The isolated pawn in chess, or isolani, is a structural element of great importance. Players must learn how to play isolated pawn positions, both as the owner of the isolani and as the side playing against it. Why is it so important to learn these positions? Simply because they occur so often, and because this structural element often comes to dominate the game if all other things between the two sides are roughly equal.
At this point it will be useful to distinguish between the general case of the isolated pawn, and the specific case of an isolated queen's pawn that occurs in many popular openings. This is because in general, an isolated pawn is a significant weakness, but in the particular case of the isolated queen's pawn or IQP, this weakness can become a strength. We will deal with the general case first.
Isolated Pawns - What They Are And Why They're Weak
Simply put, an isolated pawn has no companions on the files on either side of it. Since pawns can only move forwards and can only capture diagonally, this means that the isolated pawn cannot be protected by another pawn, making it a weakness that the other side can focus on. A simple example in a rook and pawn endgame:
+----+----+----+----+----+----+----+----+
| | | | r | | | | |
+----+----+----+----+----+----+----+----+
| | | | | | | | p |
+----+----+----+----+----+----+----+----+
| | | | | | | | |
+----+----+----+----+----+----+----+----+
| | | | | | k | p | |
+----+----+----+----+----+----+----+----+
| p | | | | | | | |
+----+----+----+----+----+----+----+----+
| P | | | P | | | | |
+----+----+----+----+----+----+----+----+
| | | | R | | | K | P |
+----+----+----+----+----+----+----+----+
| | | | | | | | |
+----+----+----+----+----+----+----+----+
Here, although material is equal, Black has the advantage because White's rook is tied down to the passive defence of his isolated pawn, leaving Black free to advance his pawns on the other side of the board, and use his extra space and activity to create other threats to try to win the game. It's not over yet, but Black is the only one who can think about getting a full point — White must sit tight and hope for a mistake. If White's pawn was not isolated and did not need defending, his rook could become active, and the position would be drawn. As a general rule, the weakness of an isolated pawn becomes more apparent as pieces are exchanged off and the endgame approaches. If the rooks come off the board in the example above, it is a clear win for Black.
An isolated pawn can often not be won directly; if material is equal, the side with the isolani can usually defend the pawn sufficiently. The problem with an isolated pawn position is that in chess, being forced into a position of passive defense is very undesirable. In chess, as in military tactics in general, the best defense is a good offense. An isolated pawn can spread paralysis throughout the ranks of its owner, until his entire army is tied down to the defense of the pawn, leaving his opponent more space and freedom to develop attacks in other areas of the board. Another weakness of the isolated pawn lies in the fact that the square directly in front of it can become an unassailable outpost for an enemy piece.
Two isolated pawns on the same file - doubled isolated pawns - are, naturally, even worse. Not only can they not defend each other or be defended by any other pawns, but the pawn in front impedes the movement of the pawn behind. This structure is very weak, and will only be allowed by a player if he gains good compensation from other factors in the position, or if he has no choice. Often, a player will even sacrifice material in order to induce this weakness in the opponent's camp — a good example is in the Dragon Variation of the Sicilian Defense, where in the following position Black sacrifices his rook for White's knight by playing Rxc3, forcing the capture bxc3 which gives Black excellent compensation due to White's ruined pawn structure and the weakness of his King's defenses:
+----+----+----+----+----+----+----+----+
| | | r | q | | r | k | |
+----+----+----+----+----+----+----+----+
| p | p | | b | p | p | | p |
+----+----+----+----+----+----+----+----+
| | | | p | | n | p | Q |
+----+----+----+----+----+----+----+----+
| | | | | | | | P |
+----+----+----+----+----+----+----+----+
| | | | N | | | P | |
+----+----+----+----+----+----+----+----+
| | | N | | | P | | |
+----+----+----+----+----+----+----+----+
| P | P | P | | | | | |
+----+----+----+----+----+----+----+----+
| | | K | R | | | | R |
+----+----+----+----+----+----+----+----+
The Isolated Queen's pawn
This is a structure that arises from a great number of popular opening systems for both sides, including but not limited to the Caro-Kann Defense, the Nimzo-Indian Defense, the Queen's Gambit, the English Opening, the Tarrasch Defense and the Queen's Indian. The reason for the popularity of this structure requires knowledge of a small amount of chess history. When the principles of classical chess were first expounded more than a century ago, the opinion of chess masters regarding the isolated queen's pawn were very much as I've given above with regard to isolated pawns in general — they were regarded as a weakness to be avoided. However, as chess theory and knowledge progressed, it became clear that "static" weaknesses (weaknesses of structure) could be compensated by "dynamic" factors (e.g. freedom of piece movement, control of important files and diagonals). This led to the creation of many new opening systems, or the revival of older, discarded openings whose good points were now better understood. Among these systems were the IQP positions.
