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Suppose that, in an amateur rapid play tournament (where supervision is inappropriate), the following position appears:

[fen "5K2/8/1q6/1N1k4/8/8/8/2R1R3 w - - 1 1"]

1. Re5+? Qc5+? {illegal} 2. Rxc5#

The players do not agree on the result of the game. White claims he won in virtue of the rule:

5.1.a.

The game is won by the player who has checkmated his opponent’s king. This immediately ends the game, provided that the move producing the checkmate position was in accordance with Article 3 and Articles 4.2 – 4.7.

Black claims the game is a draw in virtue of the rule:

Appendix A.4.d.

If the arbiter observes both kings are in check, or a pawn on the rank furthest from its starting position, he shall wait until the next move is completed. Then, if the illegal position is still on the board, he shall declare the game drawn.

Remark that the position after 2.Rxc5# is indeed illegal in virtue of the rule:

3.10.c.

A position is illegal when it cannot have been reached by any series of legal moves.

The referee remarks that there is a discussion about a game, moves to this table and listens to both claims. What is the correct decision?

A related question: suppose that the referee remarks the illegal position after 1.... Qc5+, and stays near this table, and assists to the move 2.Rxc5# What is the correct decision in this case?

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    I don't get why black just takes the rook as it's not concidered illegal as it doesn't check him again. In a match I wouldn't even think about moving my queen in this position.
    – Joshua Bakker
    Jan 14, 2016 at 9:11
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    @Joshua Bakker . My question about rules uses indeed a very implausible example (for a qualified chess player). It should be possible to find a better example of a legal move leading from an illegal position with with both kings in check to another illegal position.
    – Alexandre Aksenov
    Jan 16, 2016 at 19:15

4 Answers 4

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The mate stands and white wins. Although the position both before and after the mating move is illegal the mating move itself is legal therefore article 5.1.a is satisfied.

If an arbiter observes black playing 1...Qc5 then they declare the game lost for black for playing an illegal move. If they do not see the move but they observe the position after 1...Qc5 they will wait for white's move. Since white played 2.Rxc5 both kings are no longer in check hence article A.4.d does not trigger. In fact the purpose of the arbiter having to wait one move is to give the player a chance to correct the position. As it happens in this example the final position is still illegal but for a reason not covered by article A.4.d.

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    Thanks! The question is about understanding the last sentence of the article A.4.d. I understood it as "If any kind of illegal position is on the board..." According to you (and, I guess, you can be trusted), it is supposed to mean "If a position illegal for the same reason is on the board..." The question was partially motivated by the official French translation of this article.
    – Alexandre Aksenov
    Jan 16, 2016 at 19:34
  • @AlexandreAksenov Many thanks for that link! I am writing a Windows Phone "FIDE Laws of Chess" app (as much for my own benefit as anything else, there is no money in these things) and would like to include translations in the app where possible. FIDE deliberately don't copyright the Laws (according to one member of the FIDE Rules Commission I asked) but translations can be a different matter.
    – Brian Towers ♦
    Jan 20, 2016 at 17:38
  • @BrianTowers You are welcome! The linked document contains not only the rules of chess, but also the rules of pairings for the usual tournament systems, the procedure of becoming a national French arbiter and other things. Because of the additional content, it is updated more often, than the FIDE rules of chess. This document is copyrighted, as you can read here.
    – Alexandre Aksenov
    Jan 21, 2016 at 14:56
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Laws of Chess: For competitions starting on or after 1 July 2014

Article 7: Irregularities 7.1

If an irregularity occurs and the pieces have to be restored to a previous position, the arbiter shall use his best judgement to determine the times to be shown on the chessclock. This includes the right not to change the clock times. He shall also, if necessary, adjust the clock’s move-counter. 7.2

If during agame it is found that the initial position of the pieces was incorrect, the game shall be cancelled and a new game shall be played. If during a game it is found that the chessboard has been placed contrary to Article 2.1, the game shall continue but the position reached must be transferred to a correctly placed chessboard.

7.3

If a game has begun with colours reversed then it shall continue, unless the arbiter rules otherwise. 7.4

If a player displaces one or more pieces, he shall re-establish the correct position in his own time. If necessary, either the player or his opponent shall stop the chessclock and ask for the arbiter’s assistance. The arbiter may penalise the player who displaced the pieces. 7.5

If during a game it is found that an illegal move has been completed, the position immediately before the irregularity shall be reinstated. If the position immediately before the irregularity cannot be determined, the game shall continue from the last identifiable position prior to the irregularity. Articles 4.3 and 4.7 apply to the move replacing the illegal move. The game shall then continue from this reinstated position. If the player has moved a pawn to the furthest distant rank, pressed the clock, but not replaced the pawn with a new piece, the move is illegal. The pawn shall be replaced by a queen of the same colour as the pawn. After the action taken under Article 7.5.a, for the first completed illegal move by a player the arbiter shall give two minutes extra time to his opponent; for the second completed illegal move by the same player the arbiter shall declare the game lost by this player. However, the game is drawn if the position is such that the opponent cannot checkmate the player’s king by any possible series of legal moves.

