Deism (/ˈdiːɪzəm/ DEE-iz-əm  or /ˈdeɪ.ɪzəm/ DAY-iz-əm; derived from Latin "deus" meaning "god") is the philosophical position that rejects revelation as a source of religious knowledge and asserts that reason and observation of the natural world are sufficient to establish the existence of a Supreme Being or creator of the universe.
At least as far back as Thomas Aquinas, Christian thought has recognized two sources of knowledge of God: revelation and "natural reason". The study of the truths revealed by reason is called natural theology. During the Age of Enlightenment, especially in Britain and France, philosophers began to reject revelation as a source of knowledge and to appeal only to truths that they felt could be established by reason alone. Such philosophers were called "deists" and the philosophical position that they advocated is called "deism".
Deism as a distinct intellectual movement declined toward the end of the 18th century and eventually disappeared. Some of its tenets continued to live on as part of other intellectual movements (e.g. Unitarianism) and it continues to have some advocates today.
The words deism and theism are both derived from words meaning "god": Latin deus and Greek theos (θεός). The word déiste first appears in French in 1564 in a work by a Swiss Calvinist named Pierre Viret but was generally unknown in France until the 1690s when Pierre Bayle published his famous Dictionary, which contained an article on Viret.
In English the words "deist" and "theist" were originally synonymous but by the 17th century the terms started to diverge in meaning. The term deist with its current meaning first appears in English in Robert Burton's The Anatomy of Melancholy (1621).
At least since Thomas Aquinas, Christian thought had recognized two valid sources of religious knowledge: divine revelation and natural reason ("natural theology"). During the Enlightenment, some thinkers continued to accept reason, along with features of the natural world, as a valid source of religious knowledge, but they rejected the validity of revelation. These thinkers were the "deists" and the word "deism" refers to their collective attack on the idea of divine revelation.
In effect, deist authors carried out an intellectual war against the idea of revelation. It was a guerilla war in the sense that deist authors operated independently and each author carried out his attacks in his own unique way. Some deist authors attacked with calm logic, while others furiously attacked with moral indignation; some appealed to the facts of history while others wielded pointed humor and sarcasm. These authors exhibited a similarly wide variety of opinions when it came to matters of natural theology. Some believed in the immortality of the soul, posthumous punishment for the wicked, and posthumous rewards for the virtuous; others did not; some were undecided. After Newton published his discoveries, some regarded God as a watch-maker; a distant Creator and First Mover who wound up the universe, set it in motion, and then stepped away; it was pointless to pray to such a God who surely wasn't listening. Others felt a closer connection to God and believed that God heard and responded to their prayers. Those who believed in a watch-maker God rejected the possibility of miracles— after having established natural laws and set the great cosmos in motion, God didn't needed to keep tinkering with his creation. Others accepted the possibility of miracles; God after all was all-powerful and could do anything at all, including temporarily bypassing his own natural laws.
The deists were also animated by a variety of different motives (which at least partially explains the diversity of their concerns and conclusions). This was the age of the Scientific Revolution; some were animated by a new-found respect for science ("natural philosophy") accompanied by a repugnance for superstition, irrationality, and nonsense. Some were saddened and repulsed by the savage religious wars that had been ravaging Europe for decades; their goal was to find a way to stop the fighting. Others were pushing back against the crushing political power possessed by the organized Churches in their respective countries, churches that forbade them from thinking freely, censored them if they tried to publish their thoughts, and (if they could be caught) punished them when they succeeded in publishing.
Details of the deist war on revelation can be found in the article on Deism in England and France in the 18th century. Here we will look at only a few representative deists, in order to show how they illustrate the many personal facets of deism.
