David Hartley FRS (/ˈhɑːrtli/; baptized 21 June[citation needed] 1705 Old Style; died 28 August 1757) was an English philosopher and founder of the Associationist school of psychology.

Hartley was educated at Bradford Grammar School and in 1722 was admitted as a Sizar to Jesus College, Cambridge, where he was a Rustat scholar.

The couple moved to Bury St Edmunds, and Alice died there giving birth to their son David Hartley (the Younger) (1731–1813).

Although one point at issue may have been the doctrine of the Trinity, Hartley's main dissent from Anglican orthodoxy was his assent to universal reconciliation.

In the same letter to Lister, Hartley writes that "a Man who disregards himself, who entirely abandons Self-Interest & devotes his Labours to the Service of Mankind, or in that beautiful and expressive phrase of the Scriptures, who loves his neighbor as himself is sure to meet with private Happiness".

By the time of his move to London in 1736, Hartley was known by other campaigners of variolation, such as Hans Sloane and James Jurin, president of the Royal Society.

A bladder stone, sometimes as large as an egg, could function as a ball-cock on a toilet tank, causing an inability to urinate, excruciating pain, and sometimes death.

Hartley thought a herbalist called Joanna Stephens had developed a lithontriptic, an oral medicine that would dissolve a stone in situ.

Hales had shown that some bladder stones rapidly dissolved in boiled soap-lye (caustic potash, potassium hydroxide).

What was needed, then, was a safely ingestible preparation that would turn a person's urine alkaline; and this, they concluded, is what the slaked lime and soap combination did.

In 1739 Hales won the Copley Medal for his work, and the following year Hartley published their results in a Latin volume, De Lithontriptico, in Basel and Leiden, the latter being home at the time to the foremost medical school in Europe.

He continued to practise medicine, and he devoted himself to writing his major work, Observations on Man, His Frame, His Duty, and His Expectations, published in 1749 by Samuel Richardson.

[12] As one would expect from a physician with an inquiring mind and active medical practice, Hartley draws together a wide range of observations – to name a few, on phantom limbs, savant syndrome, and the experiences and mental development of the blind and the deaf (OM 1, props.

An initial defensive gesture becomes a general aggressive stance, and thus the source of the insulting words and threatening actions by which the adult "goes on multiplying perpetually … the occasions of anger and the expressions of it".

He was, rather, a religious visionary, and his fundamental belief breathtakingly optimistic: that association "has a tendency to reduce the state of those who have eaten of the tree of the knowledge of good and evil, back again to a paradisiacal one" (OM 1.1.2.14, Cor.

Hartley's physical theory gave birth to the modern study of the intimate connection of physiological and psychical facts.

He believed 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.

[15] Starting from a detailed account of the phenomena of the senses, Hartley tried to show how, by the above laws, all the emotions, which he analyses with considerable skill, may be explained.

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.