25 April 2012

Glossary of Tactics: Forks

In chess, a fork is when one piece attacks two targets in different directions. A fork may occur along a rank, file, or diagonal. In such cases, the forking piece will stand between the two targets.*

The knight fork is often the first tactic that beginners use to gain an upper hand on their competition.

Black to move

In the position above, White's knight is attacking Black's queen and Black's rook, a typical knight fork. However, because the knight is unprotected, this fork is not particularly effective. If the knight were secure from capture by the Black king, it would capture one of the two attacked pieces.

The position above comes from the Fried Liver Attack after the moves 1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.exd5 Nxd5 6.Nxf7.

After the usual 6...Kxf7 7.Qf3+, we have a queen fork. The queen attacks both king and the knight on d5. The knight is protected by Black's queen, but is also attacked by White's light-squared bishop. There are two attackers, but only one defender.

Black to move

In order to avoid the loss of material due to the queen fork, Black's king must move towards the center. 7.Ke6. So it is in the Fried Liver Attack. White employs a sequence of forks and other tactics to apply pressure, to provoke and then to exploit a vulnerable king. White sacrifices a knight to initiate these actions.

In most examples of forks in chess books, one piece attacks two pieces. But a fork may include critical targets that are not pieces. For example, in the solution to Problem 44255 on Chess Tempo, a knight forks king, queen, and a critical square.

White to move

White's key move is a queen sacrifice. 1.Qxh6. After 1...Nxh6, the pawn on f6 is undefended. 2.Nxf6 is the winning fork. Although the queen and king are both forked, that is inconsequential. What matters is that the knight controls g8 and h7, forking king and square. After 2...Kh8, White wins with an exchange sacrifice. 3.Rg8+ Nxg8 4.Rxg8#.

Every chess piece is able to fork, even the king. Normally, a bishop and a knight will win against a lone king. But, if the defending king is able to capture either, the position is a draw by insufficient material.

Black to move

Black draws with 1...Kd4. The king attacks both bishop and knight, winning one and leaving White with insufficient material to deliver checkmate.

*Tactics such as pins and skewers attack two targets along a line, a diagonal, file, or rank. Both targets will be in the same direction from the attacking piece.

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