The fifty-move rule in chess states that a player can claim a draw if no capture has been made and no pawn has been moved in the last fifty moves (for this purpose a "move" consists of a player completing his turn followed by his opponent completing his turn). The purpose of this rule is to prevent a player with no chance of winning from obstinately continuing to play indefinitely, or seeking to win purely by tiring the opponent out.
All of the basic checkmates can be accomplished in well under 50 moves. However in the 20th century it was discovered that certain endgame positions are winnable but require more than 50 moves (without a capture or a pawn move). The rule was therefore changed to allow certain exceptions in which 100 moves were allowed with particular material combinations. However, more and more such winnable positions were later discovered, and in 1992 FIDE abolished all such exceptions and reinstated the strict 50-move rule.
The relevant part of the official FIDE laws of chess is rule 9.3:
The game is drawn, upon a correct claim by the player having the move, if
- (a) he writes on his scoresheet, and declares to the arbiter his intention to make a move which shall result in the last 50 moves having been made by each player without the movement of any pawn and without the capture of any piece, or
- (b) the last 50 consecutive moves have been made by each player without the movement of any pawn and without the capture of any piece.
A claim does not have to be made at the first opportunity - it can be made any time when there have been no captures or pawn moves in the last fifty moves.
A game is not automatically declared a draw under the fifty-move rule - the draw must be claimed by a player on his turn to move. Therefore a game can continue beyond a point where a draw could be claimed under the rule. Theoretically, a game could continue indefinitely this way, but in practice, when a draw under the fifty-move rule can be claimed, one of the players is usually happy to claim it (Hooper & Whyld 1992:134). In 2014 FIDE amended the rules to eliminate the possibility that a game could continue without end. Rule 9.6b states that if 75 consecutive moves have been made without movement of any pawn or any capture, the game is drawn unless the last move was checkmate.
Games drawn under the fifty-move rule before the endgame are rare. One example is the game Filipowicz versus Smederevac, Polanica Zdrój 1966, which was drawn on move 70 without any captures having been made in the whole game and with the last pawn having been moved on move 20.
|Timman vs. Lutz, 1995|
In this 1995 game between Jan Timman and Christopher Lutz, an endgame with a rook and bishop versus a rook occurred. White is striving for the winning Philidor position while Black is employing the drawing Cochrane Defense and the "second-rank defense" (see rook and bishop versus rook endgame). Black was defending well in the difficult defense and could have claimed a draw on the 119th move. Lutz notes that he claimed a draw on move 121, ironically when making a move that gets into a losing position (Lutz 1999:129-32).
|Karpov vs. Kasparov, Tilburg, 1991|
A draw by the fifty-move rule could have been claimed after Black's 112th move in a 1991 game between Anatoly Karpov and Garry Kasparov, but neither player claimed it. The last capture occurred on White's 63rd move (and the last pawn move occurred before that). By FIDE rule 9.3 part (a), White could have written his 113th move (which wouldn't have been a capture or pawn move) on his scoresheet and claimed a draw. By FIDE rule 9.3 part (b), after White's 113th move, either player could have claimed a draw on his turn to move, without having to write down his next move. Instead, the game continued a few more moves:
The players agreed to a draw at this point because after 115. Kxf6 the position is a stalemate. If 115. Ke8 Rxf5 116. Nxf5, and the position is clearly drawn because the two knights cannot force checkmate (see two knights endgame).
|Lputian vs. Haroutjunian, 2001|
An unusual event occurred in a game in the 2001 Armenian Championship between Smbat Lputian (who won the championship) and Gevorg Haroutjunian. The last pawn move was on White's 86th move and no captures occurred after it. (The game was a theoretical draw from before here until Black's 141st move.) Black could have claimed a draw after White's 136th move (or at any of the subsequent moves). Instead, the game continued and Black resigned on his 142nd move - even though the right to claim a draw was still in effect.
The rule has a long history (Stiller 1996:153). The purpose of the rule is to prevent someone from playing on indefinitely in a position that cannot be won. A precursor to chess, Shatranj, had a seventy-move rule. The fifty-move rule was introduced into chess by Ruy López in his 1561 book. Pietro Carrera (1573-1647) thought that twenty-four moves was the right number but Bourdonnais (1795-1840) argued for sixty moves (Hooper & Whyld 1992:134).
By 1800 a claim under the rule could be made only in certain specified types of endgame, which varied from one set of rules to another. The move count started when the request to implement the rule was made (instead of going back to the last capture or pawn move) and a capture or a pawn move did not reset the count. The rules used at the 1883 London tournament reset the count if there was a capture or pawn move, but still started the count when the claim to apply the rule was made instead of going back to the last capture or pawn move.
At one time, it was believed that all winnable endgames could be won within fifty moves. However, in the early 20th century, some exceptions were found, including A. A. Troitsky's (1866-1942) analysis of the two knights endgame as well as the endgame of a rook and bishop versus a rook. The rules of chess were revised several times to admit exceptions to the fifty-move rule for certain specific situations. Early on, the fifty-move rule applied to tournament games but not to match games (Troitzky 2006:197).
During the time periods when the fifty-move rule admitted exceptions, there were a number of revisions. In 1928 FIDE enacted rules that if an endgame theoretically requires more than 50 moves to force checkmate, twice that number of moves were allowed. For instance, in the rook and bishop versus rook endgame, 132 moves were allowed, since it was twice the 66 moves that were thought to be required at that time. (The actual maximal number of moves needed is 59.) In 1952 FIDE revised the law, allowing for 100 moves in such positions but requiring that players agree to an extension for these positions before the first move is made. This was still in effect in 1960. The positions were not specified in the rules, to allow for the possibility of more positions requiring more than 50 moves to be discovered (which is what happened). The following positions were understood to require more than 50 moves:
Article 12.4 of the 1965 FIDE rules states:
The number of moves can be increased for certain positions, provided that this increase in number and these positions have been clearly established before the commencement of the game.
Harkness notes that "Some of these unusual positions have been established and accepted by FIDE", including two knights versus a pawn. The 1975 and 1977 versions of the rules included the same wording (not specifying the positions or the number of moves) .
In 1984 the rule was modified and it became Article 10.9. Now 100 moves were explicitly specified and the positions above were listed in the rule. (The wording about the positions and number of moves having to be specified in advance of the game was dropped.) Ken Thompson's investigations in the 1980s using the Belle chess computer discovered numerous endgames winnable in more than 50 moves. However, these often involved seemingly random moves that defied human comprehension or analysis, in situations that would hardly ever occur in real gameplay. In 1989 the rule (still Article 10.9) was changed to 75 moves, and the listed positions were:
The rule was then changed to allow just 50 moves in all positions. Some sources say that the 1989 rule was in effect for only a "year or so" or a "few years", but one source of the 1992 rules gives the pre-1984 wording: "... increased for certain positions if it was announced in advance". By 2001 the rule was Article 9.3 and allowed 50 moves for all positions.
Research into how many moves are required to win certain endgames has continued. Exhaustive retrograde analysis using faster computers to build endgame tablebases has uncovered many more such endgames, often of previously unsuspected length. In 2008, the record was 517 moves (assuming optimal play by both sides) to make a piece capture or exchange that achieves a simpler and more obviously winnable sub-endgame, for a particular position involving a queen and knight versus a rook, bishop, and knight. In 2013, this record was improved to 545 moves.