Zugzwang
Zugzwang (German for "compulsion to move") is a situation found in chess and other games wherein one player is put at a disadvantage because they must make a move when they would prefer to pass and not move.
Description
The fact that the player is compelled to move means that his position will become significantly weaker. A player is said to be "in zugzwang" when any possible move will worsen his position.
The term is also used in combinatorial game theory, where it means that it directly changes the outcome of the game from a win to a loss, but the term is used less precisely in games such as chess.
Putting the opponent in zugzwang is a common way to help the superior side win a game, and in some cases, it is necessary in order to make the win possible.
The term "zugzwang" was used in German chess literature in 1858 or earlier, and the first known use of the term in English was by World Champion Emanuel Lasker in 1905.
The concept of zugzwang was known to players many centuries before the term was coined, appearing in an endgame study published in 1604 by Alessandro Salvio, one of the first writers on the game, and in shatranj studies dating back to the early 9th century, over 1000 years before the first known use of the term.
Positions with zugzwang occur fairly often in chess endgames. According to John Nunn, positions of reciprocal zugzwang are surprisingly important in the analysis of endgames.
Etymology
The word comes from German Zug "move" + Zwang "compulsion".
According to chess historian Edward Winter, the term had been in use in German in the 19th century.
Pages 353–358 of the September 1858 Deutsche Schachzeitung had an unsigned article 'Zugzwang, Zugwahl und Privilegien'. F. Amelung employed the terms Zugzwang, Tempozwang and Tempozugzwang on pages 257–259 of the September 1896 issue of the same magazine. When a perceived example of zugzwang occurred in the third game of the 1896–97 world championship match between Steinitz and Lasker, after 34...Rg8, the Deutsche Schachzeitung (December 1896, page 368) reported that 'White has died of zugzwang'.
The earliest known use of the term "zugzwang" in English was on page 166 of the February 1905 issue of Lasker's Chess Magazine.
The term did not become common in English-language chess sources until the 1930s, after the publication of the English translation of Nimzowitsch's My System in 1929.
History
The concept of zugzwang, if not the term, must have been known to players for many centuries. Zugzwang is required to win the elementary (and common) king and rook versus king endgame, and the king and rook (or differently-named pieces with the same powers) have been chess pieces since the earliest versions of the game.
Other than basic checkmates, the earliest use of zugzwang may be in this study by Zairab Katai, which was published sometime between 813 and 833, discussing shatranj.
The concept of zugzwang is also seen in the 1585 endgame study by Giulio Cesare Polerio, published in 1604 by Alessandro Salvio, one of the earliest writers on the game.
Joseph Bertin refers to zugzwang in The Noble Game of Chess (1735), wherein he documents 19 rules about chess play. His 18th rule is: "To play well the latter end of a game, you must calculate who has the move, on which the game always depends."
François-André Danican Philidor wrote in 1777 of the position at below right that after White plays 36.Kc3, Black "is obliged to move his rook from his king, which gives you an opportunity of taking his rook by a double check [sic], or making him mate".
Lasker explicitly cited a mirror image of this position (White: king on f3, queen on h4; Black: king on g1, rook on g2) as an example of zugzwang in Lasker's Manual of Chess.
The British master George Walker analyzed a similar position in the same endgame, giving a maneuver that resulted in the superior side reaching the initial position, but now with the inferior side on move and in zugzwang. Walker wrote of the superior side's decisive move: "throwing the move upon Black, in the initial position, and thereby winning".
Paul Morphy is credited with composing the position at right "while still a young boy". After 1.Ra6, Black is in zugzwang and must allow mate on the next move with 1...bxa6 2.b7# or 1...B (moves) 2.Rxa7#.
Zugzwang in chess
There are three types of chess positions:
- Each side would benefit if it were their turn to move
- Only one player would be at a disadvantage if it were their turn to move
- Both players would be at a disadvantage if it were their turn to move.
The great majority of positions are of the first type.
In chess literature, most writers call positions of the second type zugzwang, and the third type reciprocal zugzwang or mutual zugzwang.
Some writers call the second type a squeeze and the third type zugzwang.
Normally in chess, having tempo is desirable because the player who is to move has the advantage of being able to choose a move that improves their situation. Zugzwang typically occurs when "the player to move cannot do anything without making an important concession".
Zugzwang most often occurs in the endgame when the number of pieces, and so the number of possible moves, is reduced, and the exact move chosen is often critical. The first diagram at right shows the simplest possible example of zugzwang. If it is White's move, they must either stalemate Black with 1. Kc6 or abandon the pawn, allowing 1... Kxc7 with a draw. If it is Black's move, the only legal move is 1... Kb7, which allows White to win with 2. Kd7 followed by queening the pawn on the next move.
In many cases, the player having the move can put the other player in zugzwang by using triangulation. This often occurs in king and pawn endgames. Pieces other than the king can also triangulate to achieve zugzwang, such as in the Philidor position.
Zugzwang is a mainstay of chess compositions and occurs frequently in endgame studies.
See also
- Corresponding squares
- Forced move
- Game
- Game theory
- Key square
- Null-move heuristic
- Player (game)
- Seki
