Assuming this is a standard chess game and not a variant, why is this position illegal?
Challenge: Why is this position illegal?
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KieferSmith
Sep 21, 2023
0
#1
Sep 25, 2023
0
#4
theres a thread at fun with chess for this
#5 is the Bb3, cant be original for geometry and white has all 8 pawns so cant be promoted
#7 is the Be5, it has no previous legal move but must have been the previously moved piece
AlekhinesRazor wrote:
I see why: White has 4 pieces (one Q + two Bs on the same color as another B + one N) that could not exist except through pawn promotion, but White is missing only 3 pawns, therefore could not have brought those 4 extra pieces into existence.
That seems quite correct.
illegalthingy wrote:
5 is legal
It's not. There are pawns on e2 and g2, and 8 white pawns on the board, so there's no way the bishop could get to b3.
The thread Ilampozhil25 mentioned, Forums > Fun With Chess > Illegal Position Contest!, is now up to comment #7564. Here's a position that was posted there recently. Someone reading this thread may want to try explaining what makes it illegal.
Sep 26, 2023
0
#9
The bishop cannot get there without somehow have previously checked the king, forcing it off the diagonal, and if the bishop was already on b7, the king could have never got on the diagonal in the first place.
From what I understand, that's an impossible position and impossible positions don't count as illegal.
However, in this case the B could have taken a piece.
Bogo-IndianaJones wrote:
The bishop cannot get there without somehow have previously checked the king, forcing it off the diagonal, and if the bishop was already on b7, the king could have never got on the diagonal in the first place.
That's incorrect. The position of the bishop and white king is not a problem.
Optimissed wrote:
From what I understand, that's an impossible position and impossible positions don't count as illegal.
However, in this case the B could have taken a piece.
A legal position is one that can be reached from the initial array with a series of legal moves. An illegal position is one that's not legal. You'll have to give me the definition of an impossible position, since that's not a concept I'm familiar with.
Yes, come join our "illegal position contest" thread. Much more challenging examples of why positions are illegal, with more subtle reasons like positional timing of pieces and retroactive analysis, contradictory elements of a position..etc.
In the meantime, can anyone here give a valid explanation of why the position at #16 is illegal?
Optimissed wrote:
From what I understand, that's an impossible position and impossible positions don't count as illegal.
However, in this case the B could have taken a piece.
Black could have moved his bishop to a8, then white moves say a knight to b7, and walks his king up to c6. Blacks last move bishop captures knight b7+.
EndgameEnthusiast2357 wrote:
Optimissed wrote:
From what I understand, that's an impossible position and impossible positions don't count as illegal.
However, in this case the B could have taken a piece.
Black could have moved his bishop to a8, then white moves say a knight to b7, and walks his king up to c6. Blacks last move bishop captures knight b7+.
Sounds reasonable. Why is the position illegal?
The black pawns could have only captured on light squares to get where they are.
Wait a second...Promotion...
What if white promoted to a bunch of pieces and placed them to be captured on g6, h5, e6-h3..etc. white could have sacced his queen and still has 5 pawns to promote. The white f pawns could have taken a black piece to get to f5, so that accounts for the 1 piece white needed to have on b7. I'm actually going to say this is legal.
Sep 27, 2023
0
#18
It´s simply not possible for White to promote enough pawns to make pieces for the Black pawns to take. Maybe I´ve overlooked something here?: (note that the LSB must have been taken, since the e and g pawns have not moved)
... and White is still missing one piece to be taken for the check on b7, plus one more to be taken on h3.
Black could sac his rook and queen allowing the a pawn to move around blacks a pawn and promote. Slightly off topic but here's an interesting fact. 6 pawns from each side can pass each other without capturing any other pieces. I know this doesn't apply here but still:
I know in the original position the black pawns have to get there, but just saying.