DAVID HARTLEY, (1705-1757), who may justly be called the founder of the English Association school of psychologists, was born on the 30th August 1705. His father, who was vicar of Armley in Yorkshire, wished him to enter the church ; and with this view he was sent at the age of fifteen to Jesus College, Cambridge, where he studied under Saunderson the mathematician, and distinguished himself so much that he was elected a fellow of his college. But his university career so far modified his opinions that, feeling himself no longer able conscientiously to sign the Thirty-nine Articles, he abandoned his first intention and devoted himself to the study of medicine. He, however, remained in the communion of the English Church, living on intimate terms with the most distinguished churchmen of his day, among whom may be named Joseph Butler, Warburton, Law, Hoadley, and the poet Young. Indeed he asserted it to be a duty to obey esclesiastical as well as civil authorities. The doctrine to which he most strongly objected was that of eternal punishment. His keen interest in theology is proved by the fact that he devoted a large part of his Observations to that subject, the objective side of which he treated upon orthodox lines. The life of Hartley was the useful life of a benevolent and studious physician. He practised at Newark, Bury St Edmunds, London, and lastly at Bath, where he died on the 28th August 1757, within two days of his fifty-second birthday. It was at the age of twenty-five that he commenced the series of essays that was to make up his Observations on Man : his Frame, his Duty, and his Expectations. The praise of originality cannot be denied him. It is noteworthy, however, that very nearly at the same time with the publication of Hartley's Observations (1749), two works appeared in French expounding theories essentially similar to hisCondillac's Traite sur VOrigine des Connoissances humaines (1746) and the Traite Analytique de I'Ame by Charles Bonnet of Geneva, whose coincidence with Hartley in the most distinctive features of his philosophy is ex-tremely remarkable. But Hartley's own account of the matter is so straightforward as to command immediate assent. His physical theory, he tells us, was drawn from certain speculations as to nervous action which Newton had published in his Principia. His psychological theory was suggested by an Essay on the Fundamental Principle of Virtue or Morality (written by a clergyman named Gay, and prefixed by Law to his translation of Archbishop King's Latin work on the Origin of Evil), the chief object of which was to show that sympathy and conscience are developments by means of association from the selfish feelings. It is greatly to Hartley's credit that he so frankly owned his obligations to a work so far inferior to his own in completeness and tone of thought.
The outlines of Hartley's theory are as follows. With Locke he asserted that, prior to sensation, the human mind is a blank. By a growth from simple sensations those states of consciousness which appear most remote from sensation come into being. And the one law of growth of which Hartley took account was the law of contiguity, synchronous and successive. By this law he sought to explain, not only the phenomena of memory, which others had similarly explained before him, but also the phenomena of emotion, of reasoning, and of voluntary and involuntary action.
By his physical theory Hartley gave the first strong impulse to the modern study of the intimate connexion of physiological and psychical facts which has proved so fruitful, though his physical theory in itself is inadequate, and has not been largely adopted. He held that sensation is the result of a vibration of the minute particles of the medullary substance of the nerves, to account for which he postulated, with Newton, a subtle elastic ether, rare in the interstices of solid bodies and in their close neighbourhood, and denser as it recedes from them. Pleasure is the result of moderate vibrations, pain of vibrations so violent as to break the continuity of the nerves. These vibrations leave behind them in the brain a tendency to fainter vibrations or " vibratiuncles" of a similar kind, which correspond to "ideas of sensation." Thus memory is accounted for. The course of reminiscence and of the thoughts gene-rally, when not immediately dependent upon external sensation, is accounted for on the ground that there are always vibrations in the brain on account of its heat and the pulsation of its arteries. What these vibrations shall be is determined by the nature of each man's past experience, and by the influence of the circumstances of the moment, which causes now one now another tendency to pre-vail over the rest. Sensations which are often associated together become each associated with the ideas corresponding to the others: and the ideas corresponding to the associated sensations become associated together, sometimes so intimately that they form what appears to be a new simple idea, not without careful analysis resolvable into its component parts.
Starting, like the modern Associationists, from a detailed account of the phenomena of the senses, Hartley tries to show how, by the above laws, all the emotions, which he analyses with considerable skill, may be explained. Locke's incomplete phrase "association of ideas " is employed throughout, " idea " being taken as includ-ing every mental state but sensation. He emphatically asserts the existence of pure disinterested sentiment, while declaring it to be a growth from the self-regarding feelings. Voluntary action is explained as the result of a firm connexion between a motion and a sensation or "idea," and, on the physical side, between an '' ideal " and a motory vibration. Therefore in the Freewill controversy Hartley took his place as a Determinist. It is singular that, as he tells us, it was only with reluctance, and when his speculations were nearly complete, that he came to a conclusion on this subject in accordance with his theory.
Hartley's theory of reasoning is forced into agreement with the rest of his system. He declares that "assent and dissent, what-ever their precise and particular nature may be, must come under the notion of ideas, being only those very complex internal feelings which adhere by association to such clusters of words as are called propositions .... And thus a mathematical proposition is nothing more than a group of ideas united by association," this group of ideas including '' not only the sum of the ideas belonging to the terms of the proposition, but also those which belong to equality, coincidence, and truth."
The remaining half of the Observations is devoted to discussion of theological questions and to practical ethics, and does not call for detailed notice. While emphatically asserting his faith in supernatural religion, in the psychological part of his work he treats, not only conscience, but also the religious emotions entirely as developments from sensation, in the same sense as the pleasures of imagination.
Clearness, freedom from redundancy, and a severe simplicity and brevity are the best characteristics of his style. "No book," writes Sir James Mackintosh, " perhaps exists which, with so few of the common allurements, comes at last so much to please by the picture it presents of the writer's character .... Whoever bestows a careful perusal on the work must be unfortunate if he does not see, feel, aud own that the writer was a great philosopher and a good man." (T. M. W.)