Deism is a theological theory proposing that a god created the Universe but is an All-Powerful Bystander who has since refrained from any activity in it. It was espoused by many European scientific thinkers of the 18th century (the Enlightenment age), some leaders of The French Revolution, namely Maximilien Robespierre, and some US founding fathers such as Benjamin Franklin, Thomas Jefferson and Thomas Paine.
Essentially, you can view it as God, or the Supreme Being, created the Universe, set up all the laws of reality and everything, then either totally lost interest or simply stepped aside to let his creation run its course without interruption. He's still "around", but he doesn't do much, if anything, to interfere with mortal lives (And if He did, we mere mortals probably wouldn't be in the loop; after all, God Works In Mysterious Ways...). In other cases, God/the Supreme Being was essentially nature or a linguistic substitute for the system of natural laws that governed the world, and it can be described in the manner a computer program or operating system today is described.
The ideology extols a reasoned evaluation of scientific evidence as supporting a rationally ordered universe, but not revelation, any absolute moral code or any miracles. It was the more acceptable equivalent of modern atheism during the Enlightenment, rejecting any accounts about miracles or revelation until proven (e.g. Jefferson is controversial for creating a revision of the Bible without any miracles), and espouses that science and reason are the most reliable ways to know the Creator.
The reason why this skepticism manifested itself in a kind of inverted substitute for Christianity and established religion is a cause for some debate. Deists met in salons for congregation, read Enlightened works by Locke and Rousseau in place of scripture, and later, the likes of Robespierre and Thomas Paine started actual deist festivals and temples, one of the reasons why later atheists and secular liberals and revolutionaries (as well as the more radical of their contemporaries) saw them as hypocritical, silly and wishy-washy fence-sitters. The reasons for this are more cultural than anything. Religion, and Christianity in particular, wasn't just a set of beliefs, it was also part of the culture, it had festivals, it had days on calendars marked with saints, it was part of the language, swear words and slang, it had carols, it had great art and architecture, as well as the rituals of the Catholic Church which attracted many people towards it. In France, there had never been a successful Protestant Reformation, and the Church was a heavy part of the culture and attitudes. Deism as well as its parallel off-shoots like Freemason lodges offered a space for intellectuals and curious people to be free of Christian culture and influence. Secular nationalism was greatly inspired by Deism's attempt to create a parallel room for a social life that did not revolve around religion.
Classical Deism is similar to modern deism in that they're both based on reason and naturalism, but classical Deism's evolution from Christianity is more readily apparent. Classical Deism didn't have the benefit of evolution, the big bang theory, or even an idea of how old the earth and universe were. Newton's theory of gravity and Copernicus's heliocentric model of the universe were the best they had to go on, hence why they believed in intelligent design. They viewed God as transcendental from its creation and impersonal, preferring neither the Catholic, nor Protestant nor the extremely anti-sexual and anti-liberty models of morality. However, at the time deism was part of a continuum with Christianity. Christian Deism and Unitarianism were situated in the middle, but they were for the most part more individualistic or utilitarian. When conservatives cite the references about a Creator in their defense of the founding fathers being Christian, liberals in response cite the lack of scientific knowledge at the time as the reason why the founding fathers still referenced a Creator, even though it was obvious for them that religious interference in politics would directly contradict the Bill of Rights (the First Amendment has "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof", and hell definitely counts under the prohibited "cruel and unusual punishment").
Deism never really became popular among the lower-classes despite attempts to proselytize and popularize it by the likes of Paine and Robespierre. It was seen as too elitist and too intellectual and its attempts to create ritual celebrations such as the notorious Festival of the Supreme Being were so controversial that it alienated its original support base among the emerging middle-class. The turn of the century saw the Second Great Awakening in America and Christian revival in other areas of the world, while Napoleon on ascending to power brought back the Catholic Church to its former place of pride in French society. In the end, its biggest impact and influence was its anti-clerical and critical views of organized religion and Christianity. While atheist authors did exist, for the most part their arguments of Religion Is Wrong did not catch a wide audience or be treated as anything more than a "shock" or "scandal" among the educated elite, they were seen even by non-believers as pranksters rather than someone posing a real challenge to the Church.
Deist authors by arguing for a natural religion based on then-scientific knowledge, by being "for" something provided a more coherent argument, at the time, to live a non-Christian secular life. During the French Revolution, deists had wide support from liberal aristocrats and middle and lower-middle class people as well as working class agitators, while atheist radicals were quite famous for attacking and destroying Church property and even threatening pro-revolutionary priests such as Henri Gregoire (who wanted a liberal Catholic Church, clamped down on antisemitism and campaigned for abolitionism) during the dechristianizing campaign. Robespierre, a famous Deist, managed to clamp down on excesses of dechristianization, by stating that "atheism is aristocratic" seeing it as a viewpoint that essentially states that common people are idiotic for having religious sentiment. Nationalism during the Revolution often had a quasi-religious fervor where people saw democracy and The Enlightenment as new doctrines for a non-denominational Church. The American Founders, having more time, distance and a less hostile partisan climate than in France, used Deist ideas of a distant god guiding human endeavors in science and politics to create a comprehensive precisely written separation of Church and State in the First Amendment that kept the State as non-intervening and non-hostile to religious belief. They were helped by the fact that the Catholic Church wasn't omnipresent as it was in France (it was the largest landowner pre-Revolution) and many of the Protestant sects had a strong liberal dissenting tradition since they were persecuted by the Anglican Church in England.
