Deism is belief in a God or first cause based on reason, rather than on faith or revelation, and thus a form of theism in opposition to fideism. Deism is usually synonymous with natural religion in 18th century Enlightenment writings. Deism originated in 17th century Europe, gaining popularity in the 18th century Enlightenment especially in America as a modernist movement inspired by the success of the scientific method. Deists emphasize the exclusive application of reason and personal experience to religious questions. Deism is concerned with those truths which humans can discover through a process of reasoning, independent of any claimed divine revelation through scripture or prophets.
Most Deists believe that that the universe was created by a God who then makes no further intervention in its affairs, often expressed by the metaphor of the "Divine Watchmaker" with creation being self-regulating. Deists do not maintain that the reason God does not intervene in the world (via miracles) is because he does not care, but rather that he has already created the best of all possible worlds and any intervention could not improve it.
Some other religions, such as Roman Catholicism, believe also that the existence of God can be known via reason, but also claim that miracles and revelations happen.
Deism and Theism are closely related and this sometimes leads to controversy. The root of the word "deism" is from the Latin "deus", while the root of the word "theism" comes from the Greek "theos", both meaning "god" in English. In practice there are a range of beliefs encompassed by both Theism and Deism; however, Theism can include faith or revelation as a basis for belief while Deism can include only belief which can be substantiated through reason.
18th century popularity
Deism developed in response to Newtonian physics, by which matter is seen to behave in a manner mathematically predictable by natural laws. It was popular among thinkers of the Enlightenment such as Voltaire and the Founding Fathers of the United States. Perhaps deistic thinkers were impressed by Newton's apparent demonstration that reason could finally settle problems that formerly were thought to be permanently controversial, and thus hoped to also settle religious questions permanently and scientifically by reason alone, without revelation.
Newtonian physics is rather deterministic, and so Deism based on that might not seem like it has much room for hope. Of some relevance in response to this are newer theories in physics, most notably quantum mechanics, which has both a non-deterministic interpretation (the Copenhagen interpretation), and deterministic interpretations (the transactional interpretation and many-worlds interpretation).
Thomas Jefferson and Benjamin Franklin are perhaps the most well-known of the American founding Deists. Thomas Paine published The Age of Reason, a tract that popularized Deism throughout America and Europe.
Appellations for divinity
The names used for the divinity by Deists include the following:
Decline in popularity
Several factors contributed to a general decline in the popularity of Deism, including: