Chess Rule
En passant works only like this:
You can remember it by remembering this rule: if a pawn moved two spaces, it can be captured as if it had only moved 1 space.
Yes. dxc7.
No. The pawn making the capture always ends up on the sixth or third rank. http://www.chess.com/learn-how-to-play-chess.html#howtomove
"En Passant
The last rule about pawns is called “en passant,” which is French basically means “in passing”. If a pawn moves out two squares on its first move, and by doing so lands to the side of an opponent’s pawn (effectively jumping past the other pawn’s ability to capture it), that other pawn has the option of capturing the first pawn as it passes by. This special move must be done immediately after the first pawn has moved past, otherwise the option to capture it is no longer available. Click through the example below to better understand this odd, but important rule."
Yes. dxc7.
No. The pawn making the capture always ends up on the sixth or third rank. http://www.chess.com/learn-how-to-play-chess.html#howtomove
"En Passant
The last rule about pawns is called “en passant,” which is French basically means “in passing”. If a pawn moves out two squares on its first move, and by doing so lands to the side of an opponent’s pawn (effectively jumping past the other pawn’s ability to capture it), that other pawn has the option of capturing the first pawn as it passes by. This special move must be done immediately after the first pawn has moved past, otherwise the option to capture it is no longer available. Click through the example below to better understand this odd, but important rule."
I believe he was talking about the pawn on c7 that hadn't moved. That's a legal capture.
The first example the pawn cannot.
The idea is that the White pawn on e5 is attacking f6 and d6, so if the d or f pawn tried to move up 2 spaces to d5 or f5 it would essentially be passing over the squares where Whites d pawn is. Meaning White would have the option to capture if one of the pawns tried to pass over a square it is defending by moving 2 squares on its first move.
Yes. dxc7.
No. The pawn making the capture always ends up on the sixth or third rank. http://www.chess.com/learn-how-to-play-chess.html#howtomove
"En Passant
The last rule about pawns is called “en passant,” which is French basically means “in passing”. If a pawn moves out two squares on its first move, and by doing so lands to the side of an opponent’s pawn (effectively jumping past the other pawn’s ability to capture it), that other pawn has the option of capturing the first pawn as it passes by. This special move must be done immediately after the first pawn has moved past, otherwise the option to capture it is no longer available. Click through the example below to better understand this odd, but important rule."
I believe he was talking about the pawn on c7 that hadn't moved. That's a legal capture.
It is White's turn.
If it was Black's turn, it would be 4... cxd6.
can white pawn at d6 capture black pawn which moved from e7 to e5
No. The rule for en passant is explained above. The move you are asking about does not fit that rule and therefor d6 can not capture the pawn on e7 as it moves to e5.
The rule is often explained in an unnecessarily confusing way.
En passant -- in passing -- try to think of it as capturing by landing on the square the enemy pawn moves through. In the first diagram, the black pawn does not move through d7. In fact the only squares pawns move through are on the 6th rank for black and the 3rd rank for white. And so en passant only ever happens on these ranks.
Hope that helps.