Although Locke and Hume had used the principle of association to explain many of the more developed mental contents and processes, Hartley carried their ideas to a new point of comprehensiveness. Like them, he considered the mind a tabula rasa-that is, a blank slate-prior to the experience of sensation, but he extended the laws of mental growth through contiguous associations to include all mental phenomenon -memory, imagination, reason, and the emotions. He argued that developed or complex emotions were the products of elementary feelings uniting and passing into new connections, and giving rise to complex emotions, under the general law of contiguity. (Reductionism). These emotions in turn, became motivators, in a behavioristic fashion of positive reinforcement and punishment. (Hedonism)

Hartley's theory dealt with the physical nature of sensation; derived from Sir Isaac Newton. Hartley argued that any sensation of the external world sets up a vibratory motion in the nerve affected, producing corresponding vibrations in the cerebral substance; he assumed that impulses directed from the brain to the muscles proceed in the same manner. Vibratruncles, were physical manifestation of ideas - A primitive stab at the neural make up of the brain, which in fact IS changed, chemically and physically, during learning. Hartley was correct.