1. en passant

Since the pawn double move was not intended to change gameplay (too much) but rather to speed the game up, en passant is a fairly obvious way that removes a pawns ability to double-move past one that would have been able to capture it if there were only single moves.

My question would be to ask why is this limited to pawns? Why not have every piece able to do this move? why not have it such that if a pawn moves from x2 to x4 (or x7 to x5) and another piece could have captured it on x3 (or x6), have that be a legal capture?

It may seem insignificant (and it kinda is I guess), but not always: imagine white has a pawn on a2 and the white king is ages away, and the black king is on b2 (and no other pieces exist). If it's white's move, the double-move allows it to evade capture by the king and eventually promote, but if the king could capture en passant as I suggest, it would be a draw.

Thoughts?

2. Originally Posted by Schu
Since the pawn double move was not intended to change gameplay (too much) but rather to speed the game up, en passant is a fairly obvious way that removes a pawns ability to double-move past one that would have been able to capture it if there were only single moves.

My question would be to ask why is this limited to pawns? Why not have every piece able to do this move? why not have it such that if a pawn moves from x2 to x4 (or x7 to x5) and another piece could have captured it on x3 (or x6), have that be a legal capture?

It may seem insignificant (and it kinda is I guess), but not always: imagine white has a pawn on a2 and the white king is ages away, and the black king is on b2 (and no other pieces exist). If it's white's move, the double-move allows it to evade capture by the king and eventually promote, but if the king could capture en passant as I suggest, it would be a draw.

Thoughts?

I have always thought this! I think it would occur quite a bit in openings but alot of them wouldn't be worth it. However it does open up a whole new range of sacrifices which would make the sicilian a whole lot more complex than it already is.

3. Originally Posted by Schu
My question would be to ask why is this limited to pawns? Why not have every piece able to do this move? why not have it such that if a pawn moves from x2 to x4 (or x7 to x5) and another piece could have captured it on x3 (or x6), have that be a legal capture?
I think the reason it applies only to pawns is that the rule is designed to stop pawns from blocking the position up too easily - it ensures that a pawn cannot move past another pawn without some opportunity for a capture one way or the other.

There is no reason to apply the same logic to pieces since if a pawn moves two squares to stand next to a piece, the piece will have other chances to capture it by virtue of its ability to move backwards.

The endgame case you mention (where a pawn uses its double jump to outpace a king) is an amusing one because the main purpose of letting pawns move two squares on their first move is to speed up the start of the game.

4. True, most pieces will be able to backtrack and stop a pawn that runs past them with the double move, but that's not to say that the same logic doesn't apply to pieces as pawns: the piece can backtrack, but the double-move could be used to force that piece to backtrack into defence, or there could be situations where that piece can't backtrack for tactical reasons. Either way, it still changes gameplay (though, granted, not to the same degree as it does with pawns).

One interesting case would be if there's a rook or queen on the same file as the pawn, and after the double move, if pieces could capture en passant, that rook or queen would have the option to capture the pawn either at its new location or one square back. I was going to say kings could have a similar choice too but I was wrong, for it to be in a position to do that, it would have to be in check already.

5. The poor pawns are weak enough, why handicap them further?