# What is the “En passant” rule in chess?

How useful is that rule and how many times we can use that in one game?

Under what conditions can the en passant rule be used?

How often does it come up and is it a good idea to use it?

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En Passant is when an opponent's pawn is two ranks away from your pawn row (either 4th or 5th rank depending on color), and you move your pawn two spaces forward with one move, so that is is next to his pawn. You are allowed to make your first move with a pawn two spaces, but the En Passant capture allows your opponent to capture you just as if you had moved one space. Note, that this capture is only allowed as the very next move. This prevents you from being able to sneak pawns by your opponent's pawns.

It's not only useful, but chess would be a completely different game without it, since everyone would have to be very concerned about moving a pawn to the 4th or 5th rank, knowing that a pawn could get past them. The main way you could change it so that the game wouldn't change radically is to disallow 2-space moves by pawns, but that is still a substantial change from the way's it been*, and would eliminate the majority of standard openings. A less tumultuous change would be to simply prohibit double movement in the cases where an en passant capture would be possible. This would have almost the same exact effect as the en passant rule, since it happens more often that the threat of an en passant capture is enough to make an opponent not move two spaces, and actual uses of the move are rare.

* unless you go back to the 15th century, when the ability to move pawns two spaces was added to the game.

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It's worth noting that if pawns were only allowed to move one space at any time, the en passant rule wouldn't be required, and chess would still be the same game (albeit slower). – ire_and_curses May 11 '11 at 17:29
@ire, both good points, I'll edit the answer. – Lance Roberts May 11 '11 at 17:33
Great answer. I think that this move must be used very seldom, since its primary value is as a sort of preventive threat. – Andrew Vandever May 11 '11 at 22:18
It's interesting to note that pawns used to be restricted to single space moves - and consequently there was no en passant rule: en.wikipedia.org/wiki/Pawn_%28chess%29#History – tttppp May 12 '11 at 7:08
@Andrew Vandever: It is rare, but definitely important, like promoting a pawn (queen isn't always the right answer). – Andy May 19 '11 at 15:25

En passant captures are allowed only against a pawn that has advanced two spaces on its first move. A unit that marched at "double time" like this would probably rest after half the journey, then resume its march to the destination. This is true when your pawn is on the "fifth" rank (e.g. you have a black pawn on d5), and an adjacent pawn has moved from say, d2 to d4.

So assume that this pawn marches one square to d3, 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. This capture is allowed only on the immediate following move.

In theory, you could have as many as eight en passant captures in one game (as proved by a commenter below; an earlier version of this post wrongly said "four"). But in practice, en passant captures are rare (once in many games) because the necessary pre-conditions don't occur often. And even when they do, the advantage of having advanced pawns entrenched on the fifth rank means that they aren't used to make captures without a very good reason. And if the defending pawn is not molested on the fourth rank by the fifth rank pawn at that time, it cannot be disturbed later on by the same pawn.

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This answer doesn't provide anything useful that the already old and accepted answer does; and how it makes sense thematically is not relevant to the rules question. – GendoIkari Jan 27 at 18:30
@GendoIkari: I believe that the last paragraph does add something over and above the accepted answer. Especially with the addition of a new first sentence and the moving of the new last sentence. – Tom Au Jan 27 at 18:35
"In theory, you could have as many as four en passant captures [...]" I think it is actually possible to have eight en passant captures in one game. – Rainbolt Jan 27 at 18:37
@Rainbolt: I added "by one side." If all eight of Black's pawns were on the fifth rank, none of White's would make it to the fourth. I'll grant you that Black could have four fifth rank captures, and then White could move four pawns to the fifth rank and make four captures of the remaining Black pawns. – Tom Au Jan 27 at 18:40
Here you go. Eight en passant captures, all made by white, all in one game. (Note: I stopped playing after the eight captures were made.) `1. b4 Nc6 2. b5 a5 3. bxa6 Ne5 4. a4 Ng6 5. a5 b5 6. axb6 Nh4 7. d4 Nf5 8. d5 c5 9. dxc6 Nh4 10. c4 Nf5 11. c5 d5 12. cxd6 Nh4 13. f4 Ng6 14. f5 e5 15. fxe6 Ne5 16. e4 Nc4 17. e5 f5 18. exf6 Na3 19. h4 Nc4 20. h5 g5 21. hxg6 Na3 22. g4 Nc4 23. g5 h5 24. gxh6 *` – Rainbolt Jan 27 at 18:48