In particular, we’re going to discuss the same-color bishop endgame. The attacking side has one pawn, and the defender has none.
If the defender can sacrifice their bishop for the last pawn the game is drawn, so the attacker must proceed carefully.
What the Defender Wants in this Ending
The position is completely drawn if the defending king can reach a square in front of the pawn opposite the color of the bishops. The king stays put and the defender moves their bishop around forever … or until they can call over the Arbiter or TD and claim a draw. Here’s an example:
Things get much more complicated if the defending king is behind the advancing pawn. In that case, the bishop desperately tries to control a square the pawn needs to cross in order to prevent it from queening. The attacking king and bishop look to attack the defending bishop, forcing it to move and give up control of the pawn’s path.
This is why you nearly always want your king to blockade passed pawns in the endgame: he can control all of the squares around him, and it’s harder to push him away than a rook, bishop, or knight!
A Worst Case Scenario
Anyway, a plausible scenario is the following:
This is a famous endgame study by Genovese composer Luigi Centurini (1820-1900) published in 1856. You’ll find it in every endgame encyclopedia, for example Basic Chess Endings, Dvoretsky’s Endgame Manual, and Magnus Carlsen’s favorite Fundamental Chess Endings … but for years I didn’t quite understand it.
The Black bishop can stop the pawn on either the long b8-h2 or mini a7-b8 diagonal. If White can gain control of both diagonals, the Black cleric will be unable to stop the pawn.
Chase the Bishop!
More Room to Operate
Notice that Black lost because of the short a7-b8 diagonal. To draw, Centurini taught us that the defender usually needs both diagonals to be at least four squares in length. Then, there will always be at least one square on one of the diagonals that the attacker cannot control.
Here’s a famous example of successful defense:
Hopefully you now understand this classic bishop endgame if you previously struggled with it!