The basic IQP position, without pieces on the board, is as follows:
+----+----+----+----+----+----+----+----+
| | | | | | | | |
+----+----+----+----+----+----+----+----+
| p | p | | | | p | p | p |
+----+----+----+----+----+----+----+----+
| | | | | p | | | |
+----+----+----+----+----+----+----+----+
| | | | | | | | |
+----+----+----+----+----+----+----+----+
| | | | P | | | | |
+----+----+----+----+----+----+----+----+
| | | | | | | | |
+----+----+----+----+----+----+----+----+
| P | P | | | | P | P | P |
+----+----+----+----+----+----+----+----+
| | | | | | | | |
+----+----+----+----+----+----+----+----+
- White has more slightly more space, and more central control.
- White's d-pawn (his queen's pawn) is isolated, and can be targeted by Black's pieces.
- White's position is very free - his pieces can develop unhindered.
- Black controls the d5 square in front of White's isolated pawn.
- Black will almost certainly castle on the kingside.
These factors, when taken together with our understanding of isolated pawn positions in the first section, establish the likely character of the game to come. White, with his free development and his extra influence in the centre, will try to activate his pieces to the maximum and create a big attack on Black's king. Black, on the other hand, will try to rely on the solidity of his position, and gradually extinguish the dynamics of the position through exchanging pieces prophylaxis. This tension between opposing strategies and conflicting positional concepts is at the heart of modern chess, and that is why players seek out IQP positions on both sides.
A key strategy for White in IQP positions is one that Black must be vigilant for at all times: he can try to advance his isolated pawn. On d4 it may be a weakness, but if it can advance to d5 it may be exchanged for Black's pawn on e6, eliminating the weakness. It may even be sacrificed on d5 in order to initiate a combinative attack on Black's king, tying up Black's pieces and opening lines in the centre. Because this strategy can be so effective, Black often puts in place a complete blockade of the pawn, in which the square in front of it (d5) is permanently occupied by a black piece that cannot be moved - typically a knight, the ideal blockading piece due to its ability to jump over other pieces. A sample middlegame position of this nature:
+----+----+----+----+----+----+----+----+
| r | | b | q | | r | k | |
+----+----+----+----+----+----+----+----+
| p | p | | | b | p | p | p |
+----+----+----+----+----+----+----+----+
| | | n | | p | | | |
+----+----+----+----+----+----+----+----+
| | | | n | | | | |
+----+----+----+----+----+----+----+----+
| | | | P | | | | |
+----+----+----+----+----+----+----+----+
| | | N | B | | N | | |
+----+----+----+----+----+----+----+----+
| P | P | | | | P | P | P |
+----+----+----+----+----+----+----+----+
| R | | B | Q | R | | K | |
+----+----+----+----+----+----+----+----+
Because there are so many of these kinds of positions, it is often impossible to say which side, if any, has the advantage, or to recommend a sure-fire strategy. The positions are balanced, and the exact moves to be played depend to a great extent on what the opponent does. The general outlines I have given above are a starting point for playing IQP positions, but true expertise only comes with a lot of practice, and studying the games of grandmasters. I will give a game between two ex-world champions below that exemplifies many of the concepts discussed here.
1. c4 c5 2. Nf3 Nf6 3. Nc3 d5 4. cxd5 Nxd5 5. e3 e6 6. d4 cxd4
7. exd4 Be7 8. Bd3 O-O 9. O-O Nc6 10. Re1 Nf6 11. a3 b6
12. Bc2 Bb7 13. Qd3 Rc8 14. Bg5 g6 15. Rad1 Nd5 16. Bh6 Re8
17. Ba4 a6 18. Nxd5 Qxd5 19. Qe3 Bf6 20. Bb3 Qh5 21. d5
This is the thematic advance referred to above, in which White's supposed weakness, his d5-pawn, reveals itself as a powerful weapon once his piece activity has increased enough to generate direct threats on the enemy king.
+----+----+----+----+----+----+----+----+
| | | r | | r | | k | |
+----+----+----+----+----+----+----+----+
| | b | | | | p | | p |
+----+----+----+----+----+----+----+----+
| p | p | n | | p | b | p | B |
+----+----+----+----+----+----+----+----+
| | | | P | | | | q |
+----+----+----+----+----+----+----+----+
| | | | | | | | |
+----+----+----+----+----+----+----+----+
| P | B | | | Q | N | | |
+----+----+----+----+----+----+----+----+
| | P | | | | P | P | P |
+----+----+----+----+----+----+----+----+
| | | | R | R | | K | |
+----+----+----+----+----+----+----+----+
21...Nd8 22. d6 Rc5 23. d7 Re7 24. Qf4 Bg7 25. Qb8 Qxh6 26. Qxd8+ Bf8
27. Re3 Bc6 28. Qxf8+ Qxf8 29. d8=Q and Karpov resigned (1-0)