David Hartley was once a controversial and influential thinker. His 1749 magnum opus Observations on Man, His Frame, His Duty, and His Expectations delves into "neurology, moral psychology, and spirituality" (Allen). Intellectual notables such as Joseph Priestly and Samuel Taylor Coleridge valued his work highly. In later years, however, his work suffered from increasing criticism and eventually fell into disregard.

Hartley grounded the mind in the brain in an era when mind-body dualism was still popular. In his "psycho-physiological" system, which Newton's physical theories inspire, "sensation causes vibration" (Huguelet, ix) in the nerves. This vibration passes instantly to the brain, where it enters into consciousness and leaves a miniature trace of itself, called a vibratiuncle. Hartley argues that "if we allow that original impressed vibratory motions leave a tendency to miniature ones of the same kind . . . it will follow that sensations must beget ideas" (Hartley, 64). By "idea" Hartley means any non-sensory mental phenomenon. Simple ideas build associations with one another and turn into more complex ideas. The brain constantly vibrates with these ideas, which constitute consciousness.

Hartley was a religious as well as scientific thinker. He "affirms universal salvation" (Allen), the notion that everyone will be re-united with God. Science and religion did not conflict in the eighteenth century like they often do today, and indeed Hartley works his faith into his science. "The psychological dynamic of association" (Allen), he argues, has a natural tendency to bring people to salvation. The second volume of Observations , which focuses on the moral and spiritual implication of his findings, is the larger of the two volumes. Hartley believes that his rules of mental function imply a "rule of life" (Huguelet, xi). That is, he believes his science demonstrates the value of Christian living.

In the eighteenth century and partway into the nineteenth, Observations was popular in "the realm of religious dissent, scientific progress, and social reform" (Allen). Joseph Priestley, a prominent scientist and Unitarian, admired Hartley's "new and most extensive science" (Allen). He called Observations the most important book he had ever read, "the scriptures excepted" (Allen). In his youth Samuel Taylor Coleridge admired Hartley so much that he named his first son after him. Hartley seems to have influenced William Wordsworth as well, but there is no evidence that he actually read him. He may have just heard about his ideas from Coleridge. Later, however, Coleridge changed his views on Hartley. He and other critics, such as the philosopher Thomas Reid, denounced Observations as "conceptually wrong and morally hazardous" (Allen). The main "moral" problem is that Hartley's mechanistic model of the mind seems to deny the existence of free will and thus absolves people of responsibility for their own actions. Hartley, in response to this issue, wrote that despite the implications of his model, "we have a 'practical' free will to do or to resist in most situations involving choice (Huguelet, xi)." For proponents of free will, however, this explanation was insufficient.

In his 1829 essay "Signs of the Times," Thomas Carlyle criticizes contemporary science's emphasis on physical substance over spirit. He criticizes Dr. Cabanis in particular, mentioning Hartley, whom he says "nobody now cares about," only as a contrast. "One would think," he writes, that Hartley's science was "material and mechanical enough." Although this implies that Carlyle favors Hartley over Cabanis, it does not specify the degree of approval. Hartley's science is certainly mechanical, a tendency of which Carlyle disapproves, but it is also "moral science," which he promotes.

The nineteenth-century school of association psychology was the last group to engage seriously with Observations. They considered Hartley the forefather of their science. Being a forefather, however, means being outdated. The founders of association psychology studied Hartley as an important figure in university, but they were the last generation to do so. By the end of the century academic interest in Hartley had disappeared entirely.


Allen, Richard, "David Hartley", The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta (ed.), URL = .

Carlyle, Thomas. The Collected Works of Thomas Carlyle. 16 vols. London: Chapman and Hall, 1858.

Hartley, David. Observations on Man, His Frame, His Duty, and His Expectations. 2 vols. London: S. Richardson, 1749.

Huguelet, Theodore L., Ed. Introduction. Observations on Man, His Frame, His Duty, and His Expectations. By David Hartley. Gainesville: Scholars' Facsimiles & Reprints, 1966.

Last modified 15 March 2009