God. He criticised those whose faith was shaped by books and fashion, drawing an analogy between the scepticism of educated men and the credulity of the masses. Maintaining that humans had no free will, Priestley argued that what he called "philosophical necessity" (akin to absolute determinism) is consonant with Christianity, a position based on his understanding of the natural world. Like the rest of nature, man's mind is subject to the laws of causation, Priestley contended, but because a benevolent God created these laws, the world and the people in it will eventually be perfected. Evil is therefore only an imperfect understanding of the world. Although Priestley's philosophical work has been characterised as "audacious and original", it partakes of older philosophical traditions on the problems of free will, determinism, and materialism. For example, the 17th-century philosopher Baruch Spinoza argued for absolute determinism and absolute materialism. Like Spinoza and Priestley, Leibniz argued that human will was completely determined by natural laws; unlike them, Leibniz argued for a "parallel universe" of immaterial objects (such as human souls) so arranged by God that its outcomes agree exactly with those of the material universe. Leibniz and Priestley share an optimism that God has chosen the chain of events benevolently; however, Priestley believed that the events were leading to a glorious millennial conclusion, whereas for Leibniz the entire chain of events was optimal in and of itself, as compared with other conceivable chains of events. Founder of British Unitarianism When Priestley's friend Theophilus Lindsey decided to found a new Christian denomination that would not restrict its members' beliefs, Priestley and others hurried to his aid. On 17 April 1774, Lindsey held the first Unitarian service in Britain, at the newly formed Essex Street Chapel in London; he had even designed his own liturgy, of which many were critical. Priestley defended his friend in the pamphlet Letter to a Layman, on the Subject of the Rev. Mr. Lindsey's Proposal for a Reformed English Church (1774), claiming that only the form of worship had been altered, not its substance, and attacking those who followed religion as a fashion. Priestley attended Lindsey's church regularly in the 1770s and occasionally preached there. He continued to support institutionalised Unitarianism for the rest of his life, writing several Defenses of Unitarianism and encouraging the foundation of new Unitarian chapels throughout Britain and the United States. Experiments and Observations on Different Kinds