If a pawn is promoted to queen adjacent to the enemy king, is the king instantly in check?
1Check and promotion rules are independent.– user929304Aug 8, 2019 at 8:34
Simple rule for check: If you can capture my king on your next move, ignoring all pins, I'm in check.– ArlenAug 8, 2019 at 14:03
@arlen why "ignoring all pins" ? "If you can capture my king on your next move" would suffice, no? If one of my piece is pinned, you still can't move your king to one of its target location, right?– JeffreyAug 8, 2019 at 15:25
5If your pawn promotes adjacent to the enemy king, wouldn't the king already be in check?– Kilian FothAug 8, 2019 at 16:28
1@KilianFoth Not if the pawn captured on its promotion-move.– Rosie FAug 10, 2019 at 20:29
Per FIDE Chess Laws, rule 3.1, a piece is said to attack an opponent’s piece if the player’s piece can make a capture on that square (and in one more special case not relevant here). In full:
It is not permitted to move a piece to a square occupied by a piece of the same colour. If a piece moves to a square occupied by an opponent’s piece the latter is captured and removed from the chessboard as part of the same move. A piece is said to attack an opponent’s piece if the piece could make a capture on that square according to Articles 3.2 to 3.8.
A piece is considered to attack a square even if this piece is constrained from moving to that square because it would then leave or place the king of its own colour under attack.
Per rule 3.9, the king is in check when it is attacked by one or more of the opponent’s pieces.
Therefore, as soon as the move is completed, the king is in check.
If the pawn is adjacent to king before promoting, it's already in check. For example, pawn is on e7 and King is on d8, king is in check.
However, if pawn is 1 rank away from king and is promoted to queen, yes king is instantly in check. For example, pawn in on c7 and king is on e8, if c8Q, king is in check.
It is applicable for all the pieces not only for Queen.
21A pawn could end up adjacent to the enemy king after promoting if it captured a piece - that way the king wouldn't illegally be in check at the start of the move. King on e8, pawn on c7, cxd8=Q+.– D MAug 8, 2019 at 9:10
8If you count squares that are diagonally touching as adjacent (and why wouldn't you?) the king could be on the same rank as the pawn prior to the promotion. Aug 8, 2019 at 12:53
I initially thought that it isn't possible to promote a pawn on a back rank square that is adjacent to the king, as that would suggest that the opposing king was left in check on the previous turn. But remellion pointed out that a pawn could promote on a square adjacent to the king if it captures on its promoting move.
Either way, assuming no pieces are between the promoted pawn to queen and the opposing king, the white king would be in check on this next turn.
4You overlook a case: capturing with promotion. Black king on e8, white pawn on e7 takes something on d8, promoting. Aug 11, 2019 at 6:17
1I completely overlooked this haha. Good point Aug 11, 2019 at 20:12