The first major statement of deism in English is Lord Herbert of Cherbury's book De Veritate (1624). Herbert, like his contemporary Descartes, searched for the foundations of knowledge. The first two-thirds of his book De Veritate (On Truth, as It Is Distinguished from Revelation, the Probable, the Possible, and the False) are devoted to an exposition of Herbert's theory of knowledge. Herbert distinguished truths obtained through experience and reasoning about experience, from innate truths and from revealed truths. Innate truths are imprinted on our minds, and the evidence that they are so imprinted is that they are universally accepted. Herbert's term for universally accepted truths was notitiae communes – Common Notions. When it came to religion, Herbert believed that there were five Common Notions.
- There is one Supreme God.
- He ought to be worshipped.
- Virtue and piety are the chief parts of divine worship.
- We ought to be sorry for our sins and repent of them
- Divine goodness doth dispense rewards and punishments both in this life and after it.
The appearance of John Locke's Essay Concerning Human Understanding (1690) marks an important turning point, and a new phase, in the history of English deism. Herbert's epistemology was based on the idea of "common notions", in effect, on innate ideas. Locke's famous attack on innate ideas in the Essay effectively destroyed that foundation. After Locke, deists could no longer appeal to innate ideas as Herbert had done. Instead, deists were forced to turn to arguments based on experience and nature. Under the influence of Newton they turned to the argument from design as the principal argument for the existence of God.
Peter Gay identifies John Toland's Christianity not Mysterious (1696), and the "vehement response" it provoked as the beginning of post-Locke deism. Among the notable figures, Gay describes Toland and Matthew Tindal as the best known but as talented publicists rather than philosophers or scholars. He regards Middleton and Anthony Collins as contributing more to the substance of debate; in contrast with fringe writers such as Thomas Chubb and Thomas Woolston.
Other British deists prominent during the period include William Wollastson, Charles Blount, and Henry St John, 1st Viscount Bolingbroke, and, in the latter part, Peter Annet, Thomas Chubb and Thomas Morgan.
Especially noteworthy is Matthew Tindal's Christianity as Old as the Creation (1730), which "became, very soon after its publication, the focal center of the deist controversy. Because almost every argument, quotation, and issue raised for decades can be found here, the work is often termed 'the deist's Bible'." Following Locke's successful attack on innate ideas, Tindal's 'Bible' redefined the foundation of deist epistemology as knowledge based on experience or human reason. This effectively widened the gap between traditional Christians and what he called "Christian Deists", since this new foundation required that "revealed" truth be validated through human reason.
Enlightenment deism consisted of two philosophical assertions: (a) reason, along with features of the natural world, is a valid source of religious knowledge, and (b) revelation is not a valid source of religious knowledge. Different deist authors expanded on these two assertions to create what Leslie Stephen later termed the "constructive" and "critical" aspects of deism. "Constructive" assertions— assertions that deist writers felt were justified by appeals to reason and features of the natural world (or perhaps were intuitively obvious) — included: 
- God exists and created the universe.
- God gave humans the ability to reason.
"Critical" assertions— assertions that followed from the denial of revelation as a valid source of religious knowledge— were much more numerous. They included:
- Rejection of all books, including the Bible, that are claimed to contain divine revelation.
- Rejection of the incomprehensible notion of the Trinity and other religious "mysteries".
- Rejection of reports of miracles, prophecies, etc.
All deists rejected the Bible as a book of divine revelation. If you define "a Christian" as a person who accepts the stories in the Bible as true, divine revelations, the deists were not Christians. They rejected the miracle stories in the Bible and rejected the divinity of Jesus. Many, however, accepted Jesus as an actual historical person and held him in high regard as a moral teacher. (This position is known as Christian deism and was Thomas Jefferson's motive for assembling his famous Jefferson Bible.) On the other hand, if you define "a true Christian" as a person regards the historical human person Jesus as a great moral teacher and attempts to follow Jesus' moral teachings, many deists considered themselves to be true Christians. Some deists were of the opinion that Jesus taught timeless moral truths, that those moral truths were the essence of Christianity, and since those truths are timeless they predate Jesus' teachings. This was the premise of Matthew Tindal's Christianity as Old as the Creation.
