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In this video, the goal is to prove that black CANNOT castle. To do this, one must show that the King or the Rook must have already moved. If you want to see more retrograde puzzles, let me know! Be sure to subscribe for more chess content!
Thank you!
Here is the PGN to reach the position in a game:
1. Nc3 Nc6 2. Na4 Ne5 3. Nb6 Nf3+ 4. gxf3 g5 5. Nxc8 g4 6. Nb6 g3 7. Bh3 Bg7 8.
Nc4 Nf6 9. Bf5 Nd5 10. Bd3 Nf6 11. Nh3 g2 12. Rf1 g1=R 13. a4 Rg3 14. hxg3 Bh6
15. b4 Be3 16. fxe3 Rg8 17. a5 Rg5 18. b5 h5 19. c3 h4 20. g4 Rh5 21. g5 Rh6 22.
g6 Rh5 23. g7 Nh7 24. g8=R+ Nf8 25. Rg2 Rh6 26. Bc2 Rh7 27. d3 Rh8
28. Ra4 Rh7 29. Ba3 Rg7 30. Bb4 Rg6 31. Bb3 Rg8 32. a6 Rg7 33. b6 Rg8 34. Na3
Rg7 35. c4 Rg8 36. c5 Rg7 37. c6 Rg8 38. Ra5 Rg7 39. Bc4 Rg8 40. Bb5 Rg7 41. Rg4
Rg8 42. Bc5 Rg7 43. Rga4 Rg8 44. Bb4 Rg7 45. Qb3 Rg8 46. Kd2 Rg7 47. Ra1 Rg8 48.
Ra2 Rg7 49. Kc2 Rg8 50. Kb2 Rg7 51. Ka1 Rg8 52. Nf4 h3 53. Nd5 h2 54. e4 h1=N
55. Ne3 Ng3 56. d4 Rg6 57. Nec2 Rg5 58. Ne3 Rc5 59. dxc5 Nf5 60. Nec4
Ne3 61. Nd2 Nd5 62. exd5 Ng6 63. d6 Nf4 64. e4 Nd5 65. exd5 Kf8 66. Ndc4 Kg7 67.
Kb2 Qh8 68. Kc2 Kf8 69. Kb1 Ke8 70. Kc2 Qe5 71. f4 Kf8 72. fxe5 Ke8 73. Kb1 Kf8
74. e6 Ke8 75. Ka1
Chess Logic Puzzle ♚ Is Castling Legal? ♚ Retrograde Puzzles
I would argue that there are no positions where it is possible to prove that castling is legal. In any position where the king and at least one rook stand on their original squares, you can never be sure the pieces didn't move and return to their original squares. So for a retrograde puzzle asking if castling is possible, the only way it could be solvable is if castling is impossible. For this puzzle, "no solution" isn't given as one of the choices, so I guess castling must be impossible.
but at 4:54 the h pawn might have promoted and then moved wth
Fun fact, if it's whites move its M6: QH3, EXD6; QH8, KE7; CXD6+, CXD6; BXD6#
I think my stockfish is tweaking out of it's blacks move because it says 51.3, but then M3 after black moves the king to F8 (which is it's top choice)
What if black went with those h and g pawns out further then white, then brought their rook to let white pawns slide to the side? Could it work like that, since black pawns could go then?
Actually, the h-pawn can be taken, but only by virtue of promotion. (Same for the g-pawn). However, in order for both h-pawns to promote, the white h-pawn must either take the g-pawn, or take after the g-pawn has passed. Therefore, there are six capturable pieces if the king hasn’t moved, but seven required pawn captures to reach this position. Therefore, the king must have moved out in order to let the queen be the seventh pawn capture.
The rook is promoted, it'd be checkmate if the king is in this position, so in conclusion the king wasn't there when the pawn promoted
The initial position could have been black playing at a disadvantage, with a king, rook, and 6 knights. This eliminates your logic…
It is still possible to think about how white got its third rook, without getting a backrank mate, but we can assume that it blocked its own rook with something like a bishop or a knight so that it could not attack.
Well because theres a 3rd rook, the black king would have moved otherwise it would be checkmate
But we already know it has moved because how the Frick would the queen and bishop get out if it hasnt
what pawn could capture the black g pawn to the left?
I simply went “but black’s white square bishop couldn’t have ever left unless if the king moved right?”
How is the black h pawn promoting ruled out?
Of course why will castle not be legal in that position
H7 pawn can be premoted and can sacrifise
The black pawns could promote and then they are free to get captured I think
You should have explained first why the simple logic "Queen and bishop must have exited without any of the pawns moving, therefore the king must have moved to make space" is wrong.
