Two pawns on one file

White wins White to move · Endgame principles · Difficulty about Elo 1300

The plan

White has two pawns against one and wins — but only because the two stand SIDE BY SIDE. The same position with both pawns on the b-file is, measured, a draw, and no move in the world changes that. The reason is concrete: side by side, two pawns defend each other and eventually create a passed pawn; one behind the other, the rear one can never defend the front one and never overtake it, and the enemy king only has to guard a single file. Measured over sixty thousand random positions of this kind: with doubled pawns the stronger side wins in sixty-eight percent, without them in seventy-seven — the draw rate simply doubles. The first move here is the only winning move out of eight and lines the pawns up side by side. After that comes the second thing you need to know: the pawns wait until the king has arrived. Whoever pushes them on at once gives the win back.

Rule of thumb: two pawns side by side are worth more than two one behind the other — and if you have the choice of how to recapture, recapture so that no doubled pawns arise. Compare 'The doubled pawn as a tempo reserve' — there it is, exceptionally, useful.

Why this level: Two pawns on one file are not two pawns

The solution, move by move

1. 1. a4 The ONLY winning move out of eight. The rear pawn goes to the neighbouring file and thereby stands beside its comrade instead of behind it. All seven other moves are only a draw — including advancing the b-pawn (sidelines).
   Sideline 1. b5 The impatient move: the front pawn runs off. This finally puts the two one behind the other, because the a-pawn can never get past it again. 1… Kc5 The black king places itself in front of it. A pawn that cannot be defended is simply blockaded. 2. Kg2 Kb4 The king grabs the pawn while the other stands too far back. A draw.
   Sideline 1. Kf2 The king marches off without arranging the pawns — the right idea, the wrong order. 1… Kb5 The black king attacks the undefended b-pawn, and the a-pawn on a2 cannot defend it. 2. Ke3 Kxb4 Pawn gone, a draw. That is exactly what the first move was for: the rear pawn has to go to the neighbouring file WHILE there is still time for it.
2. 1… Kc6 The black king rushes up. It now has to guard two files instead of one, and it cannot.
3. 2. Kf2 Now do NOT push the pawns on, but bring up the king. Only two moves hold the win, and the pawn advance is not one of them (sideline) — a pawn move is final, a king move is not.
   Sideline 2. a5 The second pawn runs along instead of waiting for the king. Of seven moves here, only two hold the win — and both are king moves. 2… Kb5 The ONLY move that holds for Black: the king places itself between the two pawns and attacks both. 3. Kf2 c5 And now, instead of capturing, run on itself — only the two pawn moves hold. White has two pawns that can no longer help each other, Black has one that runs: a draw. Pawns cannot go back — every pawn move is a decision forever.
4. 2… Kb6
5. 3. Ke3
6. 3… Kc6
7. 4. Kd4 The king comes closer and closer. The pawns meanwhile stand safe: one defends the other as soon as it becomes necessary.
8. 4… Kb6
9. 5. Kd5 The king goes around the black one and takes its squares away. That is the real work — the pawns have not taken a single step yet.
10. 5… Kb7
11. 6. Kc5 Now the white king stands in front of its pawns and the black one has been pushed away.
12. 6… Kc8
13. 7. b5 Only now may the pawn run, defended by its neighbour and escorted by the king.
14. 7… Kb7
15. 8. a5 The ONLY winning move: the second pawn comes up, the two defend each other, and one of them becomes a queen. With two pawns on the b-file there would have been nothing to get here.

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