A central premise of deism was that the religions of their day were corruptions of an original religion that was pure, natural, simple, and rational. Humanity lost this original religion when it was subsequently corrupted by "priests" who manipulating it for personal gain and for the class interests of the priesthood in general, and thus encrusted with superstitions and "mysteries" – irrational theological doctrines. They referred to this manipulation of religious doctrine as "priestcraft," an intensely derogatory term.
They declared that laymen were thus kept dependent on the priesthood for information about the requirements for salvation, and baffled by these "mysteries" – giving the priesthood a position of great power, which they worked to maintain and increase. Deists saw it as their mission to strip away "priestcraft" and "mysteries". Tindal, perhaps the most prominent deist writer, claimed that this was the proper original role of the Christian Church.
One implication of this premise was that current-day primitive societies, or societies that existed in the distant past, should have religious beliefs less encrusted with superstitions and closer to those of natural theology. (This position became less and less plausible as thinkers such as David Hume began studying the natural history of religion and suggested that the origins of religion lay not in reason but in the emotions, specifically fear of the unknown.)
Different deists had different beliefs about the immortality of the soul, about the existence of Hell and damnation to punish the wicked, and the existence of Heaven to reward the virtuous. Anthony Collins, Bolingbroke, Thomas Chubb, and Peter Annet were materialists and either denied or doubted the immortality of the soul. Benjamin Franklin believed in reincarnation or resurrection. Lord Herbert of Cherbury and William Wollaston, held that souls exist, survive death, and in the afterlife are rewarded or punished by God for their behavior in life. Thomas Paine believed in the "probability" of immortality of the soul.
Influenced by Newton's cosmology, many deists regarded God as a distant Creator who wound up the universe, set it in motion, and then stepped away. These deists naturally considered it to be pointless to pray to or worship a God who surely wasn't listening. Others, however, felt a closer connection to God and believed that God heard and responded to their prayers.
The most natural position for deists was to reject all forms of supernaturalism, including the miracle stories in the Bible. The problem was that the rejection of miracles seemed to entail the rejection of divine providence, of God taking a hand in human affairs— something that many did not want to reject. Those who believed in a watch-maker God rejected the possibility of miracles and divine providence— after establishing natural laws and setting the cosmos in motion, God stepped away. He didn't need to keep tinkering with his creation, and the suggestion that he did was insulting to Him. Others, however, firmly believed in divine providence and so were reluctantly forced to accept at least the possibility of miracles; God after all was all-powerful and could do whatever he wanted, including temporarily bypassing his own natural laws.
Enlightenment thinkers, under the influence of Newtonian science, tended to view the universe as a vast machine, created and set in motion by a creator being, that continues to operate according to natural law, without any divine intervention. This view naturally led to what was then called necessitarianism (the modern term is determinism): the view that everything in the universe – including human behavior – is completely causally determined by antecedent circumstances and natural law. (See, for example, La Mettrie's L'Homme machine  .) As a consequence, debates about freedom versus "necessity" were a regular feature of Enlightenment religious and philosophical discussions. Reflecting the intellectual climate of the time, there were differences among deists about freedom and determinism. Some, such as Anthony Collins, actually were necessitarians.
Views differ on whether David Hume was a deist, an atheist, or something else. Like the deists, he had no truck with revelation, and his famous essay "On Miracles" provided a powerful argument against belief in miracles. On the other hand, he had no truck with the idea that an appeal to Reason could provide any justification for religion. In Natural History of Religion (1757) he contends that polytheism, not monotheism, was "the first and most ancient religion of mankind" and that the psychological basis of religion is not reason, but fear of the unknown. Hume's account of ignorance and fear as the motivations for primitive religious belief was a severe blow to the deist's rosy picture of prelapsarian humanity basking in priestcraft-free innocence. In Waring's words
Until 1776 the (now) United States were colonies of the British empire and Americans, as British subjects, were influenced by and participated in the intellectual life of England and Great Britain. English deism was an important influence on the thinking of Thomas Jefferson and the principles of religious freedom asserted in the First Amendment to the United States Constitution. Other "Founding Fathers" who were influenced to various degrees by deism were Ethan Allen, Benjamin Franklin, Cornelius Harnett, Gouverneur Morris, Hugh Williamson, James Madison, and possibly Alexander Hamilton.
