Thomas Jefferson, letter to Thomas Law

"...If we did a good act merely from the love of God and a belief that is pleasing to him, whence arises the morality of the Atheist? It is idle to say, as some do, that no such thing exists. We have the same evidence of the fact as of most of those we act on, to wit: their own affirmations, and their reasonings in support of them. I have observed, indeed, generally that while in Protestant countries the defections from the Platonic Christianity of the priests is to Deism, in Catholic countries they are to Atheism. Diderot, D'Alembert, D'Holbach, Condorcet are known to have been among the most virtuous of men. Their virtue, then, must have had some other foundation than love of God."

Thomas Jefferson, letter to Thomas Law, June 13, 1814

Scanned letter at The Library of Congress