When You Cannot Castle

Part of the Fundamentals section of Coddy's Chess journey. Lesson 33 of 41.

Castling is powerful, so the rules fence it in. Think of four gates, all of which must be open. Two of them close forever; two are only stuck for the moment.

White cannot castle kingside yet because the bishop still stands on f1

Gate one: the path must be empty. White's bishop still sleeps on f1, so no castling yet. Develop it and the gate opens.

Gate two is the permanent one: if your king has moved, you may never castle again, even if he tiptoes straight back to e1. Move a rook and you lose castling with that rook only. The board below looks perfectly ready, yet castling is illegal: this h-rook already went out and came home earlier in the game.

King and rook on their home squares but the castling right is already lost

King on e1, rook on h1, nothing between, and still no castling: the rook has moved before. Coming home does not restore the right.

Gate three: you cannot castle out of check. If your king is attacked, castling is not on the menu; answer the check the ordinary way first (move, block or capture) and maybe castle later.

Black rook on e5 checks the white king, so castling is illegal this move

The rook on e5 gives check. Castling is not one of the three answers to check; White must deal with the rook first.

Gate four: the king may not pass through or land on an attacked square. Every square he touches on the trip must be safe:

Black rook watching f1 stops White from castling through the attacked square

The black rook watches f1. To reach g1 the king would step through fire on f1: illegal. Chase the rook off first, then castle.

Two things that surprisingly do NOT stop you: your rook may be attacked, and on the queenside the square b1 may be attacked. The king never touches b1; only the rook passes it, and rooks are allowed to cross fire. The rules guard the king's path, nobody else's.

Try it yourself

Gate four, on the board: White is not in check, yet O-O is illegal here. Click the square on the king's path that the black rook attacks.