The question before the human race is, whether the God of nature shall govern the world by his own laws, or whether priests and kings shall rule it by fictitious miracles?
-- John Adams, letter to Thomas Jefferson, June 20, 1815

The United States of America have exhibited, perhaps, the first example of governments erected on the simple principles of nature; and if men are now sufficiently enlightened to disabuse themselves of artifice, imposture, hypocrisy, and superstition, they will consider this event as an era in their history. Although the detail of the formation of the American governments is at present little known or regarded either in Europe or in America, it may hereafter become an object of curiosity. It will never be pretended that any persons employed in that service had interviews with the gods, or were in any degree under the influence of Heaven, more than those at work upon ships or houses, or laboring in merchandise or agriculture; it will forever be acknowledged that these governments were contrived merely by the use of reason and the senses.
-- John Adams, "A Defence of the Constitutions of Government of the United States of America" (1787-88), from Adrienne Koch, ed, The American Enlightenment: The Shaping of the American Experiment and a Free Society (1965) p. 258, quoted from Ed and Michael Buckner, "Quotations that Support the Separation of State and Church"

Thirteen governments [of the original states] thus founded on the natural authority of the people alone, without a pretence of miracle or mystery, and which are destined to spread over the northern part of that whole quarter of the globe, are a great point gained in favor of the rights of mankind.
-- John Adams, "A Defence of the Constitutions of Government of the United States of America" (1787-88), from Adrienne Koch, ed, The American Enlightenment: The Shaping of the American Experiment and a Free Society (1965) p. 258, quoted from Ed and Michael Buckner, "Quotations that Support the Separation of State and Church"

We should begin by setting conscience free. When all men of all religions ... shall enjoy equal liberty, property, and an equal chance for honors and power ... we may expect that improvements will be made in the human character and the state of society.
-- John Adams, letter to Dr. Price, April 8, 1785, quoted from Albert Menendez and Edd Doerr, The Great Quotations on Religious Freedom (1991)

As I understand the Christian religion, it was, and is, a revelation. But how has it happened that millions of fables, tales, legends, have been blended with both Jewish and Christian revelation that have made them the most bloody religion that ever existed?
-- John Adams, letter to FA Van der Kamp, December 27, 1816

The frightful engines of ecclesiastical councils, of diabolical malice, and Calvinistical good-nature never failed to terrify me exceedingly whenever I thought of preaching.
-- John Adams, letter to his brother-in-law, Richard Cranch, October 18, 1756, explaining why he rejected the ministry

I shall have liberty to think for myself without molesting others or being molested myself.
-- John Adams, letter to his brother-in-law, Richard Cranch, August 29, 1756, explaining how his independent opinions would create much difficulty in the ministry, in Edwin S Gaustad, Faith of Our Fathers: Religion and the New Nation (1987) p. 88, quoted from Ed and Michael Buckner, "Quotations that Support the Separation of State and Church"

When philosophic reason is clear and certain by intuition or necessary induction, no subsequent revelation supported by prophecies or miracles can supersede it.
-- John Adams, from Rufus K Noyes, Views of Religion, quoted from from James A Haught, ed, 2000 Years of Disbelief

Indeed, Mr. Jefferson, what could be invented to debase the ancient Christianism which Greeks, Romans, Hebrews and Christian factions, above all the Catholics, have not fraudulently imposed upon the public? Miracles after miracles have rolled down in torrents.
-- John Adams, letter to Thomas Jefferson, December 3, 1813, quoted from James A Haught, ed, 2000 Years of Disbelief

Cabalistic Christianity, which is Catholic Christianity, and which has prevailed for 1,500 years, has received a mortal wound, of which the monster must finally die. Yet so strong is his constitution, that he may endure for centuries before he expires.
-- John Adams, letter to Thomas Jefferson, July 16, 1814, from James A Haught, ed, 2000 Years of Disbelief

