Retrograde analysis is a problem-solving technique that involves working backwards from a given position to determine the sequence of moves that led to it. By using logical deduction and creative thinking, players can reconstruct the history of a game and gain a deeper understanding of the strategic and tactical nuances of chess. Retrograde analysis is an important tool for chess players of all levels, as it helps them develop their analytical skills and improve their overall game.
We devoted a couple of short sessions exploring the amazing world of retrograde analysis. Below are a few retrograde analysis puzzles we tried to solve. There are also some great books on the subject.
1. Prove that a white pawn reached the 8th rank.
Hint
How did the white bishop get to g3?
Solution
When the game started a white bishop was located on c1. But since the b2 and d2 pawns never moved there is no way for that bishop to get to g3. Therefore the bishop on g3 is a promoted piece. Therefore at some point during the game some pawn promoted to a bishop that found its way to g3.
2. White to move and checkmate in one move. Where is the white queen located?
Hint
There is no way the queen made it past the pawns. Therefore it must still be in the first rank.
Solution
Since none of the pawns have moved the queen must be in the first rank. And since the king and queen couldn't have swapped spaces the queen must be on either a1, b1, c1 or d1. The only space where there is a checkmate in one is when the queen is located at a1. And the checkmating move is pawn to b2.
3. What was black’s last move?
Hint
If the king arrived from a7 what was white's last move? Remember, in retrograde chess pieces can suddenly appear on the board as a result of a capture.
Solution
The black king must have come from a7 in the last move. But then what was white's last move? Well it couldn't have been a bishop move because the black king would have been in check. Nor could it be a King move because again the black king would have been in check. And the pawn hasn't moved. It must be that there was another white piece on a8 that the black king captured. The only piece that could have been moved to a8 would have been a knight from b6. So there was a knight on b6 that moved to a8 resulting in check. And the black king moved to a8 to capture it.
4. Both sides have made exactly 4 moves. What moves were they?
Hint
The current knight on b8 traveled all the way from g8!
Solution
This was the game: 1. Nf3 Nf6 2. Nd4 d5 3. Nc6 Nd7 4. Nxb8 Nxb8
