Editing Perpetual check

{{Short description|Chess situation in which one player can force a draw by repeatedly checking}}

In the game of [[chess]], '''perpetual check''' is a situation in which one player can play an unending series of [[check (chess)|check]]s from which the defending player cannot escape. This typically arises when the player who is checking feels their position in the game is inferior, they cannot deliver [[checkmate]], and wish to {{chessgloss|forcing move|force}} a [[Draw (chess)|draw]].

A draw by perpetual check is no longer one of the [[rules of chess]], but will eventually allow a draw claim by either [[threefold repetition]] or the [[fifty-move rule]]. Players usually [[draw by agreement|agree to a draw]] long before that.<ref>{{Harvcol|Burgess|2000|p=478}}</ref>

Perpetual check can also occur in other [[chess variant|forms of chess]], although the rules relating to it might differ. For example, giving perpetual check is not allowed in [[shogi]] and [[xiangqi]], where doing so leads to an automatic loss for the giver.
{{AN chess|pos=toc}}

==Examples==
{{Chess diagram
|tright
|Example from Reinfeld
|  |  |  |  |  |  |kd|  
|  |  |  |  |  |  |pd|  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |kl|ql
|  |rd|  |  |  |  |  |  
|qd|  |  |bd|  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|White to move draws by perpetual check, starting with 1.Qe8+.
}}
In this diagram, Black is ahead a [[Rook (chess)|rook]], a [[bishop (chess)|bishop]], and a [[pawn (chess)|pawn]], which would normally be a decisive {{chessgloss|material}} advantage. But White, to move, can draw by perpetual check:
: '''1. Qe8+ Kh7'''
: '''2. Qh5+ Kg8'''
: '''3. Qe8+''' etc.<ref>{{Harvcol|Reinfeld|1958|pp=42–43}}</ref>
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. 
{{clear}}

===Unzicker vs. Averbakh===
{{Chess diagram
|tright
|Unzicker vs. Averbakh, 1952
|  |  |  |  |  |rd|kd|  
|  |rd|pl|  |  |  |pd|pd
|pd|  |  |  |  |nd|  |  
|  |  |  |pl|pd|  |  |  
|  |pl|  |  |pl|qd|  |  
|  |  |ql|  |  |  |  |pl
|pl|  |  |  |  |  |pl|  
|rl|  |  |  |rl|  |kl|  
|Perpetual check extricates Black from his difficulties.
}}
In the diagram, from [[Wolfgang Unzicker]]–[[Yuri Averbakh]], Stockholm [[Interzonal]] 1952,<ref>{{cite web |url=http://www.chessgames.com/perl/chessgame?gid=1153024 |title=Unzicker vs. Averbakh, Stockholm 1952 |website=[[Chessgames.com]] }}</ref> Black (on move) would soon be forced to give up one of his [[rook (chess)|rooks]] for White's c-[[pawn (chess)|pawn]] (to prevent it from [[promotion (chess)|promoting]] or to capture the promoted [[queen (chess)|queen]] after promotion). He can, however, exploit the weakness of White's {{chessgloss|kingside}} [[pawn structure]] with 
:'''27... Rxc7{{chesspunc|!}}'''
:'''28. Qxc7 Ng4!''' 
Threatening 29...Qh2{{chessAN|#}}. If 29.hxg4 then 29...Qf2+, salvaging a draw by threefold repetition with checks by moving the queen alternatively to f2 and h4.
{{clear}}

===Hamppe vs. Meitner===
{{Main|Immortal Draw}}
{{Chess diagram
|tright
|Hamppe vs. Meitner, 1872
|rd|  |bd|kd|  |  |  |rd
|  |  |pd|  |  |pd|pd|pd
|  |pd|kl|  |  |  |  |  
|pd|  |  |pd|pd|  |  |  
|  |  |  |  |  |  |  |  
|pl|  |  |  |  |  |  |  
|  |pl|pl|pl|  |  |pl|pl
|rl|  |bl|ql|  |  |nl|rl
|Down massive amounts of material, Black forces a draw by perpetual check.
}}
In a classic game [[Carl Hamppe]]–[[Philipp Meitner]], Vienna 1872,<ref>{{cite web |url=http://www.chessgames.com/perl/chessgame?gid=1250160 |title=Hamppe vs. Meitner, Vienna 1872 |website=[[Chessgames.com]] }}</ref> following a series of [[sacrifice (chess)|sacrifices]] Black forced the game to the position in the diagram, where he drew by a perpetual check: 
:'''16... Bb7+!'''
:'''17. Kb5''' 
If 17.Kxb7{{chesspunc|??}} Kd7 18.Qg4+ Kd6 followed by ...Rhb8#.
:'''17... Ba6+'''
:'''18. Kc6''' 
If 18.Ka4{{chesspunc|?}}, 18...Bc4 and 19...b5#.
:'''18... Bb7+ {{chessAN|½–½}}'''
{{clear}}