I do not like the reappearance of the Jesuits.... Shall we not have regular swarms of them here, in as many disguises as only a king of the gipsies can assume, dressed as printers, publishers, writers and schoolmasters? If ever there was a body of men who merited damnation on earth and in Hell, it is this society of Loyola's. Nevertheless, we are compelled by our system of religious toleration to offer them an asylum.
-- John Adams, letter to Thomas Jefferson, May 5, 1816

Let the human mind loose. It must be loose. It will be loose. Superstition and dogmatism cannot confine it.
-- John Adams, letter to his son, John Quincy Adams, November 13, 1816, from James A Haught, ed, 2000 Years of Disbelief

Can a free government possibly exist with the Roman Catholic religion?
-- John Adams, letter to Thomas Jefferson, May 19, 1821, from James A Haught, ed, 2000 Years of Disbelief

I almost shudder at the thought of alluding to the most fatal example of the abuses of grief which the history of mankind has preserved -- the Cross. Consider what calamities that engine of grief has produced!
-- John Adams, letter to Thomas Jefferson, from George Seldes, The Great Quotations, also from James A Haught, ed, 2000 Years of Disbelief

The priesthood have, in all ancient nations, nearly monopolized learning.... And, even since the Reformation, when or where has existed a Protestant or dissenting sect who would tolerate A FREE INQUIRY? The blackest billingsgate, the most ungentlemanly insolence, the most yahooish brutality is patiently endured, countenanced, propagated, and applauded. But touch a solemn truth in collision with a dogma of a sect, though capable of the clearest proof, and you will soon find you have disturbed a nest, and the hornets will swarm about your legs and hands, and fly into your face and eyes.
-- John Adams, letter to John Taylor, 1814, quoted in Norman Cousins, In God We Trust: The Religious Beliefs and Ideas of the American Founding Fathers (1958), p. 108, quoted from James A Haught, ed, 2000 Years of Disbelief

The Church of Rome has made it an article of faith that no man can be saved out of their church, and all other religious sects approach this dreadful opinion in proportion to their ignorance, and the influence of ignorant or wicked priests.
-- John Adams, Diary and Autobiography

What havoc has been made of books through every century of the Christian era? Where are fifty gospels condemned as spurious by the bull of Pope Gelasius? Where are forty wagon-loads of Hebrew manuscripts burned in France, by order of another pope, because of suspected heresy? Remember the Index Expurgato-rius, the Inquisition, the stake, the axe, the halter, and the guillotine; and, oh! horrible, the rack! This is as bad, if not worse, than a slow fire. Nor should the Lion's Mouth be forgotten. Have you considered that system of holy lies and pious frauds that has raged and triumphed for 1,500 years.
-- John Adams, letter to John Taylor, 1814, quoted by Norman Cousins in In God We Trust: The Religious Beliefs and Ideas of the American Founding Fathers (New York: Harper & Brothers, 1958), p. 106-7, from James A Haught, ed, 2000 Years of Disbelief

God is an essence that we know nothing of. Until this awful blasphemy is got rid of, there never will be any liberal science in the world.
-- John Adams, "this awful blashpemy" that he refers to is the myth of the Incarnation of Christ, from Ira D Cardiff, What Great Men Think of Religion, quoted from James A Haught, ed, 2000 Years of Disbelief

Numberless have been the systems of iniquity The most refined, sublime, extensive, and astonishing constitution of policy that ever was conceived by the mind of man was framed by the Romish clergy for the aggrandizement of their own Order They even persuaded mankind to believe, faithfully and undoubtingly, that God Almighty had entrusted them with the keys of heaven, whose gates they might open and close at pleasure ... with authority to license all sorts of sins and Crimes ... or withholding the rain of heaven and the beams of the sun; with the management of earthquakes, pestilence, and famine; nay, with the mysterious, awful, incomprehensible power of creating out of bread and wine the flesh and blood of God himself. All these opinions they were enabled to spread and rivet among the people by reducing their minds to a state of sordid ignorance and staring timidity, and by infusing into them a religious horror of letters and knowledge. Thus was human nature chained fast for ages in a cruel, shameful, and deplorable servitude....
     Of all the nonsense and delusion which had ever passed through the mind of man, none had ever been more extravagant than the notions of absolutions, indelible characters, uninterrupted successions, and the rest of those fantastical ideas, derived from the canon law, which had thrown such a glare of mystery, sanctity, reverence, and right reverend eminence and holiness around the idea of a priest as no mortal could deserve ... the ridiculous fancies of sanctified effluvia from episcopal fingers.
-- John Adams, "A Dissertation on the Canon and the Feudal Law," printed in the Boston Gazette, August 1765

