Twenty Questions is a popular spoken parlour game for two or more players. It encourages deductive reasoning and creativity.

Rules

One player is chosen to be the answerer. That person chooses an object in mind, but does not tell the other players what the object is. All other players are questioners. They each take turns asking a question which can be answered with a simple Yes or No. The answerer answers each question in turn. Sample questions could be "Is it in this room?" or "Is it bigger than a breadbox?"

If a questioner guesses the object, that questioner wins and becomes the answerer for the next round. If twenty questions are asked without a correct guess, then the answerer has stumped the questioners and gets to be the answerer for another round.

Popular variants

The most popular variant is called "Animal, Mineral, Vegetable". In this version, the answerer tells the questioners at the start of the game whether the object is an animal, mineral, or vegetable.

Other versions specify than the thing to be guessed should in a given category, such as actions, occupations, famous people, etc.

Trivia

• The game was turned into a popular radio game show by the BBC in the 1950s. The object to be guessed was revealed to the audience by a "mystery voice". This format was briefly used again on Radio 4 in the 1990s but only lasted one series. A TV version was also made by Associated-Rediffusion in the early 1960s. The "mystery voice" used on the original radio series gave rise to a running joke on the radio series I'm Sorry I Haven't A Clue.

• A version of Twenty Questions is played as a parlor game by characters of Charles Dickens' A Christmas Carol.

• Game theory suggests that the information (as measured by Shannon's entropy statistic) required to identify an arbitrary object is about 20 bits. The game is often used as an example when teaching people about information theory. Mathematically, if each question is structured to eliminate half the objects, twenty questions will allow the questioner to distinguish between 2²⁰ or 1,048,576 objects. Accordingly, the most effective strategy for Twenty Questions is to ask questions that will split the field of remaining possibilities roughly in half each time. The process is analogous to a binary tree search algorithm in computer science.

External links

• 20Q.net (http://www.20q.net/) - Play 20 Questions against the computer with this artificial intelligence version of Twenty Questions. "Everything that it knows and all questions that it asks were entered by people playing the Game."