Check

Help please.. say a white castle sits between white king and black queen.. blocking check on the white.. if black king moves into clean right of the white castle.. so that's check on black by the white castle

.But it can't move... is that legal.. my argument is as castle can't move it isn't check. Thanks

Black cannot move his king into check in any circumstance. The fact the white rook is pinned makes no difference. A pinned piece can still deliver check or checkmate. There is no requirement that piece is "able to move" to deliver check.

Your argument is actually illogical if you think about it. You are basically trying to say that the black king can move into check because the white rook cannot move and put his own (white) king into check! Your argument must surely apply equally to both players.

Makes sense. I thought that... but surprisingly difficult to find an answer anywhere in rules. I've been playing for decades and this only cropped up this week. Interesting. Always knew the king needs 'captured' I suppose I need to think of it like the pieces have say, a gun (clean line of sight to the king by say a opponents castle etc) rather than having to actually move onto the kings square and 'capture/grab' them. Cant move into check... under any circumstances then. Roger that. Thank you so much for your quick help. 

FIDE Rules Article 3.9.1 :

"The king is said to be 'in check' if it is attacked by one or more of the opponent's pieces, even if such pieces are constrained from moving to the square occupied by the king because they would then leave or place their own king in check."

Thanks. Just what I needed.