Pins and Forks
Pins
A pin is the position that occurs when there is an attacking piece in sight of a defending piece that can not move without exposing a more valuable defending piece. "To pin" is the action of moving the attacking piece into position.
Unlike the fork, there are only three pieces than can perform a pin. The bishop, queen, and rook. This is because these pieces move in long straight or diagonal lines. Knights and pawns can not pin, although they can still initiate a pin by moving out of the way of a well-positioned bishop, queen, or rook.
Any piece can become pinned, but typically the more valuable piece on the other side of the pin is either the queen or the king. A pinned queen will also mean that the pinned piece is at least somewhat defended. It is much better to keep a pin than to take an even trade in pieces.
An absolute pin is a pin in which the more valuable piece behind the pinned piece is none other than the king. It is actually against the rules of the game to move a piece that is pinned in front of the king, as this would put the king in check and on the next move would theoretically be taken.
Any time you can successfully perform a pin it is almost certainly the best choice to do so. A pin does substantial damage to the mobility of a players pieces, even if does not actually remove them from the game.
Forks
Creating a successful fork will effectively end most chess games.
A fork is the maneuver by which one piece makes two or more attacks simultaneously. Most of the time, this forces the defending player to sacrifice at least one of the forked pieces. Forks are most powerful when one of the pieces under attack is the king. The defending player will have to move the king out of check, guaranteeing the potential to take the other forked piece.
If the king is not one of the units under attack in the fork, it is possible to escape. If one of the pieces caught in the fork can escape, and in the same move put the enemy king in check, this will give the defender time to move away the second forked piece on the next move.
The fork is preformed most often with the knight. The knight can attack up to six squares at a time, not as many as the bishop or rook, but the squares the knight can attack are located around it in a circle. This radius attack allows forking the king and another opponent piece even though they are separated or defended by other pieces.
