The following passage, from the opening pages of Thomas Paine’s The Age of Reason has always been one of my favorites. Here, Paine famously lays out the tenets of his religious belief in simple, stirring language:

“I believe in one God, and no more; and I hope for happiness beyond this life.

“I believe the equality of man, and I believe that religious duties consist in doing justice, loving mercy, and endeavouring to make our fellow creatures happy.”

It’s easy to see why these words, clear and heartfelt, are so often quoted. But as usual, Paine is only getting started. Next comes a set of caveats and clarifications:

“But lest it should be supposed that I believe many other things in addition to these, I shall, in the progress of this work, declare the things I do not believe, and my reasons for not believing them.

“I do not believe in the creed professed by the Jewish church, by the Roman church, by the Greek church, by the Turkish church, by the Protestant church, nor by any church that I know of. My own mind is my own church.

“All national institutions of churches, whether Jewish, Christian, or Turkish, appear to me no other than human inventions set up to terrify and enslave mankind, and monopolize power and profit.”

Again as usual, Paine leaves us with no doubt as to exactly where he stands on the subject of religion. But it’s what comes next that is, for me, not just the most interesting, but the truly revolutionary part of Paine’s argument. Here, Paine the critical thinker steps beyond the language of creed (“I believe”) and begins to address — and then to question — the nature of belief itself.

“I do not mean by this declaration to condemn those who believe otherwise. They have the same right to their belief as I have to mine. But it is necessary to the happiness of man, that he be mentally faithful to himself. Infidelity does not consist in believing, or in disbelieving: it consists in professing to believe what he does not believe.

“It is impossible to calculate the moral mischief, if I may so express it, that mental lying has produced in society. When a man has so far corrupted and prostituted the chastity of his mind, as to subscribe his professional belief to things he does not believe, he has prepared himself for the commission of every other crime. He takes up the trade of a priest for the sake of gain, and in order to qualify himself for that trade, he begins with a perjury. Can we conceive any thing more destructive to morality than this?”

Paine points out the dangers of what we would today call self-deception — what he, more bluntly, calls “mental lying.”

In fact, throughout The Age of Reason, as in so much of his work Paine insists on the need to interrogate belief: to ask ourselves exactly where our beliefs come from, why we hold to them — and where they may lead us. For Paine, received wisdom on any subject is always, always — something to be questioned, and frequently something to be resisted.