will, in philosophy and psychology, term used to describe that which is alleged to stimulate the motivation of purposeful activity. It is characteristic of the will that it can be observed only in oneself and can be attributed to others only by inference from their behavior. There is no generally accepted explanation in psychology for the apparent freedom people enjoy to do what they will, i.e., to originate the stimuli necessary to initiate a course of action. Until recently the psychological discussions of the will have been closely related to the philosophical. Disagreements have been extreme. One approach has been the doctrine of determinism, which denies the reality of the will. Another type simply accepts the will—the motive power of the personality—as the faculty or function of the person. This idea is generally based on intuitive grounds and is associated with Plato, Aristotle, Lucretius, St. Thomas Aquinas, René Descartes, and Immanuel Kant. Others have considered it the externalized result of the interaction of conflicting elements. These include Baruch Spinoza, G. W. von Leibniz, David Hume, J. G. Herbart, Wilhelm Wundt, Herbert Spencer, and Hugo Münsterberg. Still others have considered the will to be the manifestation of the personality striving to accomplish its purposes. Among these are St. Augustine, Duns Scotus, Thomas Hobbes, Arthur Schopenhauer, Friedrich Nietzsche, William McDougall, and John Dewey. Modern psychology has tended to consider the concept of the will as an unscientific principle. The problems involved in dealing with it are largely absorbed in other areas of investigation, such as the psychology of adjustment, the study of unconscious motivation, the concept of attention, and the influence of endocrine balance.