Such scepticism appears in general to be based upon the idea that a practical psychology in the sense already defined is impossible. According to some this is because the human will introduces into conduct an element necessarily incommensurable, which will always render the behaviour of man subject to the occurrence of true variety and therefore beyond the reach of scientific generalization; according to another and a more deterministic school, human conduct, while not theoretically liable to true variety in the philosophic sense or to the intrusion of the will as a first cause, is in fact so complex that no reduction of it to a complete system of generalizations will be possible until science in general has made very great progress beyond its present position. Both views lead in practice to attitudes of equal pessimism towards sociology. The observable complexity of human conduct is, undoubtedly, very great and discouraging. The problem of generalizing from it presents, however, one important peculiarity, which is not very evident at first sight. It is that as observers we are constantly pursued by man’s own account of his behaviour; that of a given act our observation is always more or less mixed with a knowledge, derived from our own feelings, of how it seems to the author of the act, and it is much more difficult than is often supposed to disentangle and allow for the influence of this factor. Each of us has the strongest conviction that his conduct and beliefs are fundamentally individual and reasonable and in essence independent of external causation, and each is ready to furnish a series of explanations of his conduct consistent with these principles. These explanations, moreover, are the ones which will occur spontaneously to the observer watching the conduct of his fellows.