In the United States, where the Culture Wars still rage, there is a great deal of controversy over whether the Founding Fathers were Christians, deists, or something in between. Particularly heated is the debate over the beliefs of Benjamin Franklin, Thomas Jefferson, and George Washington.
In his "Autobiography" Franklin wrote that as a young man "Some books against Deism fell into my hands; they were said to be the substance of sermons preached at Boyle's lectures. It happened that they wrought an effect on me quite contrary to what was intended by them; for the arguments of the Deists, which were quoted to be refuted, appeared to me much stronger than the refutations; in short, I soon became a thorough Deist." Like some other deists, Franklin believed that, "The Deity sometimes interferes by his particular Providence, and sets aside the Events which would otherwise have been produc'd in the Course of Nature, or by the Free Agency of Man," and stated at the Constitutional Convention that "the longer I live, the more convincing proofs I see of this truth -- that God governs in the affairs of men."
Thomas Jefferson is perhaps the Founding Father who most clearly exhibits deist tendencies, although he generally referred to himself as a Unitarian rather than a deist. His excerpts of the Biblical gospels, for example, now commonly known as the Jefferson Bible, strips away all supernatural and dogmatic references from the Christ story. Like Franklin, Jefferson believed in God's continuing activity in human affairs. 
Thomas Paine is especially noteworthy both for his contributions to the cause of the American revolution and to the cause of deism. His The Age of Reason (Parts I and II in 1794 and 1795) was short, readable, and is probably the only deist tract that continues to be read, and to be influential, today. 
The last contributor to American deism was Elihu Palmer (1764–1806), who wrote the "Bible of American deism", Principles of Nature, in 1801. Palmer is noteworthy for attempting to bring some organization to deism by founding the "Deistical Society of New York" and other deistic societies from Maine to Georgia.
France had its own tradition of religious skepticism and natural theology in the works of Montaigne, Bayle, and Montesquieu. The most famous of the French deists was Voltaire, who was exposed to Newtonian science and English deism during his two-year period of exile in England (1726-8). When he returned to France he brought both back with him, and exposed the French reading public (i.e. the aristocracy) to them in a number of books.
- the increasing influence of naturalism and materialism
- the writings of David Hume and Immanuel Kant raised questions about the ability of reason to address metaphysical questions.
- the violence of the openly-deistic French Revolution
- Christian revivalist movements, such as Pietism and Methodism, which emphasized a personal relationship with god, along with the rise of anti-rationalist and counter-Englightenment philosophies such as that of Johann Georg Hamann
It is correct to say that deism declined, in the sense that use of the word "deism" declined. But it would be incorrect, or at least misleading, to say that deism died— deist ideas and influences lived on. One of the major activities of the deists, biblical criticism, evolved into its own highly technical discipline. Deist rejection of revealed religion evolved into, and contributed to, 19th-century liberal British theology and the rise of Unitarianism.
The 2001 American Religious Identification Survey (ARIS) survey estimated that between 1990 and 2001 the number of self-identifying deists grew from 6,000 to 49,000, representing about 0.02% of the US population at the time. The 2008 ARIS survey found, based on their stated beliefs rather than their religious identification, that 70% of Americans believe in a personal God, roughly 12% are atheist or agnostic, and 12% believe in "a deist or paganistic concept of the Divine as a higher power" rather than a personal God.
