Chess and drawing by threefold repetition

Chess is an ancient game with simple rules, so you might think the official written rules would have evolved to be very clear and concise, and to unambiguously cover all corner cases (at least as to which moves are legal, and how the outcome of the game is determined). But I’m not so sure.

I’ll consider the FIDE Laws of chess, the version effective 1 January 2018. They might be found at <http://www.fide.com/fide/handbook.html?id=208&view=article>.

A draw can be claimed if the same position occurs for the third time. So it is important to know exactly how to tell if two positions are “the same”. Yet the relevant rule is written in a way that, it seems to me, is less than completely clear.

Consider this position:

chess-drawrepetition-1

Assuming white has castling rights, is it possible for this position to be “the same” as some future position (i.e. some position that looks the same, but has different castling rights)? It’s easy to prove that white can never castle, because his only legal move is king to d2, which forfeits his castling rights. So, all the possible moves of all the pieces of both players, for the rest of the game, are the same regardless of white’s castling rights.

Here’s what the rulebook says:

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 […]

By my reading, Article 9.2.2 says yes, some future position can be “the same” as this one, even though castling rights will have changed.

It is strange how it refers to the possible moves of “both players”, even though it is only one player’s turn to move. I can only assume that is its way of saying that we must consider all the possible future moves of both players, for the rest of the game.

I chopped it off there, because anything in a “thus” section would, I assume, be non-critical clarifying information that can be derived from the first part. Continuing:

[…] 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.

I guess I was wrong. Article 9.2.2.2 contradicts what Article 9.2.2 just said. It says that two positions cannot be the same if castling rights are different.

I call foul. It’s not okay to write “X; thus Y” if Y does not follow from X. It would be okay if they changed the word “thus” to “furthermore”.

I have another issue with the threefold repetition rule, caused by some other rules that were recently added:

9.6 If one or both of the following occur(s) then the game is drawn:

9.6.1 the same position has appeared, as in 9.2.2 at least five times.

9.6.2 any series of at least 75 moves have been made by each player without the movement of any pawn and without any capture. […]

Can two positions be “the same” if in one, a mandatory draw could happen in two moves, but in the other, it would take three moves? In other words, is a move still a “possible move” if it could not actually happen because the game would have already ended due to a mandatory draw?

The intended answer is undoubtedly “yes”, because otherwise the threefold repetition rule would never apply, and the fivefold repetition rule would be recursive. But I think the rulebook should be clear about it.

If you asked me, I’d suggest editing the rules to be something like this:

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, the possible moves of all the pieces of the player who has the move are the same, and castling rights 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.

With castling rights explicitly included in 9.2.2, I don’t think we ever have to look further ahead than the moves that are immediately available to the player to move. So, the fivefold repetition rule and the 75-move rule are no longer a problem.

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