===Leko vs. Kramnik===
{{Chess diagram
|tright
|Leko vs. Kramnik, 2008
|rd|  |  |  |  |  |  |kd
|pd|pd|  |  |  |  |pd|pd
|  |  |pd|  |  |  |  |  
|  |  |  |  |  |ql|  |  
|  |  |  |  |  |  |  |pl
|  |  |qd|  |  |  |  |  
|  |  |pl|  |  |pl|pl|  
|  |kl|  |rl|  |  |  |rl
|Position after 24.Qxf5
}}
In the game [[Peter Leko]]–[[Vladimir Kramnik]], [[Corus chess tournament|Corus]] 2008, Black was able to obtain a draw because of perpetual check:<ref>{{cite web |url=http://www.chessgames.com/perl/chessgame?gid=1482384 |title=Leko vs. Kramnik, Wijk aan Zee 2008 |website=[[Chessgames.com]] }}</ref>
:'''24... Qb4+'''
:'''25. Ka2 Qa4+'''
:'''26. Kb2 Qb4+'''
:'''27. Kc1 Qa3+'''
:'''28. Kb1 ½–½'''
If 28.Kd2? Rd8+ 29.Ke2 Qe7+.
{{clear}}

===Fischer vs. Tal===
{| align="right" 
|-valign="top" 
|+
|
[[File:Bundesarchiv Bild 183-76052-0335, Schacholympiade, Tal (UdSSR) gegen Fischer (USA).jpg|thumb|right|upright=0.90|Fischer vs. Tal, 1960]]
|
{{Chess diagram  
|tright
|
|  |  |kd|  |  |  |  |  
|pd|pd|  |  |nd|  |  |ql
|  |  |  |  |qd|  |  |  
|pl|  |  |pd|  |  |  |  
|  |  |  |  |  |  |  |  
|pl|  |pd|  |  |  |  |  
|  |  |pl|  |  |pl|kl|pl
|  |  |  |  |  |rl|  |  
|Position after 21.Kxg2
}}
|}
A perpetual check saved a draw for [[Mikhail Tal]] in the game [[Bobby Fischer]]–Tal, Leipzig 1960,<ref>{{cite web |url=http://www.chessgames.com/perl/chessgame?gid=1008399 |title=Fischer vs. Tal, Leipzig 1960 |website=[[Chessgames.com]] }}</ref> played in the [[14th Chess Olympiad]], while Tal was [[World Chess Championship|World Champion]].  In this position Black played 
:{{pad}}'''21... Qg4+''' 
and the game was drawn.<ref>{{Harvcol|Evans|1970|p=53}}</ref>  (After 22.Kh1, then 22...Qf3+ 23.Kg1 Qg4+ forces perpetual check.)
{{clear}}

==Mutual perpetual check==
{{Chess diagram  
|tright
|[[John Roycroft|A. J. Roycroft]] (after [[Thomas Rayner Dawson|T. R. Dawson]]), 1976<ref>[https://pdb.dieschwalbe.de/search.jsp?expression=STIP%3D%27perpetual%27%0D%0A ''Die Schwalbe'']</ref>
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |rd|rd|  |  |  
|  |  |  |  |kd|  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |kl|  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |Nl|  |  |Nl|  |  
|Mutual discovered perpetual check with [[Nightrider (chess)|nightriders]]
}}
A mutual perpetual check is not possible using only the orthodox chess pieces, but it is possible using some [[fairy chess piece]]s. In the diagram, the pieces represented as inverted knights are [[nightrider (chess)|nightriders]]: 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:

:'''1. Ke3+ Kd5+'''
:'''2. Kd3+ Ke5+'''
:'''3. Ke3+ Kd5+'''

and so on. This is in fact a mutual perpetual ''discovered'' check.<ref>Tim Krabbé, [http://timkr.home.xs4all.nl/chess2/diary_6.htm Open chess diary] &ndash; see item 120</ref>
{{clear}}

