Tic-tac-toe
A solved two-player game with a forced draw under optimal play.
Tic-tac-toe, also known as noughts and crosses or Xs and Os, is a paper-and-pencil game for two players who take turns marking spaces in a three-by-three grid. It is a solved game with a forced draw assuming best play from both players, and has been used as a pedagogical tool for teaching game theory and artificial intelligence.
- also_known_as
- Noughts and crosses (Commonwealth English), Xs and Os (Canadian or Irish English)
- type
- Paper-and-pencil game
- players
- 2
Lore & Background
An early variation, terni lapilli, was played in the Roman Empire around the first century BC, where each player had only three pieces and moved them to empty spaces. The US renaming to 'tic-tac-toe' occurred in the 20th century.
Reader's Guide
Tic-tac-toe is significant as one of the simplest games to be solved by artificial intelligence, often used to teach the minimax algorithm and game tree searching. The game's combinatorics show that with best play, it always ends in a draw, making it a futile game for perfect players.
Did You Know?
- The game is a solved game, with a forced draw assuming best play from both players.
Frequently Asked Questions
Who is Tic-tac-toe?
Tic-tac-toe is a two-player paper-and-pencil game where opponents alternately claim cells on a 3×3 grid, trying to get three of their marks in a row. Depending on region it also goes by noughts and crosses (Commonwealth English) or Xs and Os (Canadian/Irish English).
What are Tic-tac-toe's powers/role?
Its defining trait is that it is a fully solved game: neither side can force a victory if both play optimally, so the outcome is always a draw. Because of that, it has become a staple teaching example in game theory and a classic benchmark problem in artificial-intelligence research.
How does Tic-tac-toe's story end?
Under best play from both players, every match resolves as a stalemate—no one can compel a win. That guaranteed draw is precisely what makes the game 'solved' in the mathematical sense.
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