Disquisitions Relating to Matter and Spirit

[1] Between 1774 and 1778, while he was serving as an assistant to Lord Shelburne, Priestley wrote five major metaphysical works, in which he outlined his materialist philosophy, even though such a position "entailed denial of free will and the soul.

and Dr. Oswald's Appeal (1774),[3] Priestley had strongly suggested that there was no mind-body duality.

Such a position shocked and angered many of his readers who believed that such a duality was necessary for the soul to exist.

In order to explain his belief more clearly Priestley wrote the Disquisitions, which claimed that both "matter" and "force" are active, and therefore that objects in the world and the mind must be made of the same substance.

Although he buttressed his arguments with familiar scholarship and ancient authorities, including scripture, he was labeled an atheist and at least a dozen hostile refutations of the work were published by 1782.