{{Chess diagram  
|tright
|Noam Elkies, 1999
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|  |kd|  |  |  |  |  |  
|rd|  |  |  |kl|  |  |  
|  |  |  |nl|  |  |  |  
|  |  |  |  |  |  |  |  
|  |Nd|  |  |  |  |  |  
|bd|rl|  |  |  |  |bl|  
|Mutual discovered perpetual check with a camel
}}
[[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 a [[camel (chess)|camel]], a (1,3)-leaper. There could follow:
:'''1. Nb5+ Cc5+'''
:'''2. Nd4+ Cb2+'''
:'''3. Nb5+ Cc5+'''
and so on.<ref>Tim Krabbé, [http://timkr.home.xs4all.nl/chess2/diary_7.htm Open chess diary] &ndash; see item 125</ref>

[[Xiangqi]] and [[janggi]], due to the presence of their cannon pieces, can also have mutual perpetual check.
{{clear}}

==Perpetual pursuit==
{{Chess diagram
|tright
|S. Birnov, 1928
|  |  |  |  |  |  |bd|  
|  |  |kl|  |  |  |  |   
|  |  |  |  |  |  |  |  
|pl|  |pd|  |  |kd|  |  
|  |  |pl|  |  |  |  |pd
|  |  |pl|  |pl|  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |  |  |  
|White to play and draw
}}
Related to perpetual check is the ''perpetual 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.<ref>{{cite book |last1=Seirawan |first1=Yasser |author1-link=Yasser Seirawan |last2=Silman |first2=Jeremy |author2-link=Jeremy Silman |date=2003 |title=Winning Chess Tactics |location=London |publisher=Everyman Chess |pages=119–121 |isbn=1857443330}}</ref>

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:
:'''1. a6 Bxc4'''
A direct pawn race with 1...h3? fails, as White promotes first and covers the promotion square.
:'''2. e4+!'''
This pawn sacrifice forces Black to limit their bishop's scope along the long diagonal.
:'''2... Kxe4'''
Forced, as Black has to play ...Bd5 to stop the pawn.
:'''3. a7 Bd5'''
:'''4. c4!'''
Denying another square to the bishop, which must stay on the a8–h1 diagonal. This forces
:'''4... Ba8'''
And White can then begin the perpetual pursuit:
:'''5. Kb8 Bc6'''
:'''6. Kc7 Ba8'''
Black can make no progress.

{| align="right" 
|-valign="top" 
|+Bilek vs. Schüssler, 1978
|
{{col-begin|width=auto; float:right; clear:right}}
{{col-break}}
{{Chess diagram small
|tright
|
|rd|nd|  |qd|kd|bd|  |rd
|pd|  |  |  |nd|pd|pd|pd
|  |pd|pd|  |  |  |  |  
|  |  |  |nl|  |  |  |  
|  |  |bl|  |  |  |  |  
|  |  |  |  |  |pl|pl|  
|pl|pl|  |  |  |pl|  |pl
|rl|  |bl|ql|kl|  |  |rl
|White attempts to win the enemy queen...
}}
{{col-break}}
{{Chess diagram small
|tright
|
|rd|nd|  |ql|  |bd|  |rd
|pd|  |  |  |  |kd|  |pd
|  |pd|pd|  |  |pd|  |  
|  |  |  |nd|  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |pl|pl|  
|pl|pl|  |  |  |pl|  |pl
|rl|  |bl|  |kl|  |  |rl
|...but traps his own into a perpetual pursuit.
}}
{{col-end}}
|}
An example of perpetual pursuit being used in a game occurred in [[István Bilek]]–[[Harry Schüssler]], Poutiainen Memorial 1978. Bilek thought he could win the enemy queen with the combination
:'''10. Nf6+ gxf6'''
:'''11. Bxf7+ Kxf7'''
:'''12. Qxd8'''
However, Schüssler replied
:'''12... Nd5! ½–½'''
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.
{{clear}}

==History==
{{Chess diagram
|tright
|N.N. vs. Unknown, 1750
|rd|  |bd|  |  |  |  |  
|pd|pd|pd|  |  |bl|pd|kd
|  |  |  |pd|  |  |nl|pd
|  |  |  |  |pd|  |  |  
|  |  |  |  |pl|  |  |qd
|  |  |  |pl|  |nd|  |pl
|pl|pl|pl|  |  |bd|pl|  
|rl|  |bl|  |  |  |  |kl
|Final position after 15...Kh7
}}
The ''Oxford Encyclopedia of Chess Games, Volume 1 (1485–1866)'' includes all recorded games played up to 1800.<ref>{{Harvcol|Levy|O'Connell|1981|p=ix}}</ref> The earliest example of perpetual check contained in it is a game played by two unknown players in 1750:

