In addition to other medical works he published anonymously Conjectures sur les memoires originaux dont it parait que Moyse s'est servi pour composer le livre de la Genese, (1753), in which he pointed out that two main sources can be traced in the book of Genesis; and two dissertations on the immateriality and immortality of the soul,.
Like Plato, he believed in real Universals, real essences, real causes; he believed in the unity of the universal, and in the immateriality of essences; he believed in the good, and that there is a good of the universe; he believed that God is a living being, eternal and best, who is a supernatural cause of the motions and changes of the natural world, and that essences and matter are also necessary causes; he believed in the divine intelligence and in the immortality of our intelligent souls; he believed in knowledge going from sense to reason, that science requires ascent to principles and is descent from principles, and that dialectic is useful to science; he believed in happiness involving virtue, and in moral virtue being a control of passions by reason, while the highest happiness is speculative wisdom.
In 1778 appeared a published correspondence between these two liberal theologians on the subjects of materialism and necessity, wherein Price maintains, in opposition to Priestley, the free agency of man and the unity and immateriality of the human soul.
These contain an account of the well-known experiment in which he sought to establish the immateriality of heat by showing its generation through the friction of two pieces of ice in an exhausted vessel, and further attempt to prove that light is "matter of a peculiar kind," and that oxygen gas, being a compound of this matter with a simple substance, would more properly be termed phosoxygen.
Accordingly, when the work was published at Paris in August 1641, under the title of Meditationes de prima philosophia ubi de Dei existentia et animae immortalitate (though it was in fact not the immortality but the immateriality of the mind, or, as the second edition described it, animae humanae a corpore distinctio, which was maintained), the title went on to describe the larger part of the book as containing various objections of learned men, with the replies of the author.