Hartley's was the earliest systematic attempt to explain the whole development of experience by the Association of Ideas. He accounted for the more complex feelings-even such feelings as "the moral_sense and "theopathy"-as developments of simpler mental conditions; and association was the principle by which he explained their origin. Since his day the “association" theory has been developed so far beyond the point to which he brought it that his early attempt is now apt to be forgotten. But Hartley's work is significant not only on account of his conclusions, important as these are, but also because his is practically the earliest attempt to furnish a complete analysis of mental function. Encumbered as it is with ethical and theological reflections, his philosophy is primarily an inductive study of human consciousness, designed to show what its elements are, and by what process they are combined; and his problem itself is hardly less significant, in relation to Mill's view of moral science, than the solution which he offers. The theory of mental association, as Hartley explains it, is not only a statement of the mode in which states of consciousness succeed one another; it contains also a fairly definite account of the process by which the mental complex acquires the character which it exhibits in our experi ence. The doctrine that our more complex ideas reflect the mode in which our simpler experiences have actually been combined in the past represents the content of consciousness as the product of circumstances: it implies a complete subordination of mental develop ment to the order of external events; and such a conception of the way in which our mental dispositions arise makes them the direct continuation of the environment in which we have grown up. To say that we may expect to find these same relations in the mental or internal process which we have observed in the outer world of spatial existence is merely to state this view of mental life in a slightly altered form of words; and it is therefore worthy of note that, although Mill does not always appear to be quite satisfied with the account which the Association Psychology gives of mental functions, he never doubts the complete dependence of these functions upon the course of external events, or the possibility which that dependence confirms of studying conduct by the methods proper to natural sciences.2 But, in relation to the method of moral science, even the extent of Hartley's use of the principle of mental association is less important than the interpretation of that principle which is offered by his physiological conception of it. The basis of Hartley's system of psychology and ethics is a revised idea of nervous action. The earlier physiology had followed without question the lead of those physicists who explained light and heat and magnetism as imponderable fluids; and it had conceived the function of nerves to be the transmission of such a fluid. Hartley, on the other hand, accounts for nervous action by a doctrine "taken from the hints concerning the 2 Pp. 18 note 1, 45 note 1. 1 P. 45. performance of sensation and motion, which Sir Isaac Newton has given at the end of his Principia, and in the questions annexed to his Optics."1 We need not here examine in detail an hypothesis which, so far as its physiology of nervous action is concerned, has long been obsolete; but it is worth remarking that Hartley's starting-point is a physiological adaptation of Newton's doctrine of ethereal vibrations. Hartley affirms that "external objects impressed upon the Senses occasion, first in the Nerves on which they are impressed, and then in the Brain, vibrations of the small and, as one may say, infinitesimal medullary particles; "2 and he supposes that, when these vibrations are repeated, they tend to produce "a Disposition to diminutive Vibrations," or "Vibratiuncles," which correspond to them, or are their " Miniatures." It is by the connection which frequent concurrence of definite vibrations establishes between their miniatures that the association of the ideas or movements corresponding to these miniatures is determined. This idea, that mental association corresponds to nervous habit, is of considerable interest in relation to the method of mental and moral science. Hartley, it must be observed, although his whole theory turns on the answer to the question how vibration" and association” are related, has nothing more convincing to say than that "the doctrine of vibrations may appear at first sight to have no connection with that of associa 1 Observations on Man, Part I. chap. i. 3 Ib., Prop. VIII. C 1 tion; however, if these doctrines be found in fact to contain the laws of the bodily and mental powers respectively, they must be related to each other, since the body and mind are. One may expect that vibrations should infer association as their effect, and association point to vibrations as its cause." But, however little Hartley may justify or even define his assumption of a correspondence or a causal relation between mental and organic events, his suggestion of a psycho-physical theory connects itself with the question how far inductive method, as Mill conceives it, can be applied to conduct. Physical events are the only phenomena in which we can hope to discover a complete continuity: they alone consist of changes which form a causal series. Consciousness is essentially discontinuous; for not only is its course perpetually interrupted, so that intervals of time elapse between its states; but, even when there is no break of this sort, the mental process does not exhibit the orderly progress which is found in physical phenomena. We see that mental conditions generally succeed one another in a certain way; but between stages of the mental process, as we know it, there is never any self-evident connection. Now, the causal connection for which we look in vain between the stages of our mental life is sought there because it is suggested by the kind of knowledge which we have of physical facts; for it is in our experience of physical changes that we discover the unconditional relation which is the only ground, according to Mill, for the 1 Observations on Man, Part I. chap. i. application of inductive method. It is thus of no small. importance for our knowledge of mental and moral subjects if we can connect them with that physical order which reveals causal connections, and which can be made the object of induction and scientific knowledge. It must be remembered that Mill himself adopts a critical attitude towards the use of physiological principles in the explanation of mental states. He is both too well aware of the difficulties of the method and too little intent upon system at any price to accept Hartley's artificially simple solution; and he argues, against Comte's similar reduction of psychology to physiology, that introspection is the essential method of our knowledge of mind, and that only the direct knowledge of mental facts which introspection gives can impart psychological meaning to physiological data.1 On the other hand, Mill actually adopts a physiological explanation when the incompleteness of purely psychological analysis is really brought home to him— as in the case of those phenomena which Hamilton and others had explained by the hypothesis of "unconscious mental" modifications; and he sometimes affirms the dependence of all exact psychology upon physiology.2 Even when he does not do this, he seems to entertain a view of the functions of psychology which applies rather to such a physiological development of it as Hartley had suggested than to the mere description of mental states and changes. A psychology fitted to be the basis of ethology and of social science, and to dis1 Pp. 36 ff., 39 note 1. P. 39 note 1. |