A normal game of chess has three stages: the opening, the middlegame and the endgame. In the opening, a main goal is to bring out your pieces, because they do no good sitting on the first row; it is also important to try to control the center of the board right away. In the middlegame, a goal can be to attack the enemy king or to protect your own. In the endgame, one of the main goals is to try to promote a pawn. A pawn that reaches the far side of the board is exchanged for a new queen, rook, bishop or knight; many people think a pawn can only become a piece that was captured, but that is not true.

Players give pieces point values to help them think; a pawn is worth one point, a knight or bishop three, a rook five and a queen nine; the king has no point value, because it cannot be captured; these point values do not decide who wins a game. Scholar's mate is a four-move checkmate that attacks the weak f-pawn with a bishop and a queen; the f7 pawn is weak because only the king guards it; a Spanish priest named Ruy Lopez was one of the first chess masters, and he published his analysis of an opening in 1561.

Players also write down their moves. In algebraic notation each move is written with the letter of the piece and the square it moves to; the knight is N, because K is taken by the king, and the pawn has no letter. Under the touch-move rule, a player who touches a piece that can move must move that piece; a player can end a game by resigning, and a game can also be drawn if both players agree. Before chess clocks, one game could last up to 14 hours, and clocks came into competitive play in the 1800s. In the late 1400s, new rules made the queen by far the most powerful piece on the board, and the new game soon replaced the older, slower one.

Players have ratings. The Elo rating system was made by Arpad Elo, a physics professor and chess master; the U.S. Chess Federation adopted it in 1960 and FIDE in 1970. The grandmaster title is awarded by FIDE, the International Chess Federation, to a player with a 2500 FIDE classical rating who also earns norms. How many different chess games are possible? The Shannon number, about 10^120, is a rough estimate of how many move sequences are possible in chess. It comes from Claude Shannon's 1950 work; the longest master game on record was 269 moves, a draw between Ivan Nikolic and Goran Arsovic in Belgrade on 17 February 1989. It took 20 hours 15 minutes. In 1996 Kasparov played the computer Deep Blue in Philadelphia. Deep Blue won the first game, but Kasparov won the match, 4 to 2. In May 1997 Deep Blue won the rematch, 3.5 to 2.5.

Words to know

• middlegame: middle stage
• endgame: last stage
• notation: move writing
• Elo: rating system
• grandmaster: top title