When once we quit the basis of sensation, all is in the wind. To talk of immaterial existences is to talk of nothings. To say that the human soul, angels, god, are immaterial, is to say they are nothings, or that there is no god, no angels, no soul. I cannot reason otherwise: but I believe I am supported in my creed of materialism by Locke, Tracy, and Stewart.{Letter to John Adams, from Monticello, 15 August 1820}

The legitimate powers of government extend to such acts only as are injurious to others. It does me no injury for my neighbor to say there are twenty gods or no god. It neither picks my pocket nor breaks my leg.

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 the love of God.[Letter to Thomas Law, 13 June 1814]

To talk of immaterial existences is to talk of nothings. Tosay that the human soul, angels, god, are immaterial, is tosay they are nothings, or that there is no god, no angels,no soul. I cannot reason otherwise .. . without plunginginto the fathomless abyss of dreams and phantasms. I amsatisfied, and sufficiently occupied with the things whichare, without tormenting or troubling myself aboutthose which may indeed be, but of which I have noevidence.

Question with boldness even the existence of aGod; because, if there be one, he must more approve ofthe homage of reason than that of blindfolded fear.

It is always better to have no ideas than false ones; to believe nothing, than to believe what is wrong.

I have ever judged of the religion of others by their lives... But this does not satisfy the priesthood. They must have a positive, a declared assent to all of their interested absurdities. My opinion is that there would never have been an infidel, if there had never been a priest.

I am anxious to see the doctrine of one god commenced in our state. But the population of my neighborhood is too slender, and is too much divided into other sects to maintain any one preacher well. I must therefore be contented to be an Unitarian by myself, although I know there are many around me who would become so, if once they could hear the questions fairly stated.

Nothing but free argument, raillery and even ridicule will preserve the purity of religion.