Hartley’s Naturalization of the Mind

Allen’s book entitled David Hartley on Human Nature (1999) gives a careful review of the works and life of the physician and philosopher David Hartley (1705-1757). However, there has been no thorough study of the role of nerves in the naturalisation of the mind in Hartley’s work. This latter, in his Observations on Man, his Frame, his Duty, and his Expectations first published in 1749, discusses the nature of sensations and ideas. Thereby, he takes position on famous notions of physics, physiology, and psychology of his time. In following the account of association in John Gay’s Dissertation on the Fundamental Principles of Virtue, which states the possibility to explain mental pleasures and plains on the basis of association, Hartley wants to show the physical cause of this latter, as well as its moral consequences. He is very inspired by Newton, both for the theory of vibrations, and the conception of nerves as capillary. Rejecting Boerhaave’s idea of tubular nerves in which the animal spirits flow, he sketches nerves as constituted by infinitesimal particles vibrating in aether. Although his explanation of sensations, ideas, and motions, is strictly materialist, Hartley insists on their mental status. By accounting for mental facts with considerations about infinitesimal material processes, the philosopher is able to show that associations of ideas actually have the power to modify the vibrating structure of our brain. It is interesting to see, from a historical point of view, how far Hartley takes the Lockean project of naturalisation of the mind.