Abstract

In this paper I show how what came to be known as “the double law of habit,” first formulated by Joseph Butler in a discussion of moral psychology in 1736, was taken up and developed by medical physiologists William Porterfield, Robert Whytt, and William Cullen as they disputed fundamental questions regarding the influence of the mind on the body, the possibility of unconscious mental processes, and the nature and extent of voluntary action. The paper shows, on a particular topic, the overlap between eighteenth-century philosophical writings on the science of human nature on the one hand,and medical writings and lectures in physiology on the other. Other early modern writers discussed in the paper include René Descartes, Herman Boerhaave and David Hume.