isolated pawn. 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 on the queen's (d-file). Its weakness arises from two factors: Given the strategic and (usually) tactical importance of control of the centre, 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 or (in the opening, usually the king's knight or the queen) with that task. Similarly, when the isolani is on the third or fourth rank, the absence of adjoining pawns prevents the player from attacking or defending the square ahead of it (e.g. for White, squares d4 or d5, respectively). Because these squares are important squares, the player will frequently be required to keep one or more pieces committed to the square's attack or defense. The presence of open or half-open king (e-) and queen's bishop (c-) files, however, as well as the outposts (for White) at e5 and c5, enable the player with the IQP favourable attacking chances in the middlegame. Once the game reaches the endgame, the pawn's isolation becomes more of a weakness than a strength. Therefore, the player with the IQP must take advantage of its strength before an endgame is reached. proposed that with four 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. Sacrifice of the pawn by White and of the pawn by Black are common themes. Strategy The diagram shows some of the optimum piece placements for both sides in an IQP position. White has rooks placed on the open c-file and semi-open e-file. has a knight ready to jump into the e5-square which the IQP supports. This can be a jumping-off point for an attack. has two pieces controlling the weak d5-square in front of the IQP (queen's knight and light-squared bishop). has three pieces preparing the thematic d4–d5 advance (queen's knight, light-squared bishop, and queen). has pinned the f6-knight against the black queen with the dark-squared bishop on g5 reducing Black's control of the crucial d5-square. Making use of this arrangement of pieces White may plan to either advance thematically with d4–d5 opening the position