9. _Political_ economy, as the term implies, has reference to man in society,—to “the body politic.” The social element in man is as imperative as any part of his constitution. Man’s greatest need is _association_. The solitary individual is only a minute constituent of man in man’s relation to the main purposes of life. No man is complete in himself. He must be supplemented by others, generally by many others, and he must find a large part of his own completeness in this association. Each has something that others lack, and we are designed to be sources of mutual supply to our several wants. Here emerges another vital fact. _Individuality_ is as indispensable as association. A superficial thinker might regard these characteristics as antagonistic. The fact is so far otherwise that each is really dependent on the other. Men must _differ_ in order to be of any use to one another. It is the difference that makes the individuality. Mutual aid is the object of association. Hence the greater the difference, the greater the individuality; and the greater the individuality, the greater the association. No man would associate with another unless the one had something which the other lacked. But for this there would be no commerce. Two farmers producing nothing but wheat would have nothing to exchange with each other. Two men of precisely the same mental possessions, habits and aptitudes, would never be companions for each other. On the other hand it is only by association that individuality becomes the most highly developed. Only by such development do the differences among men become great and numerous. In the lower grades of humanity there is comparatively little difference between individuals, and there is little association. It is only in advanced civilization that a strongly marked individuality exists, and that we find those numerous differences which make the mutual dependence the greatest. Here is a potent reason for the study of this subject. It is impossible to estimate the power of association in production alone. It is known in a general way that the combination of men gives greatly increased results as compared with those of men working separately. Yet it is not nearly realized that a hundred men properly associated in an industrial enterprise will often effect two or three hundred times as much as all the very same men working separately.