In chess, the threefold repetition rule states that a player may claim a draw if the same position occurs three times during the game.
[1] Two positions are by definition "the same" if the same types of pieces occupy the same squares, the same player has the move, the remaining castling rights are the same and the possibility to capture en passant is the same.
The reasoning behind the rule is that if the position occurs three times, no real progress is being made and the game could hypothetically continue indefinitely.
The game is not automatically drawn if a position occurs for the third time – one of the players, on their turn, must claim the draw with the arbiter.
By contrast, the fivefold repetition rule requires the arbiter to intervene and declare the game drawn if the same position occurs five times, needing no claim by the players.
[8] The seventeenth[9] and eighteenth[10] game of the 1972 World Championship match in Reykjavik between Bobby Fischer and Boris Spassky were declared draws because of threefold repetition.
As noted above, one of the players must claim a draw by threefold repetition for the rule to be applied, otherwise the game continues.
In the fifth game[16] of the 1921 World Chess Championship match in Havana between José Raúl Capablanca and Emanuel Lasker, the same position occurred three times, but no draw was claimed.
The game[18] between Alexander Alekhine and world champion Emanuel Lasker in Moscow 1914 ended in a short draw.
[19] In the first game[20] between the two players in the St. Petersburg tournament 1914,[21] Alekhine, this time with the black pieces, after 21.Qd4 (see diagram), forced a draw by threefold repetition using a similar process.
[22] A famous draw for threefold repetition occurred in the fourth[24] game[25] between Lajos Portisch and Viktor Korchnoi in Belgrade in the Russia (USSR) vs. Rest of the World 1970 match.
In the game[28] between Garry Kasparov and Deep Blue in New York 1997, the game ended with a draw by agreement, because after 49...Kb4 (diagram), if White plays 50.g8=Q, Black can force perpetual check and claim a draw after 54.Kb1 by threefold repetition:[29] To detect fivefold repetitions can be challenging for the arbiter.
Under the fivefold repetition rule, however, the fifth occurrence of a position immediately terminates the game, and subsequent moves become irrelevant.
11.Nxd8 (diagram) Black can force perpetual check and so the draw by the following moves: 15...Bf2+ is only a twofold repetition, as White lost their castling right only after 12.Kd2.
The Berlin draw in the Ruy Lopez is one of the more commonly used lines, while Magnus Carlsen and Hikaru Nakamura finished out a dead rubber at the Magnus Carlsen Invitational with a variation of the Bongcloud Attack – Nakamura admitted that with both players secure in passage to the next round of the tournament he saw no value in attempting to force the win.
He claimed a draw by repetition after checking his scoresheet carefully, whereupon it was pointed out to him that in the first occurrence of position, Black's king had had the right to castle, whereas in the second and third it had not.
Tournament rules stipulated that a player be penalized with three minutes of their time for incorrect claims, which left Karpov's flag on the verge of falling.
(Miles should have readily accepted a draw in that position, but Karpov was close to losing the game because of time control.)
The first use of such a rule was in a tournament in London in 1883, but was stated vaguely: "... if a series of moves be repeated three times the opponent can claim a draw."
After 42...Qe3 (see diagram), the game continued: Under modern rules, Black could claim a draw by informing the arbiter of their intention to play 50...Kg7, producing the same position as had occurred after 42...Qe3 and 46...Kg7.