The Beginnings of Priestley's Materialism

The mature materialism of Joseph Priestley's Disquisitions relating to Matter and Spirit of 1777 is based on three main arguments: that Newton's widely-accepted scientific methodology requires the rejection of the 'hypothesis' of the soul; that a dynamic theory of matter breaks down the active/passive dichotomy assumed by many dualists; and that interaction between matter and spirit is impossible. In Matter and Spirit it is the first two arguments which are given greatest prominence; but it is the third argument which first brought Priestley to take materialism seriously. It was an argument which had persistently troubled him in his dualist years, but it was not until 1774 in the Examination that he 'first entertained a serious doubt of the truth of the vulgar hypothesis'. Underlying this fact is an episode of some complexity which this article examines.