In the game ofchess,perpetual check is a situation in which one player plays an unending series ofchecks from which the other player cannot escape. This typically arises when the player who is checking feels their position in the game is inferior, they cannot delivercheckmate, and wish toforce adraw.
A draw by perpetual check is no longer one of therules of chess, but will eventually allow a draw claim by eitherthreefold repetition or thefifty-move rule. Players usuallyagree to a draw long before that.[1]
Perpetual check can also occur in otherforms of chess, although the rules relating to it might differ. For example, giving perpetual check is not allowed inshogi andxiangqi, where doing so leads to an automatic loss for the giver.
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In this diagram, Black is ahead arook, abishop, and apawn, which would normally be a decisivematerial advantage. But White, to move, can draw by perpetual check:
The same position will soon repeat for the third time and White can claim a draw by threefold repetition; or the players will agree to a draw.
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In the diagram, fromWolfgang Unzicker–Yuri Averbakh, StockholmInterzonal 1952,[3] Black (on move) would soon be forced to give up one of hisrooks for White's c-pawn (to prevent it frompromoting or to capture the promotedqueen after promotion). He can, however, exploit the weakness of White'skingsidepawn structure with
Threatening 29...Qh2#. If 29.hxg4 then 29...Qf2+, salvaging a draw by threefold repetition with checks by moving the queen alternatively to f2 and h4.
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In a classic gameCarl Hamppe–Philipp Meitner, Vienna 1872,[4] following a series ofsacrifices Black forced the game to the position in the diagram, where he drew by a perpetual check:
If 17.Kxb7?? Kd7 18.Qg4+ Kd6 followed by ...Rhb8#.
If 18.Ka4?, 18...Bc4 and 19...b5#.
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In the gamePeter Leko–Vladimir Kramnik,Corus 2008, Black was able to obtain a draw because of perpetual check:[5]
If 28.Kd2? Rd8+ 29.Ke2 Qe7+.
_gegen_Fischer_(USA).jpg) |
Position after 21.Kxg2 | ||||||||||||||||||||||||||||||||||||||||||||
A perpetual check saved a draw forMikhail Tal in the gameBobby Fischer–Tal, Leipzig 1960,[6] played in the14th Chess Olympiad, while Tal wasWorld Champion. In this position Black played
and the game was drawn.[7] (After 22.Kh1, then 22...Qf3+ 23.Kg1 Qg4+ forces perpetual check.)
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A mutual perpetual check is not possible using only the orthodox chess pieces, but it is possible using somefairy chess pieces. In the diagram, the pieces represented as inverted knights arenightriders: they move any number of knight moves in a given direction until they are blocked by any piece along the path (that is, a nightrider is to a knight as a queen is to a king, ignoring the rules on check). There could follow:
and so on. This is in fact a mutual perpetualdiscovered check.[9]
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Noam Elkies devised in 1999 a mutual discovered perpetual check position that requires only one fairy piece. The piece represented by an inverted knight here is acamel, a (1,3)-leaper. There could follow:
and so on.[10]
Xiangqi andjanggi, due to the presence of their cannon pieces, can also have mutual perpetual check.
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Related to perpetual check is theperpetual pursuit, which differs in that the continually attacked piece is not the king. The result is similar, in that the opposing side's attack stalls because of the need to respond to the continuous threats.[11]
In the Birnov study illustrated, White's situation seems hopeless: they are down a piece and cannot stop Black's h-pawn, and their passed a-pawn can easily be stopped by Black's bishop. However, they can save themself by restricting the bishop's movement to set up a perpetual pursuit. They begin:
A direct pawn race with 1...h3? fails, as White promotes first and covers the promotion square.
This pawn sacrifice forces Black to limit their bishop's scope along the long diagonal.
Forced, as Black has to play ...Bd5 to stop the pawn.
Denying another square to the bishop, which must stay on the a8–h1 diagonal. This forces
And White can then begin the perpetual pursuit:
Black can make no progress.
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An example of perpetual pursuit being used in a game occurred inIstván Bilek–Harry Schüssler, Poutiainen Memorial 1978. Bilek thought he could win the enemy queen with the combination
However, Schüssler replied
and Bilek conceded the draw. His queen is now trapped, and with ...Bb4+ threatening to win it, he has nothing better than 13.0-0 Bg7 14.Qd6 Bf8 15.Qd8 Bg7 with another perpetual pursuit.
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TheOxford Encyclopedia of Chess Games, Volume 1 (1485–1866) includes all recorded games played up to 1800.[12] The earliest example of perpetual check contained in it is a game played by two unknown players in 1750:
The next examples of perpetual check in the book are two games, both ending in perpetual check, played in 1788 between Bowdler andPhilidor, with Philidor givingodds ofpawn and move.[14]
A draw by perpetual check used to be in therules of chess.[15][16]Howard Staunton gave it as one of six ways to draw a game inThe Chess-Player's Handbook.[17] It has since been removed because perpetual check will eventually allow a draw claim by eitherthreefold repetition or thefifty-move rule. If a player demonstrates intent to perform perpetual check, the players usuallyagree to a draw.[18]
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