Observations on Man

Observations on Man, his Frame, his Duty, and his Expectations is 18th-century British philosopher David Hartley's major work. Published in two parts in 1749 by Samuel Richardson, it puts forth Hartley's principal theories: the doctrine of vibrations and the doctrine of associations. The first part of the text deals with the frame of the human body and mind, and their mutual connections and influences, the second with the duty and expectations of mankind.

Hartley's physical theory was drawn from certain speculations as to nervous action which Isaac Newton had published in his Principia (1687). Elements of Hartley's psychological theory were suggested by other writers, such as John Gay. For example, "in Hartley's theory, emotion is a fluid like electricity or water"—it flows from one experience to the next, a concept he called transference and lifted from the writings of Gay. Although Hartley acknowledges that Gay "put me upon considering the power of association" in relation to transference, he developed a different theory of association from Gay′s.

Like John Locke, Hartley asserted that, prior to sensation, the human mind is a tabula rasa. Beginning with simple sensations, the mind eventually forms advanced states of consciousness. Hartley 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.

Hartley believed that sensation is the result of vibrations of the minute particles of the medullary substance of the nerves, made possible by a subtle, elastic ether that was rare in the interstices of solid bodies and in their close neighbourhood. Pleasure was the result of moderate vibrations and pain of violent vibrations, sometimes so violent that they broke the continuity of the nerves. These vibrations left behind a tendency to fainter vibrations or "vibratiuncles" of a similar kind in the brain, which corresponded to "ideas of sensation." This accounted for memory.

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