Pascal's Wager

The Wager is a fragment in the Pensées (Thoughts) of Blaise Pascal, published in 1670, eight years after his death at age 39. Pascal had planned a defense of Christianity and left hundreds of notes, which friends at Port-Royal edited into a book. The passage, headed Infinite, nothing, argues that reason cannot decide whether God exists. But you must wager, because you are already on board and cannot stay out. If you wager that God exists and are right, you gain an infinite reward, and if you are wrong, you lose almost nothing. If you wager against and are right, you gain a little, and if wrong, you lose everything. So, a rational person should bet on God.¹²

Pascal was among the founders of probability theory, working with Fermat in 1654 to solve problems of gambling, and the Wager applies expected-value reasoning to faith. He imagines the reader objecting that he cannot make himself believe. Pascal answers that one can act as if one believed, taking holy water and having masses said, and that the habits will gradually change the mind. He was also a Jansenist Catholic, whose convictions came from Augustine, and a physicist of the barometer. In November 1654, he had a religious experience that he recorded on a scrap of parchment starting with the word Fire and sewed into his coat.¹²

Critics say the argument fails because there are many possible gods, because belief cannot be chosen at will, and because infinite payoffs break expected-value reasoning. Even so, the Wager helped create decision theory, and philosophers still argue about it.¹²