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Consider a player who is in check. Suppose they can make a move that would checkmate the opponent, but would not stop themselves from being in check. Would that be a legal move?

For example, in the position below, if Black plays ...Rf8, it will put the White king in checkmate, but the Black king will still be in check. Is this move legal?

[FEN "K7/8/2n5/1r6/8/8/3k3R/5r2 b - - 1 0"]
[StartFlipped "0"]

Note that this position is displayed from White’s point of view, even though it is Black’s move.

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    This is not putting white in checkmate.
    – TylerH
    Commented Mar 22, 2022 at 13:51
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    @TylerH It certainly looks it t me - why isn't it? What valid move does the white king have?
    – Steve Ives
    Commented Mar 23, 2022 at 9:38
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    @SteveIves Checkmate requires no escape from check. White can escape from check by taking Black's king and winning the game. QED, not checkmate. (To be clear, my comment above is intended as a bit of a frame challenge by highlighting that the language used is problematic and that's why OP has this confusion in the first place).
    – TylerH
    Commented Mar 23, 2022 at 15:22
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    I'm with @TylerH here. The situation you are trying to describe can't happen, because by definition the only way to avoid having your king captured on the next move is to escape check.
    – Carl Witthoft
    Commented Mar 24, 2022 at 11:42
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    @SteveIves "I could win if I could perform this illegal move" is not a useful/valid argument in determining the outcome of a Chess game.
    – TylerH
    Commented Apr 5, 2022 at 16:41

8 Answers 8

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For this kind of question, if you have doubts, just play chess with the goal of capturing the enemy king. The first player to capture the enemy king wins. This isn't the official rule, but it's effectively the same in almost all situations I'm aware of (it doesn't work for stalemate).

So after 1...Rf8+, White wins with 2. Rxd2. It doesn't matter that Black also threatens to capture White's king with 2...Rxa8, since White has already won.

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    Its better to clarify that a rule of chess force to get out of check, block the check or capture the piece giving check BEFORE anything else.
    – djnavas
    Commented Mar 22, 2022 at 9:56
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    It may be worth noting that the rules differ from a game that doesn't recognize check or checkmate, but players win by capturing the enemy king, in one important way: a player cannot be compelled to move his king into danger; if a player's king is not in immediate danger, but all moves would endanger it, the game is considered stalemated and scored as a draw rather than for a win by the player who could otherwise capture the king. This exception may seem subtle, but it greatly affects the range of endgames where checkmate can be forced.
    – supercat
    Commented Mar 22, 2022 at 15:51
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    @supercat That's already covered by the answer: "(It doesn't work for stalemate)"
    – amalloy
    Commented Mar 22, 2022 at 17:18
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    I've played many games where the goal really was capturing the king--when we were playing 5 minute games things--including threats to the king--sometimes get overlooked. Check had no special status, the game ended with a king capture. I never saw a game where the winner lost on time in a checkmate position but I did see a discovered check persist for IIRC 4 moves, neither side aware of it.
    – Loren Pechtel
    Commented Mar 23, 2022 at 1:48
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    I don't think it's that helpful to offer a simplified heuristic like this in response to a question about the rules. For instance, this heuristic would give you the wrong answer in the case of castling across check, or castling out of check.
    – Steve Bennett
    Commented Mar 23, 2022 at 12:05
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According the FIDE LAWS of CHESS:

3.9.2 No piece can be moved that will either expose the king of the same colour to check or leave that king in check.

So as @djnavas points out, if you are in check you have to do at least one of three things (without placing the king in another check) to get out of check and continue the game:

  • move the king out of check,
  • capture the piece checking you, or
  • block the check (by putting one of your pieces in between the king and the piece checking you).
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  • 14
    And of course, (4) resign.
    – Chuu
    Commented Mar 22, 2022 at 14:24
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    @Chuu 5) Mutually agree the game is a draw.
    – Patrick M
    Commented Mar 23, 2022 at 0:13
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    @PatrickM LOL! although I suppose it's possible that one might agree to a draw when they are currently checking their opponent in some circumstances.
    – Michael
    Commented Mar 23, 2022 at 17:30
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    @Michael Presumably, those circumstances include perpetual check, which seems like a likely outcome of this position.
    – Brian Drake
    Commented Mar 26, 2022 at 7:00
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    @Michael This is actually such a circumstance. White will keep checking and force black to either take the rook (causing stalemate) or repeat moves.
    – Comic Sans Seraphim
    Commented Mar 28, 2022 at 10:33
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No, this is not legal. The fact that the black king is still in check from the white rook overrides every other consideration. It doesn't matter that (were it not for the white rook) Black's move would be checkmate, it fails to get Black out of check, so it's not legal.

