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Comment by JohnKemeny | Hacker News Reader

Well, if a piece is pinned it's illegal to move it.

Rule 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.

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Unlike en-passant and castling, pinning and discovered checks are consequences of lower-level rules.

At the "Is this move legal?" level, they don't need unique rules of its own if the lower-level rules are specified correctly.

3.9.2: no piece can be moved if that exposes or leaves its own king in check.

That's a consequence of not being allowed to put yourself in check (by any means).

The only way to put yourself in check is by moving.

The only action you can ever take in chess is moving.

You can resign, too.

You can put yourself in check by moving the king. That has nothing to do with pinning. Adding a rule for pinning is redundant.

It isn’t an added rule for pinning. It’s the only rule about putting yourself in check.

Did you mean putting your opponent in check? In chess, you are not allowed to put yourself in check.

You said “ That's a consequence of not being allowed to put yourself in check (by any means).” My point is that there are no other means.

I was replying to a comment quoting an official rule saying "no piece can be moved if that exposes or leaves its own king in check."

I was pointing out that that specific rule (read to mean that moving a piece pinned against a king is not allow) is not strictly necessary. Putting oneself in check is not allowed regardless of whether it's because you moved a piece that was pinned against your king or moved your king directly into the line of sight of an opponent's piece. These are the different "means."

As a sibling comment points out, "The only action you can ever take in chess is moving," so it's not particularly meaningful to say that the only way to put yourself in check is by moving.

And likewise, it's not particularly meaningful to say "That's a consequence of not being allowed to put yourself in check (by any means)."

The rule, "3.9.2: no piece can be moved if that exposes or leaves its own king in check." covers both the case of moving a pinned piece as well as moving the king into check, i.e. it covers all "means" of putting yourself into check.

That rule doesn't mean it's illegal to move a piece that's pinned. It just means that it's illegal to move it to a square that would expose the king. For example a pawn that's pinned vertically can still push forward, it just can't capture diagonally.

That's why treating colloquial concepts like "pinning" as though they are rules in and of themselves is not really precise or productive.

You can also pin a pawn to a queen, but the pawn can still legally move.

You're both right, depending on whether you mean relative pin vs absolute pin.

Pinning isn’t a rule, it’s just something that arises from other rules.

Also, pinning can happen with pieces that don’t include a king, which means you can just move out of the pin and expose whatever other piece.

It’s just a chess tactic, not a rule. It’s like saying a chess skewer is a rule too.

Well, a minor piece can be pinned in front of a queen. It would be legal to move the minor piece in that case, but you'd most likely lose the game if both sides' material were even before the move. Pinning is a tactic, not a rule.

The point is that, logically, the first part of that rule (“expose the king”) is implied by the second part (“leave that king”), so the first part is redundant. You could simplify the rule to:

No piece can be moved that will leave the king of the same color in check.

Pedantically I disagree, to leave something in a condition it must have been in that condition in the first place. We could have a game where you're allowed to place your king in check, but if it is in check at the start of your turn you must fix that.

While we're being pedantic though it's not a property of the piece that might be able to be moved that will place the king in check. It's a property of the move. For example we might imagine you have a rook between an enemy rook and your king. You can move the rook along the line between the enemy rook and the king, but not perpendicular to it.

The rule should be:

No move can be made where the moving players king is in check in the resulting position

You should submit it to FIDE.

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