What Dr. Gregg Frazer termed "theistic rationalism" -- the religious creed of the key Founders -- contains a number of elements that distinguish it from both Christianity and Deism. They include theological unitarianism (denial of the Trinity), universalism (universal salvation, the good rewarded immediately with bliss, the bad punished temporarily, eventually redeemed), syncretism (most or all religions are valid ways to God), and the notion that the Bible is partially inspired (thus errant) and that man's reason is the ultimate device for discerning which parts of the Bible are true, which are not. The system also posits an active personal God and the efficacy of prayer; in fact, the theistic rationalists were more likely to call themselves "Christians" than "Deists."
This was without question the creed of Jefferson, Adams, and Franklin, and very likely Madison, Washington, G. Morris, Wilson, Hamilton (before his end of life conversion to orthodox Christianity) and countless other lesser Founders whose religious beliefs have yet to have been subject the rigorous historical examination necessary to determine what they really believed. This has not yet been done. All that has been shown is the overwhelming majority of them were formally or nominally associated with Christian churches which, in their official creeds, professed orthodoxy. And yet, theistic rationalists like Jefferson, Adams and Franklin likewise were formally or nominally associated with such churches. In Adams' case, his "Puritan" Congregation preached unitarianism from the pulpit as of 1750.
A reader skeptical of this theory asked whether Adams believed the Bible was errant or man's reason trumped revelation before the 1800s when he resumed his correspondence with Jefferson. The answer is yes. I've written about it here. In 1785, Adams wrote:
What suspicions of interpolation, and indeed fabrication, might not be confuted if we had the originals! In an age or in ages when fraud, forgery, and perjury were considered as lawful means of propagating truth by philosophers, legislators, and theologians, what may not be suspected?
-- John Adams, marginal note in John Disney’s Memoirs (1785) of Arthur Sykes. Haraszti, Prophets of Progress, 296. Taken from James H. Hutson, The Founders on Religion, p. 26.
Adams was so suspicious of the accuracy of the Bible's text that he doubted it contained the correct version of the Ten Commandments. Notice how he uses terms like "error" and "amendment" to describe what's contained in the Bible:
When and where originated our Ten Commandments? The Tables and The Ark were lost. Authentic copies, in few, if any hands; the ten Precepts could not be observed, and were little remembered.
If the Book of Deuteronomy was compiled, during of after the Babilonian Captivity, from Traditions, the Error or Amendment might come in there.
-- John Adams to Thomas Jefferson, Nov. 14, 1813.
Adams makes clear that the "corruptions of Christianity" had seeped into the Bible:
We have now, it seems a National Bible Society, to propagate King James’s Bible, through all Nations. Would it not be better, to apply these pious subscriptions, to purify Christendom from the corruptions of Christianity, than to propagate these corruptions in Europe, Asia, Africa, and America!
-- John Adams to Thomas Jefferson, November 4, 1816. Taken from James H. Hutson, The Founders on Religion, p. 143.
And of course, in 1787-1788, Adams declared that the United States was founded on man's reason and the senses, and a treaty from his administration declared the United States was in no sense founded on the Christian religion.
Likewise the reader accepted Jefferson's unitarianism but was skeptical about Jefferson's syncretism. Jefferson's 1809 letter to James Fishback evinces his belief in the validity of most or all world religions:
Every religion consists of moral precepts, and of dogmas. In the first they all agree. All forbid us to murder, steal, plunder, bear false witness &ca. and these are the articles necessary for the preservation of order, justice, and happiness in society. In their particular dogmas all differ; no two professing the same. These respect vestments, ceremonies, physical opinions, and metaphysical speculations, totally unconnected with morality, and unimportant to the legitimate objects of society. Yet these are the questions on which have hung the bitter schisms of Nazarenes, Socinians, Arians, Athanasians in former times, and now of Trinitarians, Unitarians, Catholics, Lutherans, Calvinists, Methodists, Baptists, Quakers &c. Among the Mahometans we are told that thousands fell victims to the dispute whether the first or second toe of Mahomet was longest; and what blood, how many human lives have the words 'this do in remembrance of me' cost the Christian world! We all agree in the obligation of the moral precepts of Jesus; but we schismatize and lose ourselves in subtleties about his nature, his conception maculate or immaculate, whether he was a god or not a god, whether his votaries are to be initiated by simple aspersion, by immersion, or without water; whether his priests must be robed in white, in black, or not robed at all; whether we are to use our own reason, or the reason of others, in the opinions we form, or as to the evidence we are to believe. It is on questions of this, and still less importance, that such oceans of human blood have been spilt, and whole regions of the earth have been desolated by wars and persecutions, in which human ingenuity has been exhausted in inventing new tortures for their brethren. It is time then to become sensible how insoluble these questions are by minds like ours, how unimportant, and how mischievous; and to consign them to the sleep of death, never to be awakened from it. ... We see good men in all religions, and as many in one as another. It is then a matter of principle with me to avoid disturbing the tranquility of others by the expression of any opinion on the [unimportant points] innocent questions on which we schismatize, and think it enough to hold fast to those moral precepts which are of the essence of Christianity, and of all other religions. [My emphasis.]
Jefferson also made clear that good people of all religions get into Heaven because of their works. From his September 18, 1813 letter to William Canby:
I believe...that he who steadily observes those moral precepts in which all religions concur, will never be questioned at the gates of heaven, as to the dogmas in which they all differ. That on entering there, all these are left behind us, and the Aristides and Catos, the Penns and Tillotsons, Presbyterians and Baptists, will find themselves united in all principles which are in concert with the reason of the supreme mind.
Aristides and Cato were pagans. The pagan Cato was George Washington's hero. Indeed, when called upon to explain his belief in the afterlife, Washington invoked a pagan authority for such. From his letter to Annis Boudinot Stockton 31 August 1788:
But with Cicero in speaking respecting his belief of the immortality of the Soul, I will say, if I am in a grateful delusion, it is an innocent one, and I am willing to remain under its influence....I can never trace the concatenation of causes, which led to these events, without acknowledging the mystery and admiring the goodness of Providence. To that superintending Power alone is our retraction from the brink of ruin to be attributed.
Washington certainly doesn't sound like an orthodox Christian in that passage. Indeed, he, like the other theistic rationalist American Founders were imbibed in pagan Greco-Romanism. You have to wonder why, if they were almost all committed orthodox Christians, the, for instance, authors of the Federalists Papers (Hamilton, Madison, and Jay) would choose a pagan Greco-Roman surname -- "Publius" -- as opposed to a Hebraic one. Jay was perhaps the only orthodox Christian out of those three. But he wrote a measly five essays compared to Hamilton's fifty-one and Madison's twenty-nine. And in any event, though the series has a few nominal references to a generic "Providence," there is no mention of Jesus, the Bible or citations of verses and chapters of Scripture. If the US Constitution had any connection whatsoever to the Bible or "Christian principles," that series would seem the perfect place to so tell us. But they don't.