Chess is a recreational and competitive game for two players. It is derived from Persian Shah ("the King"), an abbreviation of Shah-mat (Checkmate). Sometimes called Western Chess or International Chess to distinguish it from its predecessors and other chess variants, the current form of the game emerged in Southern Europe during the second half of the 15th century after evolving from similar, much older games of Indian and Persian origin .
Today, chess is one of the world's most popular games, played by millions of people worldwide in clubs, online, by correspondence, in tournaments and informally. Aspects of art and science are found in chess composition and theory. Chess is also advocated as a way of enhancing mental prowess.
The game is played on a square chequered chessboard with 64 squares. At the start, each player ("white" and "black") controls sixteen pieces: one king, one queen, two rooks, two knights, two bishops, and eight pawns. The object of the game is to checkmate the opponent's king, whereby the king is under immediate attack (in "check") and there is no way to remove it from attack on the next move. Theoreticians have developed extensive chess strategies and tactics since the game's inception.
The tradition of organized competitive chess started in the 16th century. The first official World Chess Champion, Wilhelm Steinitz, claimed his title in 1886; Viswanathan Anand is the current World Champion. There are also biennial world team events called Chess Olympiads. Since the 20th century, two international organizations, the World Chess Federation and the International Correspondence Chess Federation have organized and overseen the top chess competitions and international titles.
One of the goals of early computer scientists was to create a chess-playing machine, and today's chess is deeply influenced by the abilities of current chess programs. In 1997, a match between Garry Kasparov, then World Champion, and IBM's Deep Blue chess program proved for the first time that computers are able to beat even the strongest human players. The popularity of online chess coincided with the growth of the Internet.
Chess is played on a square board of eight rows (called ranks and numbered from 1 to 8) and eight columns (called files and labeled from a to h) of squares. The colors of the sixty-four squares alternate and are referred to as light squares and dark squares. The pieces are divided into two matching sets, by convention called White and Black. Each player, referred to by the color of his pieces, begins the game with sixteen pieces: one king, one queen, two rooks, two bishops, two knights and eight pawns. The chessboard is placed with a light square at each player's right on the nearest rank, and the pieces are set out on the two ranks closest to each player, as shown in the diagram. Each queen stands on a square of its own color.
The player who is chosen to be White makes the first move. The players then alternate moving one of their own pieces (with the exception of castling, when a rook and the king are moved simultaneously). Each type of piece has its own unique method of movement. Pieces are moved to either an unoccupied square, or one occupied by an opponent's piece. Except for captures en passant, an opponent's piece is captured and removed from play by moving a piece to the square that the enemy piece occupies. When a piece can be captured on the next move, it is said to be "threatened" or "under attack".
When a player's king is under immediate threat of capture, it is said to be in check. A player is not permitted to make any move that would place the player's own king in check. If a player's king is in check, the player's next move must take it out of check. If this is impossible, the player has been checkmated and loses the game.
Chess games do not have to end in checkmate either player may resign if the situation looks hopeless. Games also may end in a draw (tie). A draw can occur in several situations, including draw by agreement, stalemate, threefold repetition of a position, the fifty move rule, or a draw by impossibility of checkmate (usually because of insufficient material to checkmate).
Chess can be played with a time control. This involves assigning each player a set amount of time to make moves. If a player's time runs out before the game is completed, he loses on time. The timing ranges from up to seven hours for long games to shorter rapid chess games usually lasting 30 minutes or one hour. Even shorter is blitz chess, with a time control of three to fifteen minutes per player and bullet chess, in which the allotment is under three minutes.
Chess is played on a square board that is divided into sixty-four squares (8-by-8) of alternating color, which is very similar to that used in draughts (checkers). The chess boards used at chess tournaments have squares of approximately 50 to 65 mm (2.0 to 2.5 inches). The chess boards used at chess tournaments are usually green and buff, which is considered "easier on the eyes" than black and white, and because it is easier to distinguish occupied and empty squares when the board colors are different from the piece colors. No matter what the true color of the board (which come in a wide variety of colors), the (thirty-two) lighter colored squares are called "white", and the (thirty-two) darker colored squares are called "black". Upon the board move sixteen "white" and sixteen "black" pieces. The chess pieces used at chess tournaments are usually Staunton style shapes, and (unlike the board) often are black and white.
Each player has control of one of the two sets of colored pieces and are typically referred to by the nominal color of their respective pieces, i.e., White or Black. White moves first and, as in most board games, the players alternate moves. Play continues until a draw is declared, a player resigns, or a king is checkmated, as explained below.
Unlike Go, where the order of play is determined by the relative skills and handicaps of the players, the official chess rules do not include a procedure for determining who plays White. Instead, this decision is left open to tournament-specific rules or, in the case of non-competitive play, mutual agreement, in which case some kind of random choice is often employed.
The king can move exactly one square horizontally, vertically, or diagonally. At most once in every game, each king is allowed to make a special move, known as castling. Castling consists of moving the king two squares towards a rook, then placing the rook on the other side of the king, adjacent to it. Castling is only permissible if all of the following conditions hold:
1.The player must never have moved either the king or the rook involved in castling;
2.There must be no pieces between the king and the rook;
3.The king may not currently be in check, nor may the king pass through or end up in a square that is under attack by one or more enemy pieces.
4.The king and the rook must be on the same rank (to exclude castling with a promoted pawn).
In serious play, the king must be touched and moved first when castling; its move of more than one square makes clear that castling is intended.
The queen can move any number of vacant squares diagonally, horizontally, or vertically.
The bishop moves any number of vacant squares in any direction diagonally.
The knight moves to the nearest square not on the same rank, file, or diagonal. Equivalently, the knight moves two squares like the rook and then one square perpendicular to that. Its move is not blocked by other pieces, i.e. it leaps to the new square.
The rook moves any number of vacant squares vertically or horizontally. It also is moved while castling.
Pawns have the most complex rules of movement:
A pawn can move forward one square, if that square is unoccupied. If it has not yet moved, the pawn has the option of moving two squares forward provided both squares in front of the pawn are unoccupied. A pawn cannot move backward.
When such an initial two square advance is made that puts that pawn horizontally adjacent to an opponent's pawn, the opponent's pawn can capture that pawn "en passant" as if it moved forward only one square rather than two, but only on the immediately subsequent move.
Pawns are the only pieces that capture differently from how they move. They can capture an enemy piece on either of the two spaces adjacent to the space in front of them (i.e., the two squares diagonally in front of them), but cannot move to these spaces if they are vacant.
If a pawn advances all the way to its eighth rank, it is then promoted (converted) to a queen, rook, bishop, or knight of the same color, the choice being at the discretion of its player. In practice, the pawn is almost always promoted to a queen. If it converted to another piece, this is called "underpromotion".