Fifty move rule

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 consecutive moves. The intended reason for the rule is so that a player with no chance to win can't be obstinate and play on indefinitely harvcol|Hooper|Whyld|1992|, or seek a win purely due to an opponent's fatigue. All of the basic checkmates can be accomplished in well under fifty moves.

During part of the 20th century, with the discovery that certain endgames can only be won in more than fifty moves (without a capture or a pawn move) from certain positions (see History section), the rule was changed to include certain exceptions in which one hundred moves were allowed with particular material imbalances. However, in 1992 all such exceptions were abolished and the strict rule was reinstated.

Statement of rule

The relevant part of the official FIDE laws of chess is rule 9.3 [ [http://www.fide.com/info/handbook?id=124&view=article FIDE Laws of Chess] , October 2004] :

:"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."Naturally, if a player writes down his next move as under (a) above, it must not be a pawn move or a capture for a valid claim. Additionally, a claim doesn't have to be made at the first opportunity – it can be made any time when there were 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 under the rules though in practice, when a draw under the fifty-move rule can be claimed, one of the players is usually happy to claim it harvcol|Hooper|Whyld|1992|.

Games drawn under the fifty move rule before the endgame are rare. One example is the game Filipowicz - Smederevac, Polanica Zdroj 1966, [ [http://www.chessville.com/misc/History/Mad_Aussie_Trivia_Archive_12.htm Filipowicz - Smederevac (1966) game at Chessville - The Mad Aussie's Chess Trivia] ] which was drawn on move 70 without any captures having been made in the whole game and with the last pawn being moved on move 20.

Example

A draw by the fifty move rule could have been claimed after Black's 112^th move in a 1991 game between Anatoly Karpov and Garry Kasparov, but neither player claimed it. The last capture occurred on White's 63^rd move (and the last pawn move occurred before that). By FIDE rule 9.3 part (a), White could have written his 113^th 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 113^th move, either player could have claimed a draw on their turn to move, without having to write down their next move. Instead, the game continued a few more moves:: 113. Ng5 Ra6+: 114. Kf7 Rf6+: 115. ½-½ [ [http://www.chessgames.com/perl/chessgame?gid=1067317 Karpov-Kasparov ] ] If 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).

History

The rule has a long history, with Ruy López's 1561 text on chess including details of it.

At one time, it was believed that all winnable games could be won without exceeding the fifty-move rule. However, in the early twentieth century, some exceptions were found, including A. A. Troitsky's analysis of the two knights endgame as well as the endgame of rook and bishop vs. rook. The rules of chess were revised several times to admit exceptions to the fifty-move rule for certain specific situations.

Later investigations in the 1980s by computer science pioneer Ken Thompson using the Belle chess computer began discovering numerous endgames winnable in more than fifty moves. However, these often involved seemingly random moves that defied human comprehension or analysis, in situations that would hardly ever occur in real gameplay. [http://query.nytimes.com/gst/fullpage.html?res=9A0DE2D7173CF935A1575BC0A960948260&sec=&spon=&pagewanted=all] In addition to being considered aesthetically displeasing, it was simply far beyond the capabilities of even the best human players to find a sequence of hundreds of perfect moves in a row without any known strategy.

Accordingly, in 1992, a strict fifty-move rule was reinstated, without any exceptions.

Nevertheless, academic research in the field has continued. Exhaustive retrograde analysis using faster computers to build endgame tablebases has uncovered many more such endgames, often of previously unsuspected length. As of | 2008, the record is 517 moves (assuming best 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 queen and knight vs. rook and bishop and knight.

During the time periods when the fifty move rule admitted exceptions, there were a number of revisions. In 1928 FIDE enacted rules that 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, requiring that players agree to an extension for these positions before the first move is made harvcol|Whitaker|Hartleb|1960|. FIDE rules allowed seventy-five moves for the rook and bishop versus rook Harvcol|Müller|Lamprecht|2001|p=299.

At some point, the rule was changed to one hundred moves for such positions. Later more positions requiring more than fifty moves were found. FIDE included these endgames in the extended rule:
#queen versus two bishops
#queen versus two knights
#two bishops versus a knight
#two knights versus a pawn
#rook and bishop versus a rook, and
#a queen with a pawn on the seventh rank versus a queen. The one hundred move extension was in force for a short time, and it was changed to seventy-five moves in 1988 harvcol|Hooper|Whyld|1992|. In 1992 the rule was changed back to fifty moves for all positions. Early on, the fifty move rule applied to tournament games but not to match games Harvcol|Troitzky|2006|p=197.

Many of the longest games on record involve the rook and bishop versus rook endgame, when the rule for more moves was in effect. [ [http://www.xs4all.nl/~timkr/records/#Longest%20game Chess records © Tim Krabbé ] ] (See Pawnless chess endgames, Philidor position, and Cochrane Defense.)

ee also

* Rules of chess
* Threefold repetition
* Draw (chess)
* Endgame tablebase

Notes