Chess tactics

In chess, tactics in general concentrate on short-term actions or plans. Tactics are so short-term that they can be determined in advance by a human player or by a computer as a specific sequence of moves and all their contingency or alternative moves, starting from a specific position in a game and the fact on who moves next, to achieve a certain goal or advantage for a player in a game. The possible depth of calculation depends on the player's ability or speed of the processor. In quiet positions with many possibilities on both sides, a deep calculation is not possible, while in "tactical" positions with a limited number of forced variants, it is possible to calculate very long sequences of moves.

Simple one-move or two-move tactical actions — threats, exchanges of material, double attacks etc. — can be combined into more complicated variants, tactical maneuvers, often forced from one side or from both. Theoreticians described many elementary tactical methods and typical maneuvers, for example pins, forks, skewers, discovered attacks (especially discovered checks), zwischenzugs, deflections, decoys, sacrifices, underminings, overloadings and interferences.

A forced variant which is connected with a sacrifice and usually results in a tangible gain is named a combination. Brilliant combinations — such as those in the Immortal game — are described as beautiful and are admired by chess lovers. Finding a combination is also a common type of chess puzzle aimed at development of players' skills.

Types of tactics

Tactics are maneuvers in chess that are usually used to gain material, avoid loss of material, checkmate the opponent, or avoid checkmate or loss of a game. Some examples include

• Fork: A move where one piece is moved to attack two or more opposing pieces simultaneously, in the hope that the opponent will only be able to move one of his/her pieces from the attack and leave the other piece(s) available for capture. Any type of piece can fork an opponent's pieces. A fork may or may not involve a check of the opponent's king as one of the pieces being attacked. The general type of fork is named after the type of piece moving to simultaneously attack. For example, in a knight fork, a knight is moved to simultaneously attack two or more opponent's pieces.

• Pin: A piece is considered "pinned" when it cannot move, because, by moving, it would expose a valuable piece to capture. The opponent's attacking piece is the one that pins. There are a couple of ways of classifying pins. A pin can be a partial pin or complete pin; alternatively, a pin can be an absolute pin or relative pin. In a partial pin, the pinned piece can still move along the line of attack, but not off the line of attack without exposing the piece behind it. In a complete pin, the pinned piece cannot move at all without exposing the piece behind it to possible capture. An absolute or "hard" pin is when a piece is pinned to the king, and thus cannot legally move; whereas a relative or "soft" pin occurs when the piece is pinned to a valuable piece, such as the queen.
  
  Additional attacks on the pinned piece by the opponent may be called working the pin. Only pieces that move an indefinite number of squares in a line can pin an opponent's piece; therefore, only a queen, bishop, or rook can pin. Any type of piece except a king can be pinned. It is also possible to pin an opponent's piece in more than one direction, with possibly one of the directions involving an absolute pin. It is also possible for two opposing pieces to partially pin each other along the same line of attack.
  
  Unpinning or breaking a pin on a pinned piece may possibly be done by capturing the opponent's pinning piece or moving the piece behind the pinned piece out of the line of attack or move another blocking piece into the line of attack.

• Skewer: A skewer occurs when a piece attacks an opponent's valuable piece in order to force it to move, and thus capture an opponent's piece located behind. Only pieces that move an indefinite number of squares in a line can skewer an opponent's pieces; therefore, only a queen, bishop, or rook can skewer. Placing the king in check with a rook or queen, and forcing it to move, in order to take a rook that is located behind the king, is an example of a skewer.

• Discovered attack: A discovered attack occurs when a player's piece moves out of the way of (unblocks) a linear attack by one of his/her pieces on an opposing piece. If the unblocked attack is on the opponent's king, this move is called a discovered check. The piece moving out of the way may also cause an attack of its own, resulting in an overall double attack by that player. It is also possible to have a discovered attack with check in which a player moves a piece to check the opposing king but simultaneously unblocks a linear attack on an opposing piece with another of the player's pieces. A variation is a double check, where both the unblocking piece and discovering attack piece check the opposing king simultaneously on the same move.

• Exchange: An exchange [of pieces] occurs when each player captures an opponent's piece in a sequence of closely related moves. Exchanges may be used in combination with other tactics to gain an advantage or avoid incurring a disadvantage.

• Counterattack: A counterattack is a response to an attack with an opposing attack, often just as serious or more serious, perhaps a check. It may sometimes work as a defensive maneuver to avoid net loss of material from another tactic.

• Sacrifice: A deliberate giving up of a piece by its player, allowing or forcing the opponent to capture it, possibly in exchange for a less valuable opposing piece. Any kind of piece except a king can be sacrificed.

• Combination: A series of sequential moves which may involve any combination of tactics leading to checkmate, some other gain, or avoidance of loss.

• Forced three-fold repetition or forced stalemate for a draw to avoid loss of a game. Forced three-fold repetition is sometimes done by repetitive or prepetual check.