This is another post of mine from 2008 on John Adams' response to one Jedidiah Morse on the concept of Unitarianism.Adams was a fervent theological unitarian who militantly and bitterly rejected the doctrine of the Trinity. In 1815, he gets a letter from one Jedidiah Morse who attacked unitarianism, which was then growing in popularity.
Adams responded with an FU letter featured that you can read in its entirety here. To his credit, Adams tries to occupy a reasonable middle ground between the Trinitarian Calvinist fundamentalist "orthodoxy" Morse was trying to enforce and the more radical philosophical deism that was in the "air" of that era.
When Adams uses the term "Athanasianism," he refers to the traditional Trinitarian orthodoxy of St. Athanasius who defended the Nicaean creed in 325AD against Arius (Adams was on Arius' side). Athanasius also later first (meaning he literally was the first early church father or figure to do so) articulated the 27 books of the New Testament as an exclusive list in 367 AD (something Adams mistakenly thought was done in Nicaea; and Adams didn't have any kind of confidence in the biblical canon partly because of such).
But on to Adams' quotation:
... More than fifty years ago, I read Dr. Clarke, Emlyn, and Dr. Waterland: do you expect, my dear doctor, to teach me any thing new in favour of Athanasianism? — There is, my dear Doctor, at present existing in the world a Church Philosophick. as subtle, as learned, as hypocritical, as the Holy Roman Catholick, Apostolick, and Ecumenical Church. The Philosophical Church was originally English. Voltaire learned it from Lord Herbert, Hobbes, Morgan, Collins, Shaftsbury, Bolingbroke, &c. &c. &c. You may depend upon it, your exertions will promote the Church Philosophick, more than the Church Athanasian or Presbyterian. This and the coming age will not be ruled by inquisitions or Jesuits. The restoration of Napoleon has been caused by the resuscitation of inquisitors and Jesuits.I am and wish to beYour friend,JOHN ADAMSQuincy, May 15th, 1815.