Why two bishops work well together
A single bishop only ever reaches squares of one colour, so the opponent can put pawns and pieces on the other colour and avoid it. Two bishops cover the whole board between them. On open diagonals they attack from long range, protect each other's weak spots and are excellent at stopping passed pawns on both wings.
The advantage is real but modest, commonly reckoned at around half a pawn. It grows as the position opens and as other pieces are exchanged, and it is often clearest in endgames with pawns on both sides of the board.
Playing with the bishop pair
Open the position with pawn breaks, because bishops need open diagonals. Use pawn moves to take squares away from the enemy knights, so they find no outposts. Avoid trading one of the bishops cheaply, since the pair is worth more than the two bishops separately.
Playing against the bishop pair
Keep the position closed and the pawns fixed, so that the bishops have few open diagonals. Look for a secure outpost for a knight. Often the simplest remedy is to exchange one of the bishops, for example by offering a trade of your own bishop of the same colour.
Giving up the bishop pair can be a deliberate choice. In the Exchange Variation of the Ruy Lopez, White gives up a bishop for a knight to double Black's pawns and gain a healthier pawn structure.
Common mistakes
- Keeping the position closed when you have the two bishops, so they have nothing to bite on.
- Trading one of your bishops for a knight without a good reason, which throws the advantage away.
- Assuming the bishop pair always wins. Against a well-placed knight in a blocked position it may be worth very little.
Questions about bishop pair
How much is the bishop pair worth?
It is commonly reckoned at about half a pawn, more in open positions and endgames with pawns on both wings, and less in closed ones.
Is the bishop pair good in closed positions?
Less so. With fixed pawn chains the bishops have few open diagonals, and knights are often at least as useful.