[1] The term "biblical Unitarianism" is connected first with Robert Spears and Samuel Sharpe of the Christian Life magazine in the 1880s.
[7] Their beliefs are based primarily on arguments that both Old Testament and New Testament describe a strictly Unitarian theology with no explicit description of God as three co-equal persons of one substance, and that Trinitarianism is a theory that was developed by some church leaders over the course of centuries, heavily influenced by their contemporary cultures and philosophies.
Historians such as George Huntston Williams (1914–2000) rarely employ the term "biblical Unitarian," as it would be anachronistic.
[13] Nontrinitarianism was against the law until the Doctrine of the Trinity Act 1813, but legal difficulties with the authorities were overcome with the help of barrister John Lee, who later became Attorney General.
Unitarians of this time continued to consider their teachings as "Biblical", though increasingly questioning the inspiration of the Bible and the accounts of the miraculous.
The Summa Universae Theologiae Christianae secundum Unitarios (1787) represents a conservative position which held into the late 19th century.
The New Encyclopædia Britannica notes that the Transcendentalist movement of Ralph Waldo Emerson "shattered rationalist, biblical Unitarianism — now grown conservative — and replaced it with intuitional religion and social idealism.
When Unitarianism spread to the newly opened Middle West, its religious fundamentals changed to human aspiration and scientific truth, rather than Christianity and the Bible.
[19] In the following year, Peter William Clayden's biography of Samuel Sharpe (1883) describes him as a "Biblical Unitarian", adding, "His intensely practical mind, and his business training, joined with his great though rational reverence for the Bible, made him long for definite views expressed in scripture language.
"[24] Alexander Elliott Peaston (1940) pinpoints 1862 as the year of change from "Biblical Unitarianism" to newer models in England,[25][26] where formerly belief in miracles and the resurrection were dominant.
[38] Alongside this historical interest in the Radical Reformation, during the 1990s the term "biblical unitarian" also begins to appear in antitrinitarian publications without either 'b' or 'u' capitalized.