On Mon, May 11, 2009 at 8:13 AM, David Wilson <davidwwilson@comcast.net>wrote:
On the other hand, I think there should be another slight modification to the rules of chess that I think is consistent.
The "en passant" rule says that if A's pawn moves two squares from the home rank, attacking B's pawn, and on the next play, B moves the attacked pawn one square forward to avoid capture, that A, on the next move, can capture B's pawn in the same rank as if A's pawn had moved only one square on the earlier move. But that same logic would apply to any piece that moved next to A's pawn in the same rank on the move following the A's two-square move. I argue that it should be possible to capture any piece en passant.
This would be a huge, not a small, change in the rules of chess, in some sense eliminating the power of pieces to attack at long range. A rook at a1 that moves to a6 is not taking 5 separate moves to a2, a3, a4, a5, a6. It is moving directly to a6. This rule also involves some complications to even state properly, to do with the fact that pieces other than pawns can not only move at long-range, they can capture at long-range. Suppose I make a capture, moving my rook from b2 to capture your piece at b5. If you now move a piece to a3 "capturing my rook en passant", is the piece at b5 put back on the board? Or is it captured by a phantom rook that never got to b5? Suppose I also have another rook at a5, and your king is at e5, pinning your knight that is at c5. May I move my knight from c5 to b3, capturing your rook en passant? This moves a pinned piece, temporarily opening a clear path from the rook on a5 to your king at e5, but the path is blocked again when I replace the captured piece at b5. Suppose my rook is at b2, and your king is at b5. Is your king in check, if you are able to capture the rook en passant at b3? Or in "capture the king" chess, do I lose the instant my king is captured, or can I continue to play if I make an en passant capture that uncaptures my king and returns it to the board? And what about knights? I don't see why they should be exceptions to this rule. Can a knight moving from b1 to c3 be captured at b2? c3? Either? Only the one that the mover of the knight specifies he is moving through? Suppose you move your rook from b2 to b5. Can I move my rook from b7 to b3, capturing your rook, or does the rook I am capturing on b5 block this move? Is the answer different if you made a capture on b5? Chess didn't start out with a feeling that "If you move a piece more than one square, the opponent should be able to capture it as it goes by" (a rule that tactical wargames often have in the form of "opportunity fire", but strategic wargames generally lack). But it did start out with the principle that "pawns only move one square at a time, and there's no way that my pawn on the c-file can get past your pawn on the d-file without you having the opportunity to capture it". This is especially important for pawns because the idea of pawns getting past other pawns is important because of promotion. So when the doublestep move was introduced, the en passant rule was added with it to keep this principle true. I could see an argument for generalizing the en passant rule by saying that when I move a pawn from c2 to c4, you may capture it en passant with *any* piece by moving that piece to c3 and removing the pawn on c3. Though even this runs into some of the logical difficulties above (for example, can this capture be made by a rook on c7?). The pawn's unique move, capture, and promotion are what makes chess what it is. The movement and capture rules lead to a pawn structure that is relatively static and long-lived, producing a framework around which strategy is built. And the promotion rule creates the possibility of material advantages that are nearly worthless in midgame, and decisive in endgame, increasing the possibility of positional sacrifice and dynamic equilibria. The pawn is what makes chess feel radically different from Shogi, Xiang Qi, and other abstract strategy games of maneuver and capture. Add in pieces like grasshoppers and mermaids, and start with the pieces swapped around, and you're still playing something that feels more or less like chess. Mess with the pawn move, and you're playing a different game. The en-passant rule is there to allow the doublestep move to speed things up, while messing with the pawn move as little as possible. -- Andy.Latto@pobox.com