We think ourselves possessed, or, at least, we boast that we are so, of liberty of conscience on all subjects, and of the right of free inquiry and private judgment in all cases, and yet how far are we from these exalted privileges in fact! There exists, I believe, throughout the whole Christian world, a law which makes it blasphemy to deny or doubt the divine inspiration of all the books of the Old and New Testaments, from Genesis to Revelations. In most countries of Europe it is punished by fire at the stake, or the rack, or the wheel. In England itself it is punished by boring through the tongue with a red-hot poker. In America it is not better; even in our own Massachusetts, which I believe, upon the whole, is as temperate and moderate in religious zeal as most of the States, a law was made in the latter end of the last century, repealing the cruel punishments of the former laws, but substituting fine and imprisonment upon all those blasphemers upon any book of the Old Testament or New. Now, what free inquiry, when a writer must surely encounter the risk of fine or imprisonment for adducing any argument for investigating into the divine authority of those books? Who would run the risk of translating Dupuis? But I cannot enlarge upon this subject, though I have it much at heart. I think such laws a great embarrassment, great obstructions to the improvement of the human mind. Books that cannot bear examination, certainly ought not to be established as divine inspiration by penal laws. It is true, few persons appear desirous to put such laws in execution, and it is also true that some few persons are hardy enough to venture to depart from them. But as long as they continue in force as laws, the human mind must make an awkward and clumsy progress in its investigations. I wish they were repealed. The substance and essence of Christianity, as I understand it, is eternal and unchangeable, and will bear examination forever, but it has been mixed with extraneous ingredients, which I think will not bear examination, and they ought to be separated. Adieu.
-- John Adams, one of his last letters to Thomas Jefferson, January 23, 1825. Adams was 90, Jefferson 81 at the time; both died on July 4th of the following year, on the 50th anniversary of the signing of the Declaration of Independence. From Adrienne Koch, ed, The American Enlightenment: The Shaping of the American Experiment and a Free Society (1965) p. 234. Quoted from Ed and Michael Buckner, "Quotations that Support the Separation of State and Church."

Wilson: Early Presidents Not Religious

"The founders of our nation were nearly all Infidels, and that of the presidents who had thus far been elected [Washington; Adams; Jefferson; Madison; Monroe; Adams; Jackson] not a one had professed a belief in Christianity....
     "Among all our presidents from Washington downward, not one was a professor of religion, at least not of more than Unitarianism."
     -- The Reverend Doctor Bird Wilson, an Episcopal minister in Albany, New York, in a sermon preached in October, 1831. One might expect a modern defender of the Evangelical to play with the meaning of "Christianity," making it refer only to a specific brand of orthodoxy, first sentence quoted in John E Remsberg, Six Historic Americans, second sentence quoted in Paul F Boller, George Washington & Religion, pp. 14-15

The Treaty of Tripoli
Signed by John Adams

"As the government of the United States is not, in any sense, founded on the Christian religion; as it has in itself no character of enmity against the laws, religion or tranquility of Musselmen [Muslims] ... it is declared ... that no pretext arising from religious opinion shall ever product an interruption of the harmony existing between the two countries....
     "The United States is not a Christian nation any more than it is a Jewish or a Mohammedan nation."
          -- Treaty of Tripoli (1797), carried unanimously by the Senate and signed into law by John Adams (the original language is by Joel Barlow, US Consul)