7.6

If, during a game, it is found that any piece has been displaced from its correct square the position before the irregularity shall be reinstated. If the position immediately before the irregularity cannot be determined, the game shall continue from the last identifiable position prior to the irregularity. The game shall then continue from this reinstated position.

So I think, game returns to last position where no illegal move committed. 5.1.a is not applicable here, because 3.10.c violated, and satisfying Article 3 is a prerequisite for 5.1.a.

3.10.c

A position is illegal when it cannot have been reached by any series of legal moves.

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    5.1.a says "provided that the move producing the checkmate position was in accordance with Article 3 and Articles 4.2 – 4.7." 3.10.c says " A position is illegal when it cannot have been reached by any series of legal moves."
    – ferit
    Jan 9, 2016 at 0:55
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    5.1.a only applicable when there is no violation of 3, 4.2, and 4.7. And this game violates 3.10.c
    – ferit
    Jan 9, 2016 at 0:57
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    5.1.a says "provided that the move producing the checkmate position was in accordance with Article 3 and Articles 4.2 – 4.7". If the move is legal, then 5.1.a say the checkmate end the game.
    – limits
    Jan 9, 2016 at 2:50
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    Ok sure. But the move does not violate 3.10.c because it is about the position. And 7.5 does not apply because it says "is during a game", and the game is over. This was the response given by arbiter Geurt Gijssen to a similar question. The situation was that player A had made an illegal move. Player B did not point out that it was illegal, but chose to give mate in 1 (with a legal move) instead, so the game was over and player B won.
    – limits
    Jan 9, 2016 at 3:07
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    How can you return to a previous position in a rapid game? The rule 7.5.a , which you cite, only applies to long time control. On the other hand, for rapid play, it is stated in Appendix A.4.b , that "Once the opponent has made his next move, an illegal move cannot be corrected unless this is agreed by the players without intervention of the arbiter".
    – Alexandre Aksenov
    Jan 10, 2016 at 20:58
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IA Petr Harasimovic's opinion notwithstanding the game is drawn. Winning the game in an illegal position is a nonsense (barring serious misconduct or a ringing mobile phone). The problem is that the English (authoratative) version of the rules is ambiguously worded -

Then, if the illegal position is still on the board, he shall declare the game drawn.

Thank you, @AlexandreAksenov, for the link to the authorized French translation of the rules. They remove the ambiguity with a slight mistranslation, which I suspect may be deliberate -

si la position sur l’échiquier est toujours illégale, il déclarera la partie nulle

which translates back into English as "If the position on the board remains illegal, he shall declare the game drawn."

The British Chess Arbiters' Association has produced a version of the rules consisting of the FIDE rules verbatim with their own added comments to clarify points like these. Here is the relevant part of their clarification for A4.d:

Consider the following situations: ... (b) The arbiter arrives at the board. One king is already in check. The player completes a move checking the other king. The arbiter must wait until the next move is completed. If the position is still illegal he will declare the game drawn.

(My italics) This is eerily similar to the French. Perhaps no coincidence that the CAA has a French version (along with German and Russian) which looks like it was taken from the French Chess association website.

For completeness sake it is probably worth noting that the FIDE Arbiters' Association also has its own handbook! It has no clarifying comments for A4.d.

It also worth stressing that the FAA, CAA handbooks and the various translations by the different federations remain subservient to the original FIDE Laws of Chess as published on the FIDE website. The same applies to my opinions on A4.d expressed here and to the conflicting opinions of IA Petr Harasimovic. Nevertheless I suspect that the vast majority of FIDE arbiters would declare the game in question drawn.

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  • Challenge: find a single move that puts both kings in check.
    – Joshua
    Dec 18, 2017 at 18:23
  • @Joshua: White king on a1; rook on a2. Black bishop on c3; king on a6. Both kings would be in check, but if the rook were at b2, nobody would be in check. Likewise if the bishop were at a5.
    – supercat
    Jan 1, 2020 at 22:32
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In my personal opinion, the answers which follow from rules seem to be: White wins in the first case (by checkmate), draw in the second case (the situation of Appendix A.4.d happened before checkmate). Although, this seems a bit illogical since the only difference between the two situations is the time when the referee was present near the table.

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  • If players lie about the position, then it gets complicated, you are right about it. But these players don't get tolerated by community and get marked over time.
    – ferit
    Jan 10, 2016 at 23:13
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    The referee is supposed to follow the official rules, otherwise they are exposed to appeals from the coaches of the players. The reasons behind the FIDE rules constitute a different topic.
    – Alexandre Aksenov
    Jan 12, 2016 at 11:33
  • The players might claim that they forgot the previous moves, without explicitly lying. They might say (for instance) that they forgot whether the white rook was on c1 or on c2 before capturing the queen. Then, there is a big difference between returning to one or the other possible previous position.
    – Alexandre Aksenov
    Jan 12, 2016 at 11:37

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