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Threefold repetition requires that the same "potential for moves". For example, if a En Passant could be played in one position but not another, it does not count as the same position.

With respect to threefold repetition, would the positions be considered the same if:

  • In the first position, the king cannot castle because it is in check, pieces are blocking, or for some other reason, but it could castle otherwise.
  • In the second position, the king cannot castle because it has already moved.
8

According to the FIDE Laws of Chess:

9.2.2 Positions are considered the same if and only if the same player has the move, pieces of the same kind and colour occupy the same squares and the possible moves of all the pieces of both players are the same. Thus positions are not the same if:

9.2.2.1 at the start of the sequence a pawn could have been captured en passant
9.2.2.2 a king had castling rights with a rook that has not been moved, but forfeited these after moving. The castling rights are lost only after the king or rook is moved.

Hence the answer to

With respect to threefold repetition, would the positions be considered the same if:

In the first position, the king cannot castle because it is in check, pieces are blocking, or for some other reason, but it could castle otherwise

Although castling is temporarily prevented the king still has castling rights. They are not lost if castling is temporarily prevented by check or blocking pieces. They are only lost if the king or rook moves.

With regard to:

With respect to threefold repetition, would the positions be considered the same if:

In the second position, the king cannot castle because it has already moved.

The rules are clear. If the king has lost castling rights since the the first position then the positions are not the same and a draw cannot be claimed.

Does permanent loss of castling rights reset three fold repetition?

Yes. That's what the rule says.

  • 2
    The wording of 9.2.2 is a bit confusing. Given 9.2.2.1, my explanation is that when they write "possible moves", they mean "the set of all legal future sequences of moves", not "the set of all legal next plies". But that could have been written better. – Federico Poloni Sep 30 at 11:33
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    The key is though, what if the position is such that although the king still has castling rights, there is no possible series of legal moves for it to castle? Like if it is immediately forced to move because of the check in the current position. Then all future possible moves are exactly the same. – RemcoGerlich Sep 30 at 12:04
  • @Brian Towers Don’t forget that the rules also sort of imply. that you still have castling rights even if the rook on that side has been captured, as long so as it was on it’s home square (I think). – Rewan Demontay Sep 30 at 12:33
  • @RewanDemontay That was the subject of my question - chess.stackexchange.com/questions/25113/…. Conclusion: you may have the right but you can't actually make the move without the rook involved. – Brian Towers Sep 30 at 13:20
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    @RewanDemontay: The "rook has been captured without moving" subtlety cannot be relevant for the threefold-repetition rule, though -- it's trivially impossible for any situation to recur after a capture anyway, because the total number of pieces on the board will have decreased. – Henning Makholm Sep 30 at 19:38

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