Conyers Middleton is one of the "divines" Dr. Gregg Frazer names in his PhD thesis as influencing the theology of the key Founders. As Thomas Jefferson wrote to John Adams, August 22, 1813:
You are right in supposing, in one of yours, that I had not read much of Priestley’s Predestination, his no-soul system, or his controversy with Horsley. But I have read his Corruptions of Christianity, and Early Opinions of Jesus, over and over again; and I rest on them, and on Middleton’s writings, especially his letters from Rome, and to Waterland, as the basis of my own faith. These writings have never been answered, nor can be answered by quoting historical proofs, as they have done. For these facts, therefore, I cling to their learning, so much superior to my own.
Middleton was an English clergyman. Like Jefferson and Adams he (obviously) considered himself a Christian. I don't know of his views on the Trinity (he was certainly greatly admired by many unitarians). What was special about Middleton was his "rationalism." He defended Christianity against deistic thinkers; however he did so while arguing the case of an errant, fallible Bible, one in which man's reason could determine the legitimate parts. The "orthodox" didn't care for Middleton's defense of Christianity. Men like Middleton, Priestley, Jefferson, Adams, probably felt comfortable with a label like "Christian rationalist" (they did use the term "rational Christianity"). But whether this theological system merits the label "Christian" is a matter of debate. It is NOT "Christianity" as the "orthodox" understand the term. The "orthodox" view this system not as "Christian" rationalism but "theistic" or "unitarian" rationalism.
A persistant reader and critic of my work at American Creation pointed to J. Adams' original writings that also endorse the work of Middleton. He researched Adams' quotation where he denied the infallibility of the Bible:
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.
That's how the footnote looks in James Hutson's excellent quote book. However, in reading the original "Prophets of Progress" in context, it's likely that the 1785 refers to the date of John Disney's Memoirs; Adams' comment was likely done later.
Page 290 of "Prophets of Progress" describes the context of Adams' inquiry:
In all likelihood, it was Jefferson's admiration for Conyers Middleton that prompted Adams to make a thorough study of the latter's works, which in turn led him to John Disney's biography of Arthur Sykes, Middleton's inveterate antagonist. Had he read only these two writers, he would already have gained sufficient insight into the theological disputes of the period the half-century extending from Locke to Hume in which the battles between the Low Church and High Church parties were fought out, with the skirmish over Deism thrown in for good measure.
The following passage from "Prophets of Progress" well illustrates the middle ground both Adams and Middleton took that could be at once critical of both orthodoxy Christianity and strict deism:
Matthew Tindal, the Oxford freethinker, had published his Christianity as Old as the Creation, declaring that revelation is superfluous because the religion of nature is perfect in itself. The book drew forth some thirty answers, among them one by Daniel Waterland, vice-chancellor of Cambridge University. Middleton stepped into the controversy with his Letter to Dr. Waterland, showing how Tindal should have been answered. 29 The Letter, of course, made the fray even more violent, starting a separate tussle with Zachary Pearce, the future Bishop of Rochester. Adams seemed satisfied with Middleton's position. The latter charges that Waterland, instead of vindicating the Scriptures, had himself furnished matter for new scandal. [p. 291.]
As theistic rationalists both Middleton and Adams believed both reason and revelation were necessary. As "Prophets of Progress" continues:
Middleton accuses Tindal of attempting to abolish Christianity and set up reason as a national religion. ("Abolish Christianity! Set up reason!" Adams snapped: "The authority of reason is not stern enough to keep rebellious appetites and passions in subjection.") Tindal, Middleton contends, betrayed his ignorance of antiquity by magnifying the moderation of pagan governments. "Deistical cant," Adams reinforced him, adding, "Atheists are the most cruel persecutors.") The intolerance of this "rational Protestant," Middleton jeers, is even worse than Romish popery. ("Deistical popery," Adams chimed in.) [Ibid.]
But still, as theistic rationlists, Adams and Middleton believed reason nonetheless trumped revelation. As Adams put it, reacting to John Disney's thoughts:
D[isney]: The union of all Christians is anticipated, as it has been demonstrated to be the doctrine of Christ, his apostles and evangelists, as also of Moses and the prophets. Nor is it less the language of the religion of nature than of revelation . . .
A[dams]: The human understanding is the first revelation from its maker. From God; from Heaven. Can prophecies, can miracles repeal, annul or contradict that original revelation? Can God himself prove that three are one and one three? The supposition is destructive of the foundation of all human knowledge, and of all distinction between truth and falsehood. [Ibid, p. 297-98.]
This perfectly typifies the "theistic rationalism," key to Founding thought: Reason & revelation were both necessary. Though "nature" discovered by "reason" was the first revelation God gave to man. NOTHING in revelation could contradict the findings of man's reason. Revelation's role was secondary, to support man's reason. Accordingly, reason proves God is unitary not triune in nature. And NOTHING in revelation could be taken seriously to contradict this immutable finding of man's reason. Either interpret revelation to accord with the findings of man's reason, or discard any revelation that doesn't accord with reason as false or corrupted.
Conyers Middleton believed in something similar, in fact, laid the intellectual groundwork for Jefferson and J. Adams to reach such conclusions. The following passage in "Prophets of Progress" sheds light:
Himself accused of atheism, Middleton was threatened with expulsion from Cambridge, where he was Librarian. He composed five or six more essays of similar nature, but wisely decided to keep them in his desk. They were first published in his Works, in 1752, two years after his death. [Ibid, p. 291.]
Middleton's most famous claim was his rejection of all miracles not recorded in scripture, i.e., those claimed by the early Church and subsequent Roman Catholic Church. On miracles, Middleton asserted "the credibility of facts lies open to the trial of our reason and senses." Middleton did not believe "irrational" revelation could come from God. He noted "if any narration can be shown to be false, any doctrine irrational or immoral; 'tis not all the external evidence in the world that can or ought to convince us, that such a doftrine comes from God." He rejected "that every single passage of the Scriptures, we call Canonical, must needs be received as the very word and as the voice of God himself."
Reason, of course, determined which parts of the errant Bible were vaid. The following text, written in 1906 on the history of English rationalism well describes Middleton's rationalist thought:
A volume of essays published after his death showed that Middleton was prepared to criticise the Apostles and Evangelists as fearlessly as he had criticised the Fathers. Peter and Paul were both capable on occasions of dissembling their dearest convictions. The Gospels exhibit irreconcilable discrepancies, proving their authors to have been uninspired and fallible, though honest historians. The gift of tongues did not imply a permanent mastery of foreign languages, and the New Testament is written in very bad Greek. More than a century was to elapse before an English clergyman could again express such opinions with impunity.
This premise of a fallible, partially inspired Bible that must submit to the test of reason "paved the way for a theistic rationalist [Thomas Jefferson] with a pair of scissors to determine for himself what portions of the Bible were legitimately from God...." [Gregg Frazer, PhD thesis, p. 250.]