Because Psychology studies mental processes, it is very liable to behave as if Logic…were one of its subdivisions. But in fact Psychology, like every other science, must presuppose the autonomy of Logic; otherwise the writings of psychologists could be no more than their own autobiographies–not nearly so interesting or important as the autobiographies of statesmen, soldiers or artists. The interest which a psychologist claims for his theory is not that he happens to hold it, but that it is a true account of your experience and mine as well as of his own. But in this case he must have something to say in support of his theory over and above its psychological history. For every theory ever held has a psychological history.