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Other than castling, the only "strange" move that chess pieces can ever make is en passant. It seems a little odd to me that someone thought that such a "different" move was so important to include in the legal moves. When and why did this come to be?

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    promotion is also strange (though without it the pawn would just get stuck on the far row). Indeed the pawn itself is very strange: besides promotion, there's the initial double move (which makes en passant an issue), and the fact that it moves one way and captures another and cannot move back. – Noam D. Elkies Feb 1 '18 at 17:37
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From Wikipedia:

Allowing the en passant capture is one of the last major rule changes in European chess that occurred between 1200 and 1600, together with the introduction of the two-square first move for pawns, castling, and the unlimited range for queens and bishops (Davidson 1949:14,16,57). Spanish master Ruy López de Segura gives the rule in his 1561 book Libro de la invencion liberal y arte del juego del axedrez (Golombek 1977:108). In most places the en passant rule was adopted as soon as the rule allowing the pawn to move two squares on its first move, but it was not universally accepted until the Italian rules were changed in 1880 (Hooper & Whyld 1992:124–25).

The motivation for en passant was to prevent the newly added two-square first move for pawns from allowing a pawn to evade capture by an enemy pawn. Specifically, the rule allows a pawn on a player's fifth rank the opportunity to capture the opponent's pawn on an adjacent file that advances two squares on its first move as though it had advanced only one square (Davidson 1949:16). Asian chess variants, because of their separation from European chess prior to that period, do not feature any of these moves.

  • Interesting, Ruy Lopez also introduced castling. I still wonder if it would really make a big difference to modern gameplay if en passant didn't exist. I suppose its introduction was too early for anyone to reasonably contest its virtue now, but I wonder if a rule like that will ever be introduced again. – Daniel Jun 12 '12 at 2:08
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    @Danielδ, I'm not so sure that Ruy Lopez introduced castling himself. There were many different formulations of castling floating about at different times and different places, but even more to the point, I doubt (though I'm certainly not sure) that he's responsible even for the castling move we know today. See my comment to xaisoft's answer at the question to which you linked. – ETD Jun 12 '12 at 2:31
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    Allowing the two-square pawn move but not en passant would make a huge difference. Passed pawns are extremely powerful, and you could turn an apparently unpassed pawn into a passed pawn by simply moving it two squares to get past the defending pawn. – Kef Schecter Apr 26 '18 at 17:32
  • Does anyone know what the limit was on bishops and queens? – caleb.breckon May 22 at 18:48
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The answers currently here don't fully explain the motivation for the rule. One answer quoted this Wikipedia passage:

The motivation for en passant was to prevent the newly added two-square first move for pawns from allowing a pawn to evade capture by an enemy pawn.

That is true, but it doesn't quite get to the heart of the matter: passed pawns are extremely powerful. A passed pawn is a pawn that can never be obstructed or captured by an opposing pawn. All else being equal, if one side has a passed pawn and the other doesn't, that side will usually win.

Consider this pawn structure:

8/p7/1p4p1/1PppPp2/8/2PP1P2/8/8 w - - 0 1

White has a passed pawn on the e-file because there are no black pawns that can stop it from reaching the eighth rank and queening. Black will have to rely on his other pieces (not pictured) to stop the pawn from queening, which means those pieces won't be available to do anything else.

Black's g-pawn, on the other hand, is not a passed pawn because white's f-pawn will eventually capture it if it tries to queen. That means white's pieces won't be tied down trying to stop the g-pawn.

Now look at black's a-pawn. It's not a passed pawn because it has to get past white's b-pawn before it can queen. However, if the a-pawn were allowed to advance two squares, and the en passant rule didn't exist, it would be a passed pawn because black could move it to a5 without being captured. But, since the en passant rule does exist, attempting this would be a horrendous mistake because white would capture the pawn en passant and suddenly white would have a passed pawn on the a-file.

So, in essence, the en passant rule allows you to advance your pawn to the fifth rank without fear that your opponent will simply bypass your pawn by moving two squares.

0

In a "real" war, if one army moves a unit adjacent to the enemy army, it is likely to provoke a return "fire" from the enemy army. In chess, this "fire" is expressed by capturing.

En passant is a compensation for a pawn being allowed to advance two spaces on its first move. A unit that marched at "double time" would probably rest after half the journey, then resume its march to the destination.

So assume that the pawn marches one square, rests, then tries to complete its march to the second square. But if there is an enemy pawn on the adjacent file, that pawn might start a "duel" with the marching pawn when it is resting. That would result in an en passant capture.

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    This answer makes no sense: if it did, then the same would hold for any pair of pieces that move next to each other - they would have to be allowed to capture despite it being illegal (say, a Bishop moving next to a Knight). En passant is a rule, andn as all rules, they are such for the sake of being such - no more, no less. – gented Jan 31 '18 at 15:32

protected by Phonon May 4 '18 at 14:22

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