There are four important rules that govern Castling:
Rule #1: The King and Rook may not have moved from their starting
squares. In this board set-up, White cannot Castle to either side,
because both Rooks have moved from their starting squares. Even if
one of the Rooks moves back, White still cannot Castle.
Rule #2: All of the spaces between the Rook and the King must be
unoccupied. In this diagram, White cannot Castle Kingside because
the Knight is in the way. But he can Castle Queenside, because all of
the spaces between the King and the Rook are empty.
Rule #3: The King cannot be in Check. On this board set-up, it would
appear that White can Castle Kingside, because neither the King nor
Rook has moved from its starting square, and the spaces between the
Rook and King are empty. However, the White King is currently in
Check from the Black Bishop on b4, so he cannot Castle.
Rule #4: The squares that the King passes over cannot be under
attack, and since you can never move your King into Check, the
square to which it's moving can't be under attack either. On this
diagram, the spaces between the King and Rook on the Queenside
are open. However, two of the squares are under attack. The d1
square is under attack from the Black Bishop on g4, so the White King
cannot pass over it. And the c1 square is under attack from the Rook
on c8, so the King cannot land on it.
Again, the four rules governing Castling are:
1) The King and Rook may not have moved from their starting
squares;
2) All spaces between the King and Rook must be empty;
3) The King cannot be in Check; and
4) The squares the King will pass over may not be under attack, nor
can the square on which the King will land.
I hope this helps!!
Slan...
Imp..