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    +1 This answer looks redundant to other answers, but this was not the case when it was posted. In fact, out of the answers currently visible, this was the first one to be posted.
    – Brian Drake
    Commented Mar 26, 2022 at 6:29
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No, this move (...Rf8#) is not legal. According to the FIDE Laws of Chess effective 1 January 2018:

3.10.2 A move is illegal when it fails to meet the relevant requirements of Articles 3.1 – 3.9

(This improves on pre-July 2014 rules by specifically defining “illegal” as well as “legal”.)

In this case, the relevant requirement is in Article 3.9.2:

No piece can be moved that will … leave [the king of the same colour] in check.

The consequence of this is that the checkmate does not count:

5.1.1 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 …

Instead, the game shall continue with a legal move (after reverting the illegal move):

7.5.1 An illegal move is completed once the player has pressed his clock. If during a game it is found that an illegal move has been completed, the position immediately before the irregularity shall be reinstated. … Article[] 4.3 … appl[ies] to the move replacing the illegal move. The game shall then continue from this reinstated position.

Article 4.3 is the so-called “touch-move” rule and, in this case, would require Black to play ...Rf2 (probably losing the rook on the next move).

Actually, the key point here is also covered in the introductory Article 1:

Leaving one’s own king under attack … is not allowed .

As an aside, ...Rb8# would also be checkmate, but would also be illegal. This rook has no legal moves, so “touch-move” would not be relevant here and Black would be able to make any legal move after the illegal move was reverted.

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    This is a good answer that actually refers to the rules.
    – Steve Bennett
    Commented Mar 23, 2022 at 12:09
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In the case of the 'primitive' form of chess, where leaving your king in check is not an 'illegal' move, your king would then be taken by an intelligent player, causing you to lose.

The fact that be you could take his king the next turn would not change this.

However, in 'modern' chess, having your king captured is illegal(The game ends at checkmate, where you have no way to get out of check). Since your king could be taken the next turn, you remain in check, and your only available move is one which gets you out of check, i.e., makes sure your king cannot be taken the next turn.

You might think that putting the other player in check(or checkmate) would make it so he could not take your king, but the same rule which binds him also binds you, so you also cannot place his king in check while your king is in check, unless you place his king in check(or checkmate) while getting your king out of check at the same time, which is not the case here.

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I mean, I'm no avid chess player, take what I say with a grain of salt, as I'm only trying to apply logic here. The point of check is that in the next turn, if you don't solve that situation, you lose. So, if you ignore check, and produce checkmate while you're still in check, it only means that YOUR next turn the enemy loses 100%. But you lose before that, as it's the enemy's turn and they take your king before proceeding with your play.

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No, that's not a legal move. When you are in check, you have to do anything that will stop you being in check, so any of:

  • Move king to a field not attackable by opponent pieces.
  • Move one of your non-king pieces in between to block the attack path. Not possible against the horse because it jumps.
  • Capture the opponent's piece that is threatening your king.

The real world analogy to your situation is that you are the leader and you are in the enemy sniper's scope and you know it. Your reaction is to move your men into position to kill the enemy leader. While your men are moving into position to surround the enemy leader, their sniper kills you. So even if hypothetically your men manage to later kill their leader, you still died first. You effectively committed suicide for a chance to take the enemy leader down with you.

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  • The first part of this answer mainly restates other answers, but in a poorly worded way. I do not know what “field” is supposed to mean. The piece on c6 is properly known as a “knight”, not a “horse” (FIDE Laws of Chess effective 1 January 2018, Article 2.2). I am not sure that the analogy is helpful: checks are common, especially among low-level players, and not necessarily indicative of the state of the game, while it is rare for leaders to be in mortal danger, and even more rare for the leaders on both sides to be in mortal danger simultaneously!
    – Brian Drake
    Commented Mar 26, 2022 at 6:14
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No. If you are in check, you have to get out of check, either by moving king or blocking check with other piece. Anything else is illegal.

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    I'm sorry but this doesn't add anything new that hasn't already been answered by someone else. And you also forgot that you can always capture the piece checking you.
    – Snostorp
    Commented Mar 23, 2022 at 10:44

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