Materialism in Eighteenth-Century European Thought

John Toland (1670–1722) was born Catholic, though he converted to Protestantism and later endorsed Socinianism, which, like Unitarianism, denied the doctrine of the Trinity. He wrote several texts in which he supported a naturalized and historical interpretation of the holy texts and of miracles. In Christianity not Mysterious (1696) he claimed that reason is sufficient to explain all religious "mysteries." In Letters to Serena (1704) and Pantheisticon (1720), he endorsed a form of pantheism in which God-soul is identical with the material universe. He defended Giordano Bruno (1548–1600), whose pantheistic and materialistic philosophy obviously influenced him. Pantheism was the doctrine that God was everywhere and was all things.

Anthony Collins (1676–1729) was a provocative author who argued, in his Discourse of Free-thinking (1713, published anonymously), that free and rational inquiry is the best defense for religion against atheism. In Inquiry concerning Human Liberty and Necessity (1715) and Liberty and Necessity (1729), he denied free will and defended determinism on the grounds of the necessity of a cause-and-effect relationship between events. He wrote A Letter to Mr. Dodwell (1707), to which Samuel Clarke, Newton's disciple, responded. This led to a two-year correspondence (1706–1708) in which Toland defended the idea that all life and consciousness arises from emergent properties of systems of material particles.

David Hartley (1705–1757) saw himself as carrying out Newton's scientific project for the human being and offered a physiological explanation for the association of ideas in materialistic terms in his Observations on Man: His Frame, His Duty, and His Expectations (1749). Hartley used Newton's theory of vibrating corpuscular matter and forces of attraction and repulsion as a metaphysical basis for Locke's associationist psychology. He explained mental life in terms of associations and inhibitions, which themselves were to be explained by attraction and repulsion in the nervous system and the brain. Hartley, however, was a deeply religious thinker who believed that "theopathy," the love of God, was a natural emotion, and whose depiction of salvation bordered on mysticism.

Joseph Priestley (1733–1804) was a freethinker who formally rejected Calvinism to enter the Unitarian denomination. Priestley is known mainly for his work in physics and chemistry. He consistently pursued science as a rational enterprise based on facts and experimentation, rather than on dogmatic principles. His view of nature was informed by his belief in a benevolent God who operates through laws of nature that become accessible through careful observation. While this belief in God somehow influenced Priestley's heuristics, his work in chemistry and physics and his political and economic theories were informed by a methodological materialism in which only matter and natural laws were relevant. Between 1772 and 1790, he published six volumes of Experiments and Observations on Different Kinds of Air and several papers in the Philosophical Transactions of the Royal Society, of which he was a member. He is well known for his contributions to the chemistry of gases, and for his development of a theory of phlogisticated air (which was opposed to Lavoisier's, who repeated Priestley's experiments, and rejected the phlogiston theory in favor of his new oxygen theory).