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Isolated pawn

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White's pawn on the e-file and Black's pawn on the a-file are isolated.

In chess, an isolated pawn is a pawn which has no friendly pawn on an adjacent file. An isolated queen's pawn is often called an isolani. Isolated pawns are usually a weakness because they cannot be protected by other pawns. However, there can be compensation, such as improved development and associated opportunities for counterplay, that offset or even outweigh the weaknesses associated with the pawn's isolation.

Many "textbook" openings lead to isolated pawns, such as the French Defence, Nimzo-Indian Defence, Caro-Kann and Queens Gambit.

Weakness

In the endgame, isolated pawns are a weakness in pawn structure because they cannot be defended by other pawns as with connected pawns. In this diagram, the white pawn on the e4 square and the black pawn on a7 are isolated.

Isolated pawns are weak for two reasons. First, the pieces attacking them usually have more flexibility than those defending them. In other words, the attacking pieces enjoy greater freedom to make other threats (win pieces, checkmate, etc.), while the defending pieces are restricted to the defense of the pawn. This is because a piece that is attacking a pawn can give up the attack to do something else, whereas the defending piece must stay rooted to the spot until the attacking piece has moved. The defending piece is thus said to be "tied down" to the pawn.

The second reason is that the square immediately in front of the isolated pawn is weak, since it is immune to attack by a pawn (often providing an excellent outpost for a knight). Thus an isolated pawn provides a typical example of what Wilhelm Steinitz called weak squares.

Isolated queen pawn

An isolated queen pawn (IQP), called an isolani, is often a special case. An isolated queen pawn is one in the queen's file (d-file). The weakness of such a pawn's isolation arises from two factors associated with the absence of both neighboring pawns:

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White has an isolated queen pawn, but better piece development (Kramnik-Kasparov, 2000)

  1. Because the pawn is on one of the board's two central files (i.e., the d- or queen file), it blocks the opponent's control of that file and attacks or defends the other central file (i.e., the e- or king file). Given the strategic and (usually) tactical importance of control of the center, the pawn is important enough that the player must consistently defend it, but with no pawns available for its defense, the player must "tie down" a minor or major piece (in the opening, usually the king's knight or the queen) with that task.
  2. Similarly, when the isolani is on the third or fourth rank, such that the square ahead of it is on the fourth or fifth rank (i.e., d4 or d5 respectively for White and the reverse for Black), the absence of adjoining pawns prevents the player from attacking or defending that square with pawns. Because each square is one of the board's four central and most important squares, the player will frequently be required to keep one or more pieces committed to the square's attack or defense.

However, the presence of open files in the important king and queen's-bishop (e and c) files as well as the outposts at e5 and c5 enable the player with the IQP very favourable attacking chances in the middlegame. Once the game reaches the endgame the isolated nature of the pawn becomes a greater weakness than these strengths. Therefore, the player with the IQP must take advantage of the temporary strength before an endgame is reached. With four minor pieces each, an IQP is an advantage; with three minor pieces each, it is about even; and with two or fewer minor pieces each, it is a disadvantage (Gallagher 2002:140). Sacrifice of the pawn by White and blockade of the pawn by Black are common themes.

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