The pawn structures often define the ways in which the middlegame battle will be carried out. In many openings, the pawns form chains of pawns. In order to understand the nature of the pawn chain, we use the somewhat violent analogy to shooting birds. When three birds fly overhead in formation, the best strategy for a large holiday meal is to shoot at the bird in the rear. The other birds may hear the shot, but they won't actually see that the bird in the rear was shot.
In chess, the pawn in the rear of the chain is the weakest of the pawns precisely because the other pawns can no longer protect it. The best strategy, therefore, is often to aim your attack at the rear of your opponent's pawn chain. In the following diagram, black has prepared and will now play the move ...c5. If white should capture this c-pawn, both of white's pawns will be weak and subject to capture.
Here is a more practical example. White, on the attack, moves the pawn to e6 where it attacks the base of the black pawn chain. If black captures the pawn, white will be able to respond with Qxg6 check!
