This letter to his son dated July 7, 1814 clarifies John Adams' position on the inspiration of scripture. He believed parts of the biblical canon were inspired. He thought all modern (as of 1814) translations had errors. He didn't think himself competent in the original languages to judge errors in the original. And he was open to the notion that the writings of John Milton, Homer and Virgil were divinely inspired along the same grounds he believed the inspired parts of the biblical canon were. He admits Song of Solomon and Apocalypse (Book of Revelation) questionably belong in the canon. But, if Homer, Virgil and Milton had a good claim on writing sacred scripture, "those of the Apocalypse and of Solomon’s Song, are unquestionable." He is agnostic on whether St. Jude's Epistle is inspired.
It has been asserted that "rationalists" like John Adams used their reason to determine what was valid revelation. Here is how Adams describes his method:
I am not altogether ignorant, but am far from being properly acquainted with the History of the Bible, or its Evidence; and with regard to its Authority my Mind rests upon two Pillars—the prejudice of my Education; and my own judgment, upon its internal Evidence—You Sir, and my ever dear and honoured Mother, took care to give me a pious education; and although at the same time you sent me upon the theatre of an infidel World, at an age perhaps the most accessible to impressions of infidelity, I never found any thing there, that could serve me as a substitute for the duties or the pleasures, the Morals or the Hopes which I derive from my Religion—I have seen nothing in the glories of this World, nothing in the pride of human learning which should make me ashamed of the Cross of Christ—My Judgment therefore has confirmed the Prejudice of my Education—My idea of Inspiration, as applied to the Scriptures is neither very clear nor very definite—That in the composition of parts of the Sacred Books, the Writers were actuated by a preternatural interposition of the divine power, I believe, because it is expressly declared by the Writers themselves, and because I cannot disbelieve it without rejecting the whole Bible as an imposture.The bold is mine.
*I made a mistake. The letter was from John Quincy Adams to his father. I think a reason I had this brain freeze was as of 1814 John Quincy Adams supposedly had, as many assumed, embraced a form or orthodox Calvinistic Christianity. I assumed wrongly an orthodox Calvinistic Christian would have accepted the plenary inspiration of the biblical canon. He sounds in this letter like a unitarian/theistic rationalist like his father. I will follow up on John Adams the elder's letter to his son that prompted this response.