Armed with this doctrine, Jefferson could do battle with any notion that religious profession or belief was necessary for good citizenship, or was even a proper question for public inquiry. We would do well to let it alone. The practical effect of Jefferson’s analysis, while deistic in formal structure, was a thoroughgoing secularism. Having retained deity as a postulate only of nature’s orderliness and moral lawfulness, Jefferson’s system did not, and could not, look beyond secular values and consequences for its conception of the good. Beyond the secular realm – “nature,” in Jefferson’s parlance – no light came. A purer agnosticism could hardly be framed, except for retention of a purely hypothetical primordial Creator that had set the universe upon its orderly course, a necessary closure of their logic to account for the origin of a perfect self-regulating system of natural order.
Theologians once debated whether deism was a species of theism or a disguised denial of theism – an atheism in Sunday dress. It appears in this context that as Jefferson and deists of his persuasion understood it, deism shared with the revealed religions (theism as expressed in both Judaism and Christianity) only the elements of belief in (I) a universe manifesting intelligent design in its structure and operation and (2) a monillaw, which theists based on revelation, but which deists insisted human beings could know through the combined functions of intuition and reason. (The popular writers on deism, including Jefferson, as lay philosophers were not entirely consistent in relating the rational and the intuitive in human nature.) With the deity removed to the purely theoretical position of an axiom of their science, they produced the first ideologically powerful expression in modern times of a consistently secular world view. Religion retained its place in the privacy of the heart – primarily as a reflective piety born of gratitude for the gift of being – but theology was retired in favor of scientific investigation. That deism lies in spirit on the agnostic-naturalistic side of the theological watershed is illustrated in the popular literature of religious polemic. The most virulent attacks upon deists have come from supernaturalists, while the most spirited defenders of the deists throughout the 19th and 20th centuries have been skeptics and secularists. Jefferson himself knew where the battle line was drawn; his greatest biographer, Dumas Malone, has written that Jefferson from his youth hated supernaturalism and that, as the years lengthened, his attitude became one of bitterness.
The conclusion that we draw from this history is that modern humanism as we know it in the English-speaking world and throughout much of the West -for all its departures from Lollardry, Roundhead radical nonconformity, and grassroots deism of the militant variety preached by Paine, (or the more sophisticated form discreetly held by Jefferson and his circle) – this humanism is a legitimate living branch of the old populist tree.