Page:Mind (New Series) Volume 9.djvu/483

III.-THE PRINCIPLE OF LEAST ACTION AS A PSYCHOLOGICAL PRINCIPLE. BY W. E. BOYCE GIBSON. I. THE PHYSICAL PRINCIPLE OF LEAST ACTION. THE principle of Least Action is no doubt best known as a leading generalisation of Mechanical Science. As such it can of course have no obvious connexion with any psycho- logical principle. A principle, to have psychological value, must be a principle for the explanation of psychical facts, and not a principle imported from another science on the ground that it has proved effective in explaining the facts of that science. The tendency to extend the explanatory office of a principle or category beyond the realm of facts for which it was originally designed is however so strong that one almost feels called upon to justify one's self for not indulging in so prevalent a weakness. This I propose to do at the outset 03" a short critical estimate of the meaning of the Principle of Least Action in Mechanical Science. I consider it has been the misfortune of Mechanical Science that its principles should not have been given names having associations of a strictly mechanical kind. It has sometimes seemed to me as though the illusions produced by the psychical associations of the name were to a certain extent responsible for the subsequent appropriation of these mechanical principles by Philosophy for the elucidation of mental phenomena. A law which explains a number of material phenomena is given a name suggesting some psychical activity ; it is called a law of Inertia, of Attraction, of Least Constraint, of Eepose, of Least Action ; and then Philosophy, brooding over the name without an expert knowledge of the facts designated by the name, has sight of some profound cosniological principle and does not see why what has cosmological significance should not apply to movements of mind as well as to the movements of matter; are not the phenomena of mind expressive also of inertia, of a dislike to constraint, of a preference for least action ? It