If black's g and h pawns promote then they can be captured by white's pawns
I love retrospective chess
The pawns can promote right? Like it seems completely possible without the king moving if the pawns promote
ok easier way is
you cant get the damn bishop out in the first place, how do you get to this position
Couldn't the black H and G pawns have been promoted, then captured?
Can’t black’s h pawn promote to a different piece and then get captured?
Thanks for doing that! There is very little retrograde chess content on YouTube and I really enjoy these puzzles.
Couldn't both black's g and h pawns promote? That would make 6 captures. The black knights can help move the pawns out of the way beforehand.
Edit: Nevermind, this isn't possible because white's h pawn is in the way, and you'd need to make one side capture an extra piece to make sure they pass each other.
As others have mentioned, the way you have presented it doesn't consider promotion. I think the simplest logic is to realise that 6 leftward pawn captures are required. For the black h pawn to be left captured, it must promote which means the white h pawn must left capture to open the file. This uses up one of the six required captures, meaning the problem is impossible unless the h pawn can then be in the final pawn structure, and it is impossible to include the h pawn in the final pawn structure without 7 total captures.
It can't castle because the black bishop would be trapped, so the king needs to move so another piece can capture the black bishop
I’m sorry, but how do you even have 3 rooks and all pawns? Isn’t it necessary to promote a pawn to have an extra piece?
Wait, couldnt just the h and g pawns have promoted and then gotten captured?
This board position is perfectly describable as "what the hell happened here"
Blacks queen could have been captured by a knight so black king didnt need to move
black h pawn might have been promoted and resultant figure sacrificed at a later stage, at the right moment. So the conclusion may not be correct.
I didn’t watch the whole video sorry, hoe did black’s bishop get out?
I tried to recreate the position but couldn't find a way to get the light squared bishop out for the 6th recapture.
1. a4 Nf6 2. a5 Nc6 3. b4 Nb8 4. b5 Nc6 5. a6 Nd4 6. b6 Ne6 7. c4 h5 8. c5 Ng4 9. c6 Nf6 10. d4 Nf4 11. d5 Ne6 12. d6 Nf4 13. e4 Ng6 14. e5 Nf4 15. e6 Ng6 16. Ra5 Nf4 17. Na3 g5 18. Bb5 N6d5 19. Bd2 Ne3 20. fxe3 Bg7 21. Bb4 Bd4 22. exd4 Rh6 23. Qb3 Ne2 24. Nf3 Nc3 25. Nd2 Ne4 26. Ndc4 Nc5 27. dxc5 Rf6 28. Rf1 Rf3 29. gxf3 Kf8 30. Rg1 Kg7 31. Rf1 Qh8 32. Rh1 Kf8 33. Rg1 Ke8 34. Rxg5 Kf8 35. Kd1 Ke8 36. Kc1 Kf8 37. Kb1 Ke8 38. h4 Qh7+ 39. Ka1 Kf8 40. Rxh5 Qe4 41. fxe4 Kg7 42. Rf5 Kg8 43. Rf2 Kg7 44. Nb1 Kg8 45. Rfa2 Kg7 46. R2a4 Kg6 47. Nba3 Kg7 48. h5 Kh7 49. h6 Kg6 50. h7 Kg7 51. h8=R Kg6 52. Rh2 Kg7 53. Ra2 Kf8 54. Kb2 Ke8 55. Ka1
Isn't it enough to say that the only way the bishop and queen can get out is by the king moving? Since the black a-f pawns clearly haven't moved?
Why are we assuming that those two pawns are the f and g pawns? It's perfectly possible that they were the c and d pawns, and the pawns in the sixth rank are a, b, e, f, g. This would require the e, f, and g pawns to only capture one piece/pawn each, for three captures total.
It is possible for black to castle, here’s the PNG to prove it. It isn’t quite efficient, I made a lot of stalling moves with black to allow white to do what it needed to, but it worked out in the end.