Some like Voltaire was highly critical of Church superstitions and his writings in Candide, Zadig, The Ingenu enjoyed a wider audience than the author of the atheist pamphlet, "The Three Imposters". Likewise, it was Thomas Paine who wrote the widely read and popular The Age of Reason, which provided Biblical criticism from a Deist perspective that was widely read by most readers. While Deists such as Voltaire was critical of atheism as well note , a lot of his arguments and ideas, as well as that of Paine's inspired later atheist writers and authors. In the course of the 19th Century, later scientific developments such as Darwin's evolutionary theory as well as leftist, anarchist and Marxist critique led to the development of an atheism that was accessible and viable to the common man. Darwin's theory of evolution by natural selection ended the need for a rational conception of an anthropomorphic creator of mankind. Post-Einsteinian and quantum physics have ironically eroded some of the original science-based ideas of deism, i.e. that the natural laws of the universe are fixed and stable, rather than relative to time and space (as argued by Einstein), or that knowledge can be derived from observation of natural phenomenon (where quantum mechanics argue that on the subatomic level, the act of observation affects the quantity of the thing being observed).
The '90s saw a revival in Deism facilitated by the Internet. This form of Deism is known as Modern Deism and it is no longer the liberated and enlightened worldview; Atheism displaced it from this position, and currently Deism fills a middle niche, along with Agnosticism, both of which are attacked by religious and atheists as "fence-sitters". Modern Deism incorporates what science has discovered since the enlightenment and holds the nature of God is unknowable other than that God exists. In fact, Modern Deists are encouraged to use reason to determine God's nature for themselves.
Modern variations include:
- Pandeism: which incorporates Pantheism, the archetype for Pieces of God
- Christian Deism: a hybrid between Christian and Deist beliefs. It rejects Jesus's divinity and other supernatural claims of the Bible but stands by Jesus's moral teachings, holding him up as Christian Deism's central philosopher
- Polydeism: the universe is a creation of more than one god, but all have since left the building.
- Arthur C. Clarke
- It is the prevailing religion in the last installment of his 2001: A Space Odyssey novels. Everyone in 3001 believes "as little as possible", and the big split is between Theists, who believe "in at least one god", and Deists, who believe "in at most one god". Deists believe in one god or none, depending on whether an inactive god "counts" as such — but not more than one, because if God is outside space and time and doesn't do anything, if there were two of Him, what would make them distinct?
- Also used in the Rama Series, although again it's not really present until the last installment, Rama Revealed (and a little bit in The Garden of Rama). The creatures who built Rama did so as part of a project to collect life from all over the universe, to learn about God's plan for it, and are committed Deists.
- British statesman Lord Chesterfield tended to this position, as shown in the Letters to His Son: "The object of all the public worships in the world is the same; it is that great eternal Being who created everything." (letter 29) He writes that Lord Bolingbroke also was this: "He professes himself a deist; believing in a general Providence, but doubting of, though by no means rejecting (as is commonly supposed) the immortality of the soul and a future state." (letter 95)
- The god of Star Maker could be this, though that one is so callous to the suffering going on in the Universe as to seem downright malevolent.
- Double Standard: Some deists despite criticizing religion and Christianity for intolerance and superstition nonetheless kept many of its prejudices. Voltaire was an influential challenger of censorship and the Church's censorship, he was also a rabid antisemite. Likewise, the Roman nostalgia of this time amounted to a simplistic identification with the pagan aristocracy of Ancient Rome on the part of Edward Gibbon and others, and uncritically accepting Roman and Greek defenses of slavery and class subjugation.
- Older Than Feudalism : Associated with the Enlightenment, but the idea originates in Ancient Greece, and some even find traces in Akhenaten.
- Outgrown Such Silly Superstitions : Much Deist literature is about how silly are theistic ideas of revelations, miracles, talking snakes, virgin births, etc. By now, Deism has largely died out as a common Enlightened theological position now that there are solid naturalistic explanations for the creation of the world, since there is no longer a logical requirement for a creator to explain it. This has led to endless debates of what the positions of famous historical deists would have been if they lived today.
- Sacred Scripture:
- Averted, as Deism rejects entirely the notion that a God has authored or inspired any sort of religious text, instead positing that such texts are always human inventions, and that God's only 'communication' to man is our Universe itself, the operations of which are discoverable through our gifts of reason and science.
- Some Deists considered the works of the Enlightenment as The Moral Substitute for scripture, namely the works of Voltaire, Jean-Jacques Rousseau as well as several classical texts. This was especially apparent during The French Revolution where they converted the Neoclassical Church of Ste. Geneviève into the Pantheon, a mausoleum for the graves of great thinkers and a posthumous-Hall of Fame, that essentially made them into secular saints for veneration.
- Slavery Is a Special Kind of Evil:
- Averted by the Founding Fathers, who were deists but also slave-owners and often invoked "reason" as justification for human bondage, believing that they were enlightened masters and accepting racism on (now discredited) pseudo-scientific grounds, which often made Deism a form of Intellectually Supported Tyranny.
- The French deists and sympathisers were more consistently abolitionist on the other hand, albeit allying with Christian intellectuals like Abbe Gregoire and Abbe Raynal in calling for the end of slavery and advocating anti-racism, during the French Revolution.
- Take a Third Option : Some people say deism splits the line between atheism and theism (though initially it was the second option to theism). Others like this wiki say it's a form of theism.