History
The rule has a long history (Stiller 1996:153). The 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 for the rule to be applied could be made for only some specific endgames, which varied from one set of rules to another. In this case, the move count started when the request for implementing the rule was made (not 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 (Hooper & Whyld 1992:134).
At one time, it was believed that all winnable endgames could be won within fifty moves. However, in the early twentieth 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 fifty 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 (FIDE 1944:17–18). (The actual maximal number of moves needed is 59.) (Speelman, Tisdall & Wade 1993:382). In 1952 FIDE revised the law, allowing for one hundred 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 fifty moves to be discovered (which is what happened). These positions were understood to require more than fifty moves:
- rook and bishop versus a rook
- two knights versus a pawn safely blocked by a knight behind the Troitsky line
- rook and pawn on a2 versus a bishop on black squares and a pawn on a3, plus the equivalent positions in the other corners (Whitaker & Hartleb 1960). (In 1979 it was shown that this endgame actually can be won in just under fifty moves (Giddins 2012:184,186).)
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 (Harkness 1970:52). The 1975 and 1977 versions of the rules included the same wording (also not specifying the positions or the number of moves) (Morrison 1975:25), (Morrison 1978:21).
In 1984 the rule was modified and it became Article 10.9. Now one hundred moves were explicitly specified and the positions above were listed in the rule (Kazic, Keene & Lim 1985:24–25). (The language 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 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. In 1989 the rule (still Article 10.9) was changed to 75 moves, and the listed positions were:
- Rook and bishop versus rook
- Two knights versus a pawn (no mention of the Troitsky line)
- A queen and a pawn on the seventh rank versus a queen (see queen and pawn versus queen endgame)
- Queen versus two knights (see pawnless chess endgame#Queen versus two minor pieces)
- Queen versus two bishops
- Two bishops versus a knight (see pawnless chess endgame#Minor pieces only) (FIDE 1989:22–23).
The rule was changed to allow for fifty moves in all positions. Some sources say that the 1989 rule was in effect only a "year or so" or a "few years" (Speelman, Tisdall & Wade 1993:382), (Lutz 1999:130) but one source of the 1992 rules gives the pre-1984 wording: "... increased for certain positions if it was announced in advance" (Goichberg, Jarecki & Riddle 1993:312). By 2001 the rule was Article 9.3 and allowed fifty moves for all positions (Schiller 2003:27–28).
Research in the field of 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. As of 2008, the record is 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.
Many of the longest games on record involve the rook and bishop versus rook endgame, when the rule for more moves was in effect. (See pawnless chess endgame and rook and bishop versus rook endgame.)
Read more about this topic: Fifty-move Rule
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