1.Nc3 Nh6 2.Nb5 Ng8 3.Nd4 Nh6 4.Nc6 Ng8 5.Nxd8 Nh6 6.Ne6 Ng8 7.Nd4 Nh6 8.Nb5 Ng8 9.Na3 Nh6 10.Nc4 Ng8 11.Nb6 Nh6 12.Nxc8 Ng8 13.Nb6 Nh6 14.a4 Nc6 15.a5 Ne5 16.a6 Nc6 17.b4 Ne5 18.b5 Nc6 19.c4 Ne5 20.Na4 Ng6 21.b6 Ne5 22.c5 Ng6 23.c6 Ne5 24.d4 Ng6 25.d5 Ne5 26.d6 Ng6 27.e4 Ne5 28.Nc3 Ng6 29.e5 Nf4 30.e6 Ng6 31.Ra5 Nh4 32.Bb5 Ng6 33.Bd2 Nh4 34.Nd5 Ng6 35.Bb4 Nh4 36.Nf3 Ng6 37.Ke2 Nh4 38.Qb3 Ng6 39.Rha1 Nh4 40.R1a4 Ng6 41.Ne3 Nh4 42.Nc4 Ng6 43.Na3 Nh4 44.Kd1 Ng6 45.Kc1 Nh4 46.Kb1 Ng6 47.Ka1 Nh4 48.Nd4 Ng6 49.Nf3 Nh4 50.Nd2 Ng6 51.Ndc4 Ne5 52.Nd2 Nf3 53.gxf3 g5 54.Ndc4 g4 55.Nd2 g3 56.Ndc4 g2 57.Ka2 g1=Q 58.Kb2 Qg4 59.Ka1 Qe4 60.fxe4 Ng4 61.Nd2 Ne5 62.Ndc4 Nf3 63.Nd2 Ne5 64.Ndb1 Nc4 65.Nd2 Ne3 66.fxe3 f5 67.Ndc4 f4 68.Nd2 f3 69.Ndc4 f2 70.Nd2 f1=Q+ 71.Kb2 Qg2 72.h4 Qg5 73.hxg5 h6 74.g6 h5 75.g7 h4 76.g8=R h3 77.Rg2 h2 78.Rf2 h1=Q 79.Re2 Qf3 80.Ka1 Qf4 81.Nf1 Bh6 82.Ng3 Bg5 83.Nf1 Bh4 84.Nh2 Be1 85.Nf3 Bc3+ 86.Ka2 Bd4 87.Ng1 Bc5 88.Nf3 Qe5 89.Ng1 Qd4 90.exd4 Rh7 91.dxc5 Rh6 92.Ka1 Rh5 93.Ra2 Rg5 94.Ne2 Rh5 95.Ng3 Rg5 96.Nf1 Rh5 97.Ne3 Rg5 98.Nec4 Rd5 99.exd5 O-O-O
(Black to play, by the way.)
Three rooks -> white has already promoted
wait but the h pawn could have promoted allowing it to be captured, (I see why but that wasn't explained or brought up)
Wait, couldn’t the two missing black pawns have promoted and then gotten captured? That’d still allow 6 captures, right?
Wait.If the kings and the room havent moved,how would the queen come it?
I think it is possible that the h pawn can promote. So black can stil castle!
But if a g7 soldier also beat him, and black did not hit any white tool, then how is he one of the tools beaten by white if he can not get to be one of them?
Great puzzle, but the video's explanation is incomplete. To prove Black can't castle, we can show that the opposite assumption leads to an impossibility (i.e. proof by contradiction).
Each statement follows logically from the rules of chess and the statements above it:
– Black can castle (assumption).
– Black's King and QS Rook have not moved.
– None of the Black a-f pawns have moved.
– Black's Queen and LS Bishop were stuck behind the pawns and King, so they had to have been captured by a White knight.
– In order to reach the final position, the White d-g pawns have collectively made 6 leftward captures. Other options require more captures.
– Black only has 6 pieces for these captures (2 knights, Bishop, Rook, 2 pawns) so they must be used for this purpose.
– The Black g/h pawns have to promote in order to be captured leftward by those pawns.
– The White h pawn has to promote to a Rook and can't capture anything.
– No White pieces can be captured.
– Both h pawns must promote, but neither can (capture to) move out of the way.
The last statement is impossible, so the starting assumption must be false. The final position is unreachable unless Black loses castling rights to let out the Queen or Bishop.
What happens if white's h-pawn takes black's g-pawn (perhaps en passant) and then black's h-pawn? Do you still have black's king required to move?
Is there any way to prove that either of the missing black pawns had run down the board and gotten promoted such that they could move to a place where white’s pawns could capture, or is that not possible either?
Black Bishop and Queen died by enemy capture (Bishop at the birth place). This could only happen only when King moved and made way for the enemy to capture Queen or allow the Queen to die somewhere else after coming out. Castling is not allowed once either King or Rook moves though they return to the original squares. Simple.
How is it possible that the bishop on c7 can leave its start Position?
Very interesting, but how can Black keep this position while white Ccmes in this Position. It needs a coupe of moves to get white in this position.
I didn't read all the comments, but some reading have just made me disagree more.
My point is, isn't it possible that the white h pawn captured a piece, emptied the file and let the black h pawn promote without capturing anything.
Then the promoted piece that used to be the black h pawn, helped any of the white pawns to go "left".
That's why for me, the h pawn, and the g pawn shouldn't be cancelled from the 6 captures count.
It's the point discussed at 04:30