Chess is especially popular for its complexity. The number of legal positions in chess is estimated to be 1043; the number of possible games is a lot larger and greatly exceeds the estimated number of particles in the observable universe.
Each player is given sixteen pieces which are arranged in the opening position on a 64-square chess board. The players alternate moves (one has the White pieces and moves first, the other has the Black pieces). The object of the game is checkmate, a situation where the opponent's king is threatened with capture and has no way out. A position in which the king is threatened with capture (but has a way out) is called check; a player can never move a king into and must always rescue a king from such a position.
If a player is not in check and has no legal move, then the situation is called stalemate and the game ends as a draw. If fifty moves (twenty-five on each side) are played without a piece being taken or a pawn moved, the game also ends as a draw. Repeating the same board position for a third time creates a draw; however, this rule does not often lead to "ko threats" as in Go.
The most powerful piece is the queen. The queen can move in a straight line in any of eight directions unless blocked by another piece. In contrast, rooks can move in a straight line only in non-diagonal directions, and bishops can move in a straight line only in diagonal directions.
"Castling" involves moving the king two spaces toward a rook of the same color and moving the rook to the space immediately beyond the king. It protects the king and brings out the rook for action. It must be the first move that the king and the rook make, there must be no other pieces in the way, and the king cannot move into, out of, or through check.
: : : : : : : : : : : : : : : : : : +---+---+---+---+---+---+---+---+ __\ +---+---+---+---+---+---+---+---+ | R | | | | K | B | | R | / | | | K | R | | B | | R | +---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+ Queen-side castling
: : : : : : : : : : : : : : : : : : +---+---+---+---+---+---+---+---+ __\ +---+---+---+---+---+---+---+---+ | R | | B | Q | K | | | R | / | R | | B | Q | | R | K | | +---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+ King-side castling
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The knight moves by 'jumping' in an L-shaped pattern, two squares in any non-diagonal direction and then one square perpendicular. The knight is the only piece that may jump over other pieces to reach its destination.
Pawns move straight forward by one square (or two from their starting position). They capture diagonally forward. If a pawn reaches the 8th rank, it can be promoted to a queen or knight.
A pawn on the fifth rank can capture an opposing pawn that has just moved two spaces forward on its initial move as if it had moved only one space forward. This "en passant" move was added soon after the two-space initial pawn move to preserve the interaction of pawns. We need more info on "en passant." You can edit this page right now!
In tournament play and for quick chess, a chess clock is used; each player presses a button after every move and the clock keeps track of the time used. In correspondence chess, the moves are sent by mail and every player is given a set number of days per move.
Some rules of thumb for playing well are given on the Chess Strategy and Tactics page.
Lists of World Champions and famous players are available.
In May 1997, a computer (IBM's updated [Deep Blue]?) defeated the then reigning world champion Gary Kasparov in a match. IBM keeps a web site of the event at http://www.chess.ibm.com. While not an official world championship, the outcome of the match is often taken to mean that the strongest player in the world is a computer. Such a claim is open to strong debate, as there are other players whose playing style is recognised as more effective against other computer opponents, and it was impossible for Kasparov to prepare to play the machine as he would against a human opponent, as the computer's programming was adjusted between prior matches and the Kasparov match. Conversely, if the machine's programming was left fixed it would have been easy for Kasparov to figure out play lines where the machine is weaker and play to those weaknesses - thus, a truly fair match is very difficult to arrange. IBM retired Deep Blue after the match and it has not played since. However, given that computer hardware and chess algorithms have continued to improve since 1997 it seems likely that an equivalent effort would produce a computer that was more unambiguously stronger than the best human player.
It should be noted in all such speculation that computer chess is not of great academic interest to researchers in artificial intelligence. Chess-playing programs essentially explore huge numbers of potential future moves by both players and apply a relatively simple evaluation function to the positions that result. Such methods are useless for most other problems artificial intelligence researchers have tackled, and are believed to be very different from how human chess players select their moves. Minor variations to the rules would either make chess a trivially easy task for a computer to win, or conversely leave even elaborate computers easy pickings for amateur players. Therefore, the fact that the best efforts of chess masters and computer engineers are so finely balanced should probably be viewed as an amusing quirk of fate rather than the profound comment on thought that many in the past, including some of the early theorists on machine intelligence, thought it to be.
The world organization of chess players is the FIDE which organizes regular world chess championships. Recently, some players complained about arbitrary decisions by FIDE and left to start competing organizations.
Strong players are awarded the lifetime title "Grandmaster" by FIDE according to well-defined rules.
Chess originated from the Indian game Shatranj, about 1400 years ago. This game is related to xiang4 qi2 (象棋 Chinese Chess) in China, and Shogi in Japan. The game reached Russia via Mongolia, where it was played at the beginning of the 7th century. From India it migrated to Persia, and spread throughout the Islamic world after the muslim conquest of Persia. It was introduced into Spain by the Moors in the 10th century, where a famous games manual, the Libros de las Juegos, was written under the sponsorship of Alphonso X of Spain during the 13th century. It reached England in the 11th century, and evolved through various versions such as Courier.
By the end of the 15th century, the modern rules were adopted: pawns could move two squares on their first move, bishops could move diagonally arbitrary far (before, they jumped three squares diagonally) and the queen was allowed to move arbitrary far in every direction (before, she could only move one square diagonally). The game in Europe since that time has been almost the same as is played today. The current rules were completely finalized in the early 19th century.
The most popular piece design, the "Staunton set", was created by Nathaniel Cook in 1849, endorsed by the then leading player Staunton?, and officially adopted by FIDE in 1924.
The title "Grandmaster" was created by Russian Tsar Nicholas II who first awarded it after a tournament in Saint Petersburg which he had funded.
There are several variants of chess: suicide, where capturing moves are mandatory and the object is to lose all pieces, Fischer Random where the placement of the pieces on the 1st and 8th rank is randomized to disemphasize the value of opening theory, bughouse or tandem where two teams of two players face each other on two boards, the team players play different colors and the pieces captured by one partner can be placed on the board by the other instead of moving, and advanced chess where the players are allowed to consult a computer.
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