The term "ceremonial deism" was coined in 1962 and has been used since 1984 by the Supreme Court of the United States to assess exemptions from the Establishment Clause of the First Amendment to the U.S. Constitution, thought to be expressions of cultural tradition and not earnest invocations of a deity. It has been noted that the term does not describe any school of thought within deism itself.
In 1993, Bob Johnson created the World Union of Deists (WUD) which offered a monthly paper publication THINK! and two online deist publications, THINKonline! and Deistic Thought & Action! In 1996 WUD launched its web site deism.com  . In 1998 the Virginia/Tennessee affiliate of WUD created the Sullivan-County.com  web site to promote more traditional deist views.
A WUD defines deism this way.
In 2009, the World Union of Deists published a book on deism, Deism: A Revolution in Religion, A Revolution in You written by its founder and director, Bob Johnson. This book focuses on what deism has to offer both individuals and society. In 2010 the WUD published the book An Answer to C.S. Lewis' Mere Christianity, which is a rebuttal to the book Mere Christianity by the Christian apologist C.S. Lewis. In 2014, the WUD published its third book, God Gave Us Reason, Not Religion, which describes the difference between God and religion, and promotes innate reason as God's greatest gift to humanity, other than life itself. It proposes that people can have belief in The Supreme Intelligence/God that is beyond a reasonable doubt.
The World Union of Deists in 2016 became a producer of the film adaptation of Ian Ruskin's play To Begin the World Over Again: The Life of Thomas Paine  . The film includes important coverage of Thomas Paine's profound Deism and his work to promote Deism.
The Positive Deism movement began in 2004. Historically and to the present day, deists have been very critical of the revealed religions as well as trying to be constructive. Positive Deists focus their efforts solely on being constructive and avoid criticism of other faiths. In 2009 Chuck Clendenen, one of its adherents, published a book entitled "Deist: so that's what I am!". The aim of the book was to educate those who believed similarly but were unfamiliar with the words "deism" and "deist".
In 2010, the Church of Deism (not affiliated with the World Union of Deists) was formed in an effort to extend the legal rights and privileges of more traditional religions to Deists while maintaining an absence of established dogma and ritual.
Contemporary deism attempts to integrate classical deism with modern philosophy and the current state of scientific knowledge. This attempt has produced a wide variety of personal beliefs under the broad classification of belief of "deism."
There are a number of subcategories of modern deism, including monodeism (this being the default standard concept of deism), pandeism, spiritual deism, process deism, Christian deism, polydeism, scientific deism, and humanistic deism. Some deists see design in nature and purpose in the universe and in their lives. Others see God and the universe in a co-creative process. Some deists view God in classical terms and see God as observing humanity but not directly intervening in our lives, while others see God as a subtle and persuasive spirit who created the world and then stepped back to observe. Most contemporary deists do not believe in divine intervention, but some still find value in prayer as a form of meditation, self-cleansing, and spiritual renewal.
In the 1960s, theologian Charles Hartshorne scrupulously examined and rejected both deism and pandeism (as well as pantheism) in favor of a conception of God whose characteristics included "absolute perfection in some respects, relative perfection in all others" or "AR", writing that this theory "is able consistently to embrace all that is positive in either deism or pandeism", concluding that "panentheistic doctrine contains all of deism and pandeism except their arbitrary negations".
Charles Taylor, in his 2007 book A Secular Age, showed the historical role of deism, leading to what he calls an exclusive humanism. This humanism invokes a moral order, whose ontic commitment is wholly intra-human, with no reference to transcendence. One of the special achievements of such deism-based humanism is that it discloses new, anthropocentric moral sources by which human beings are motivated and empowered to accomplish acts of mutual benefit. This is the province of a buffered, disengaged self, which is the locus of dignity, freedom and discipline, and is endowed with a sense of human capability. According to Taylor, by the early 19th century this deism-mediated exclusive humanism developed as an alternative to Christian faith in a personal God and an order of miracles and mystery. Some critics of deism have accused adherents of facilitating the rise of nihilism.