En passant is relatively insignificant in chess games and in orthodox
chess problems. However, its action at a distance, its temporal dependency,
and its general weirdness make it a very important element in retrograde
En passant (like castling) is a conditional move, whose legality in
a position depends upon the history of the game. However, using retrograde
analysis it may be possible to deduce whether or not the last
move was the double step, and hence whether or not a given en passant
capture is legal. This is based on the fundamental principle for chess
problems, that any composition must show a legal position (i.e. one
that can could appear during a game as the result of a sequence of legal
Düna Zeitung, 1897
5+3. Mate in 2
By convention, with this kind of stipulation, we can assume that White
has the move (unless the position is only legal with Black to play).
Now by elimination, Black's last move can only have been 0 ...
g7-g5. Note in particular that 0 ... Kg7-h6 is impossible
since the White pawn on f6 could not have just moved to give check.
Therefore, in the diagram position, en passant capture is legal.
1. h5xg6ep Kh5 2. Rxh7# solves the problem.
That was an example of proven e.p. legality. Here is one where there
are two potential en passants, one of which is proved legal, and the
other is proved illegal.
Thomas R. Dawson
Falkirk Herald 17/06/1914
11+6. Mate in 2
All missing Black pieces have been captured by White pawns. So Black's
last move cannot have been 0 ... e7-e5 which would block the
Black king's bishop from leaving its home square. By elimination, Black's
last move must have been 0 ... c7-c5 and the queenside en passant
is legal. The solution is hence 1. bxc6ep followed by 2. c7#.
This composition has appeared, upside down and with colours reversed,
on chess problemists' Christmas cards!
The default convention is that, in a given position, if you
can't deduce whether a potential en passant is legal or not, then it
is not permitted. I.e., if uncertainly exists, you may assume
that the last move was not the relevant double pawn
The en passant convention was initially designed for orthodox chess
compositions, to remove what would otherwise be cooks. However, Retrograde
Analysts have taken the convention and used it as a basis for many compositions,
by deliberately exploiting situations where it's not possible to determine
by logic whether or not a given en passant is legal. For example:
1467 Die Schwalbe 31 02/1975
dedicated to F. Schützhold
11+6. White retracts 1 move, then #1
If White retracts 1. Rg8xNh8 then Black's last move cannot
be with the king because the prior check is impossible. This requires
careful counting of pawn captures - specifically considering the history
of the Black a pawn. The only other Black unit which might have moved
is the b pawn, which cannot have come from c6 (again, by counting pawn
captures). So the prior Black move was 0 ... b7-b5 and en passant
is legal, hence 1. cxb6ep#. Check that if White retracts anything
else, Black has at least one alternative last move, and by the en
passant convention, en passant capture by White would not be allowed.
En passant capture is the only way to give a double check without
moving either of the checking units. This makes it very interesting
to use as the key retro-move to reach a position. It's easy to overlook
this possibility when trying to solve a strange position. Of course,
if you retract a5xb6ep (say) then the prior move can only have been
1st/2nd Prize 4th Thematic Tourney
6+1. Last 6 single moves?
White just gave check with his Ba1. This can only have been a discovered
check but apparently no White piece could have been shielding the bK
from the wB. Here an en passant capture explains the check: the wPe6
The last move was -1. d5xe6ep+ ! and the prior moves
were -1 ... e7-e5 and -2. d4-d5+.
Now what was Black's move just before? It must have been played by
the bK, running from a double check. The only possible move leading
to an explainable double check involves another en passant capture.
Black just played -2 ... Ke6xPf6!!, and the moves prior
to that must have been -3. e5xf6ep+ f7-f5.
Note that again this problem uses the en passant rule heavily, but
not the en passant convention. In fact, the convention isn't applicable
to pure retrograde problems at all: it makes no statement to constrain
the past of the game. All it says is that if the past is unclear, you
are not permitted to play en passant going forwards.
This page has shown how a potential e.p. capture is
handled in isolation. But retro analysts delight in the strange
interactions possible with other conditional moves. For example,
there are some situations where one of several en passant captures
is legal but you can't tell which. And, there are situations where
en passant interacts with castling in various ways. See the
Castling and En-passant
capture in the Codex 2009 and the spectacular
Many thanks to Andrew Buchanan for providing this page!