Eric Alan Isaacson, a member of the Unitarian Universalist Church, unsuccessfully tried to leave this message at Positive Liberty. He was responding to my comment about the difference between theological unitarianism and creedal Unitarianism (or lower case "u" unitarianism v. capital "U" Unitarianism). That is, while some ministers in the Congregational Church (and other Protestant denominations as well) preached theological unitarianism, mid-18th century in churches which heretofore had orthodox Trinitarian creeds, I noted that the Congregational Churches in Massachusetts really didn't begin to change their creeds to "Unitarian" until the early 19th century. This has led many folks to mistake unitarianism as a 19th Century phenomenon, when it was really an 18th Century one.
A problem with my assessment is that Unitarianism, back then as today, was defined by such wide latitudinarianism that it adopted no official creeds. So "creedal" Unitarianism is sort of an oxymoron. Yet, churches in Massachusetts did become, in the 19th Century, officially "Unitarian" Churches.
Mr. Isaacson elaborates the details:
I guess the word "creed" has a multiplicity of meanings - - ranging from the formal statements of faith (generally rejected by Unitarians) to rather informal and general summaries of people's beliefs.
If you're looking for legal precedent, I think you'll find that the New Hampshire Supreme Court insisted that Unitarians have a creed when, in 1868, it disqualified Dover's First Unitarian Society of Christians' chosen minister - - as insufficiently "Christian." See Hale v. Everett, 53 N.H. 9, 16 Am. Rep. 82, 1868 N.H. LEXIS 47 (1868).
My understanding is that Congregationalist churches in Eastern Massachusetts were by the mid-eighteenth century very liberal in their theology - - but that their ministers had little interest in making an issue of that liberal theology.
It was Calvinist conservatives who made an issue of the urban churches' theological drift, charging early in the nineteenth century that the liberal ministers were Unitarians, and refusing to exchange pulpits with them.
It's hard to peg a specific date for the schism between Unitarian and Trinitarian Congregationalists. Some might point to the 1801 split in the Plymouth Congregation as the schism's beginning. Others may point to the 1805 appointment of Henry Ware to the Hollis Chair of Divinity at Harvard - - which induced orthodox Calvinists to organize the Andover Theological Seminary in 1808. Still others might point to 1815, when the Calvinist Rev. Jedidiah Morse published an excerpt from Thomas Belsham's 1812 "Life of Theophilus Lindsey," outing New England's liberal ministers as heretical Unitarians.
Disfellowshipped by conservative Calvinists, the liberal ministers and their congregations eventually embraced the Unitarian designation, with William Ellery Channing preaching his sermon on "Unitarian Christianity" in 1819.
The conservatives' efforts to ensure orthodoxy had backfired. When all was said and done, New England's oldest and most historic Protestant churches were in the Unitarian Camp - - including the Mayflower Pilgrims' First Parish Church in Plymouth, and John Winthrop's First Church in Boston, the spiritual beacon for his "city on a hill." All but one of Boston's historic Congregationalist churches landed firmly in the Unitarian camp.
Here's a link to a Unitarian Universalist explanation of the "Unitarian Controversy," which I believe owes much to George Willis Cooke's book.
Please note that the Unitarian congregations never tried to exclude Trinitarians on doctrinal or creedal grounds. Rather, Calvinist Trinitarians systematically disfellowshipped and shunned the religious liberals, condemning and isolating them as Unitarian heretics - - and the liberals eventually responded by embracing the name.
Today the liberal congregations are members of a denomination that celebrates human diversity and spiritual freedom within and among its religious communities.
As for the conservative churches in the Congregationalists' nineteenth-century schism - - they today are members of the United Church of Christ, perhaps the most liberal of America's "mainline" Trinitarian denominations.
And despite our little family squabble, most Unitarian Universalists today regard the United Church of Christ with considerable pride, as our sibling denomination.
Eric Alan Isaacson