This is the scenario: I pick up my Knight to capture my opponent's Bishop (touching the Bishop). I then realise my Knight was pinned to my King in the first place, so moving it would be illegal. However, I have already touched my opponent's Bishop with my Knight. Since I have touched my opponent's Bishop, would I have to capture the Bishop with another piece of mine (in this case my Queen can legally capture the Bishop instead), or am I allowed to just move any other piece entirely? Reference in FIDE Rules is Article 4.3.3 but it still seems it doesn't explain this scenario well enough.
2 Answers
Article 4.3.2 clarifies this -
4.3 Except as provided in Article 4.2 [j'adoube], if the player having the move touches on the chessboard,with the intention of moving or capturing:
4.3.2 one or more of his opponent’s pieces, he must capture the first piece touched that can be captured
In the scenario you describe you touch your knight and your opponent's bishop with the intention of capturing the bishop with your knight. Moving the knight is illegal hence you may not capture the bishop with the knight. However capturing the bishop with some other piece, your queen, is legal. Therefore you must capture the bishop with that piece.
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1In the lawbook I found, there is a section right after this which I think is much clearer. "[If a player deliberately touches...] one piece of each colour, he must capture the opponent’s piece with his piece or, if this is illegal, move or capture the first piece touched which can be moved or captured."– amalloyCommented Feb 15, 2019 at 22:59
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1@amalloy The reference you have given is for the FIDE Laws of Chess before 1st July 2014. Since then they have changed 3 times. The current version, valid from 1st January 2018, is here - fide.com/fide/handbook.html?id=208&view=article. That is the version the OP references and it is the one that should be used for current competitions.– Brian Towers ♦Commented Feb 15, 2019 at 23:35
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1Indeed. Then from that reference, it seems law 4.3.3 is the relevant one: 4.3.2 appears intended to apply to when you have only touched an opponent's piece, touching no piece of your own.– amalloyCommented Feb 16, 2019 at 0:16
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And what happens if there's nothing that could capture the bishop? Commented Feb 16, 2019 at 3:09
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1I believe that the conclusion here is correct but that the reasoning is faulty. It looks to me like the scenario described in the question is governed by article 4.3.3, not article 4.3.2, as I argue in my answer below; article 4.3.2 only applies in the scenario where the player has only touched his opponent's pieces, and none of his own color, and is therefore not relevant here. @amalloy got this right, and telling him to "brush up on his reading skills" in your comment above was unwarranted. Commented Apr 6, 2019 at 17:25
The relevant sections from https://www.fide.com/fide/handbook.html?id=208&view=article:
4.2.1Only the player having the move may adjust one or more pieces ...
4.2.2Any other physical contact with a piece, except for clearly accidental contact, shall be considered to be intent.
4.3Except as provided in Article 4.2, if the player having the move touches on the chessboard,with the intention of moving or capturing:
4.3.1one or more of his own pieces, he must move the first piece touched that can be moved
4.3.2one or more of his opponent’s pieces, he must capture the first piece touched that can be captured
4.3.3one or more pieces of each colour, he must capture the first touched opponent’s piece with his first touched piece or, if this is illegal, move or capture the first piece touched that can be moved or captured. If it is unclear whether the player’s own piece or his opponent’s was touched first, the player’s own piece shall be considered to have been touched before his opponent’s.
Article 4.2.2 establishes that any non-accidental contact shall be considered intent, so touching the opponent's bishop with your knight establishes intent to capture. At that stage, you've touched both your knight and your opponent's bishop - that is, you've touched "one or more pieces of each colour" - so article 4.3.3 dictates what happens next.
Let's break down article 4.3.3, then. It first says you must:
capture the first touched opponent’s piece with his first touched piece
(nope, you can't do that - it's an illegal move)
or, if this is illegal
(it is)
move or capture the first piece touched that can be moved or captured
Since your knight cannot be moved, the "first piece touched that can be moved or captured" is your opponent's bishop. Therefore you must capture it.