All relationships of people to each other rest, as a matter of course, upon the precondition that they know something about each other. The merchant knows that his correspondent wants to buy at the lowest price and to sell at the highest price. The teacher knows that he may credit to the pupil a certain quality and quantity of information. Within each social stratum the individual knows approximately what measure of culture he has to presuppose in each other individual. In all relationships of a personally differentiated sort there develop, as we may affirm with obvious reservations, intensity and shading in the degree in which each unit reveals himself to the other through word and deed. How much error and sheer prejudice may lurk in all this knowing is immaterial. Just as our apprehension of external nature, along with its elusions and its inaccuracies, still attains that degree of truth which is essential for the life and progress of our species, so each knows the other with whom he has to do, in a rough and ready way, to the degree necessary in order that the needed kinds of intercourse may proceed. That we shall know with whom we have to do, is the first precondition of having anything to do with another. The customary reciprocal presentation, in the case of any somewhat protracted conversation, or in the case of contact upon the same social plane, although at first sight an empty form, is an excellent symbol of that reciprocal apprehension which is the presumption of every social relationship...