236 THE AMERICAN JOURNAL OF SOCIOLOGY
it necessary to assume the existence of underlying interests. These have to desires very nearly the relation of substance to attribute, or, in a different figure, of genus to species. Our interests may be beyond or beneath our ken ; our desires are strong and clear. I may not be conscious of my health interests in any deep sense, but the desires that my appetites assert are specific and concrete and real. The implicit interests, of which we may be very imperfectly aware, move us to desires which may correspond well or ill with the real content of the interests. At all events, it is these desires which make up the active social forces, whether they are more or less harmonious with the interests from which they spring. The desires that the persons associating actually feel are practically the elemental forces with which we have to reckon. They are just as real as the properties of matter. They have their ratios of energy, just as certainly as though they were physical forces. They have their peculiar modes of action, which may be formulated as dis- tinctly as the various modes of chemical action.
The only scientific doubt which is admissible about the social forces concerns the division of labor in studying them. If the social forces are human desires, is not the study of them psy- chology, rather than sociology? We may answer both "yes" and " no." In the sense that both psychology and sociology either begin or end in each other, the study of the social forces belongs to psychology. In the sense that either psychology or sociology can be supposed to treat a whole situation, if its dis- tinctive point of view is held apart from the other point of view, neither psychology nor sociology can be credited with sole responsibility for interpretation of the social forces. The empha- sis of psychology is upon discrimination of the mental activities (in this case the desires) and the mechanism of their action. The emphasis of sociology is upon the social stimuli of the desires, upon the various content which they carry in different situations, and upon their operation within associations of per- sons. The relations of psychology and sociology to knowledge of the social forces are consequently complementary, not com- petitive.
