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Handing a decision to chance is one of the oldest ways to make one. The Athenian democracy of the fifth century BC filled most public offices by lot rather than by vote, and from the fourth century used a stone machine, the kleroterion, to do it: citizens' bronze tickets were slotted into columns and a row was accepted or rejected depending on whether a white or black ball rolled out of a tube beside it. Sortition was not a shortcut. It was the point — a magistrate chosen by lot owed nobody a favour.

Cleromancy, the reading of lots as answers from a god, is older still and runs through the Hebrew Urim and Thummim, the Chinese I Ching with its yarrow stalks and coins, and the Roman sortes drawn at the oracle of Praeneste. In each case the mechanism is the same as this page: a question, a random pick, an answer.

The twenty-answer oracle is a specific object. In 1946 Albert Carter of Cincinnati, whose mother was a clairvoyant, built a liquid-filled tube called the Syco-Seer with a twenty-sided die floating inside; each face carried a reply that pressed against a window when the tube was tipped. Carter's business partner Abe Bookman refined it, and in 1950 the Chicago company Brunswick Billiards commissioned a version shaped like a black eight-ball for a promotion. That shape stuck. Mattel bought the rights in 1971 and the toy entered the US National Toy Hall of Fame in 2018.

The die inside is an icosahedron with ten affirmative, five non-committal and five negative faces. Any answer this page gives in oracle mode is one of those twenty, in exactly that proportion.

주요 성질

• In yes/no mode each answer is a fair Bernoulli trial, so the count of "yes" in n answers follows the binomial distribution B(n, ½).
• With "maybe" included the three answers are equally likely, one in three each; the chance of a straight yes or no on one ask falls from ½ to ⅓.
• The oracle draws from twenty replies: ten affirmative (50%), five non-committal (25%) and five negative (25%). It is not a fair coin.
• The chance of the oracle giving the same reply twice in a row is 1 in 20; of three identical replies in a row, 1 in 400.
• Because the seed defaults to the question text, rewording a question — even by one character — is a fresh draw. Asking the identical question again returns the identical answer.
• Seeded output is reproducible by design, which is the opposite of what a real oracle promises: nothing here knows anything about the question.

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• The kleroterion of Athens, reconstructed from fragments found in the Agora, selected the 500 members of the Boule and the jurors of the courts; several fragments are displayed in the Agora Museum.
• Chapter 4 of the Book of Jonah and 1 Samuel 14 both describe lots cast to settle a question, the biblical form of yes-or-no divination.
• The eight-ball oracle appears in films from Toy Story to Interstellar and has a Google Easter egg: searching "magic 8 ball" shows a shakeable one.
• Modern sortition is back in use: citizens' assemblies in Ireland (2016–18) and France (2019–20) were selected by lot, stratified to match the population.
• Coin-toss decisions in sport — the cricket toss, the NFL overtime toss — are yes/no draws by convention, trusted because they are seen to be made in the open.