:{{chessgloss|NN|N.N.}} vs. Unknown, 1750 <br />'''1. e4 e5 2. Nf3 Nc6 3. Bc4 Bc5 4. 0-0''' (the rules of [[castling]] not yet having been standardized in their current form, White moved his king to h1 and his rook to f1) '''4... Nf6 5. Nc3 Ng4 6. d3 0-0''' (Black moved his king to h8 and his rook to f8) '''7. Ng5 d6 8. h3 h6 9. Nxf7+ Rxf7 10. Bxf7 Qh4 11. Qf3 Nxf2+ 12. Rxf2 Bxf2 13. Nd5 Nd4 14. Ne7 Nxf3 15. Ng6+ Kh7 ½–½''' in light of 16.Nf8+ Kh8 17.Ng6+ etc.<ref>{{Harvcol|Levy|O'Connell|1981|p=9}}</ref>

The next examples of perpetual check in the book are two games, both ending in perpetual check, played in 1788 between Bowdler and [[François-André Danican Philidor|Philidor]], with Philidor giving [[chess handicap|odds]] of [[pawn and move]].<ref>{{Harvcol|Levy|O'Connell|1981|p=12}}</ref>

A draw by perpetual check used to be in the [[rules of chess]].<ref>{{Harvcol|Reinfeld|1954|p=175}}</ref><ref>{{Harvcol|Reinfeld|1958|pp=41–43}}</ref>  [[Howard Staunton]] gave it as one of six ways to draw a game in ''The Chess-Player's Handbook''.<ref>{{Harvcol|Staunton|1847|p=21}}</ref> It has since been removed because perpetual check will eventually allow a draw claim by either [[threefold repetition]] or the [[fifty-move rule]].  If a player demonstrates intent to perform perpetual check, the players usually [[Draw by agreement|agree to a draw]].<ref>{{Harvcol|Hooper|Whyld|1992|}}</ref>
{{clear}}

==See also==
*[[Desperado (chess)|Desperado]]
*[[Rules of chess]]
*[[Stalemate]]

==References==
{{Reflist}}

'''Bibliography'''
*{{citation
 |last=Burgess |first=Graham |author-link = Graham Burgess
 |title=The Mammoth Book of Chess 
 |publisher=Carroll & Graf 
 |year=2000 
 |edition = 2nd
 |isbn= 978-0-7867-0725-6}}
* {{Citation
 |last=Evans|first=Larry|author-link=Larry Evans (chess grandmaster)
 |title=Modern Chess Brilliancies
 |year=1970
 |publisher=Fireside
 |isbn= 0-671-22420-4}}
* {{Citation
 |last1=Hooper|first1=David|author-link1=David Vincent Hooper
 |last2=Whyld|first2=Kenneth|author-link2=Kenneth Whyld
 |title=[[The Oxford Companion to Chess]]
 |year=1992
 |edition=2nd
 |publisher=[[Oxford University Press]]
 |isbn= 0-19-866164-9}}
* {{Citation
 |last1=Levy|first1=David|author-link1=David Levy (chess player)
 |last2=O'Connell|first2=Kevin
 |title=Oxford Encyclopedia of Chess Games, Volume 1 (1485-1866)
 |year=1981
 |publisher=[[Oxford University Press]]
 |isbn= 0-19-217571-8}}
* {{Citation
 |last=Reinfeld|first=Fred|author-link=Fred Reinfeld
 |title=How To Be A Winner At Chess
 |year=1954
 |publisher=Fawcett
 |isbn= 0-449-91206-X}}
* {{Citation
 |last=Reinfeld|first=Fred <!-- |author-link=Fred Reinfeld -->
 |title=Chess in a Nutshell
 |year=1958
 |publisher=Pocket
 }}
* {{citation
 |last=Staunton | first=Howard | author-link=Howard Staunton
 |year=1847
 |title=The Chess-Player's Handbook
 |location=London | publisher=Henry G. Bohn}} (1985 Batsford reprint, {{ISBN|1-85958-005-X}})
<!-- Note to other editors:   **************
I've hidden this reference, since it seems not to be relevant.
**[[Project Gutenberg]] has the text of a different reprint from 1870 and 1910 at [https://www.gutenberg.org/ebooks/16377 The Blue Book of Chess by Howard Staunton and Various]
*********************** -->

==External links==
*[http://www.chessvariants.com/d.chess/eternal.html Perpetual Check] by [[Hans Bodlaender]], ''[[The Chess Variant Pages]]''

{{chess}}

[[Category:Rules of chess]]
[[Category:Chess terminology]]
[[Category:Chess tactics]]
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