with whom we deal, and takes proper account of those subtle and complex sentiments, prejudices, traditions, and ways of thinking, which taken together constitute the social situation.