The Age of Reason; Being an Investigation of True and Fabulous Theology is a work by English and American political activist Thomas Paine, arguing for the philosophical position of deism.

The Age of Reason presents common deistic arguments; for example, it highlights what Paine saw as corruption of the Christian Church and criticizes its efforts to acquire political power.

Most deists argued that priests had deliberately corrupted Christianity for their own gain by promoting the acceptance of miracles, unnecessary rituals, and illogical and dangerous doctrines (accusations typically referred to as "priestcraft").

By the middle of the decade, the moderate voices had disappeared: Richard Price, the Dissenting minister whose sermon on political liberty had prompted Edmund Burke's Reflections on the Revolution in France (1790), had died in 1791, and Joseph Priestley had been forced to flee to America after a Church–and–King mob burned down his home and church.

The LCS, which had previously unified religious Dissenters and political reformers, fractured when Francis Place and other leaders helped Paine publish The Age of Reason.

Conceiving ... that I had but a few days of liberty, I sat down and brought the work to a close as speedily as possible; and I had not finished it more than six hours, in the state it has since appeared, before a guard came there, about three in the morning, with an order ... for putting me in arrestation as a foreigner, and conveying me to the prison of the Luxembourg.

[15] When James Monroe, at that time the new American Minister to France, secured his release in 1794,[16] Paine immediately began work on Part II of The Age of Reason despite his poor health.

[18] In the late 1790s, Paine fled from France to the United States, where he wrote Part III of The Age of Reason: An Examination of the Passages in the New Testament, Quoted from the Old and Called Prophecies Concerning Jesus Christ.

All national institutions of churches, whether Jewish, Christian or Turkish, appear to me no other than human inventions, set up to terrify and enslave mankind, and monopolize power and profit.

Urging his readers to employ reason rather than to rely on revelation, Paine argues that the only reliable, unchanging, and universal evidence of God's existence is the natural world.

[34]Using methods that would not become common in Biblical scholarship until the 19th century, Paine tested the Bible for internal consistency, questioned its historical accuracy, and concluded that it was not divinely inspired.

[39][40][41] Paine criticizes the tyrannical actions of the Church as he had those of governments in the Rights of Man and Common Sense, stating that "the Christian theory is little else than the idolatry of the ancient Mythologists, accommodated to the purposes of power and revenue.

"[46] Paine "transformed the millennial Protestant vision of the rule of Christ on earth into a secular image of utopia," emphasizing the possibilities of "progress" and "human perfectibility" that could be achieved by humankind, without God's aid.

[54][55] Though these larger philosophical traditions are clear influences on The Age of Reason, Paine owes the greatest intellectual debt to the English deists of the early 18th century, such as Peter Annet.

In a letter to Elihu Palmer, one of his most loyal followers in America, Paine describes part of his rhetorical philosophy: The hinting and intimidating manner of writing that was formerly used on subjects of this kind [religion], produced skepticism, but not conviction.

[63] Part of what makes Paine's style so memorable is his effective use of repetition and rhetorical questions[63] in addition to the profusion of "anecdote, irony, parody, satire, feigned confusion, folk matter, concrete vocabulary, and .. appeals to common sense".

Having thus made an insurrection and a battle in heaven, in which none of the combatants could be either killed or wounded—put Satan into the pit—let him out again—gave him a triumph over the whole creation—damned all mankind by the eating of an apple, these Christian Mythologists bring the two ends of their fable together.

Bishop Richard Watson, forced to address the new audience in his influential response to Paine, An Apology for the Bible, wrote: "I shall, designedly, write this and the following letters in a popular manner; hoping that thereby they may stand a chance of being perused by that class of readers, for whom your work seems to be particularly calculated, and who are the most likely to be injured by it.

At one sedition trial in the early 1790s, the Attorney–General tried to prohibit Thomas Cooper from publishing his response to Burke's Reflections on the Revolution in France and argued that "although there was no exception to be taken to his pamphlet when in the hands of the upper classes, yet the government would not allow it to appear at a price which would insure its circulation among the people.

For example, he wrote that once one dismisses the false idea of Moses being the author of Genesis, "The story of Eve and the serpent, and of Noah and his ark, drops to a level with the Arabian tales, without the merit of being entertaining.

"[74] Significantly, Watson's Apology directly chastises Paine for his mocking tone: I am unwilling to attribute bad designs, deliberate wickedness, to you or to any man; I cannot avoid believing, that you think you have truth on your side, and that you are doing service to mankind in endeavouring to root out what you esteem superstition.

Davidson and Scheick argue that its "introductory statement of purpose, a fervid sense of inward inspiration, a declared expression of conscience, and an evangelical intention to instruct others" resemble the personal confessions of American Quakers.

"[90] One minister complained that "the mischief arising from the spreading of such a pernicious publication [as The Age of Reason] was infinitely greater than any that could spring from limited suffrage and septennial parliaments" (other popular reform causes).

[86][101] While still in France, Paine formed the Church of Theophilanthropy with five other families, a civil religion that held as its central dogma that man should worship God's wisdom and benevolence and imitate those divine attributes as much as possible.

[102][103] Samuel Adams articulated the goals of this church when he wrote that Paine aimed "to renovate the age by inculcating in the minds of youth the fear and love of the Deity and universal philanthropy.

George Spater explains that "the revulsion felt for Paine's Age of Reason and for other anti-religious thought was so great that a major counter-revolution had been set underway in America before the end of the eighteenth century."

Hailed only a few years earlier as a hero of the American Revolution, Paine was now lambasted in the press and called "the scavenger of faction," a "lilly-livered sinical [sic] rogue," a "loathsome reptile," a "demi-human archbeast," "an object of disgust, of abhorrence, of absolute loathing to every decent man except the President of the United States [Thomas Jefferson].

For such a mongrel between pig and puppy, begotten by a wild boar on a bitch wolf, never before in any age of the world was suffered by the poltroonery of mankind, to run through such a career of mischief.

"[121] The Age of Reason was largely ignored after 1820, except by radical groups in Britain and freethinkers in America, such as Robert G. Ingersoll[122] and the American abolitionist Moncure Daniel Conway, who edited his works and wrote the first biography of Paine, favorably reviewed by The New York Times.

[123] Not until the publication of Charles Darwin's The Origin of Species in 1859, and the large-scale abandonment of the literal reading of the Bible that it caused in Britain did many of Paine's ideas take hold.