Psychology in the Age of Newton

I argue that the quite dissimilar associationist theories of Hume and Hartley were both strongly influenced by Isaac Newton, who made different methodological recommendations in each of his two major works. Hume, influenced by the Principia Mathematica in which Newton described but refused to hypothesize about a cause of gravity, likewise declines to explain the causes of perceptions or the law-like manner in which they come to be associated. Hartley was influenced by the Optiks, in which Newton speculated that gravitational and other physical forces are transmitted by vibrations. In Hartley’s model, perceptions are vibrations carried from external objects to sense organs, nerves and brain where they give rise to ideas which were attracted, one to another, in a manner he described as associative. The influence of both thinkers on subsequent psychological theory is considered.