Is There a Logical Fallacy In Chess?

[Pargat Perrer]

In the course of testing a chess variant engine, the following position came up which I will reduce down to the key pieces:

White has Rook on d2, Rook on f1, King on h1.
Black has King on d8, Queen on d5.
It is White's move.

If the last move played was ...Qd5 (from what square it doesn't matter), the move is actually ...Qd5+.

How would you explain to a beginning chess player if he or she tried playing Rff2 instead of Rxd5+? How to explain that Rff2 is illegal?

Is this a logical fallacy in chess?

If it were a White Knight on h1 instead of the King, White could play Rff2 and not worry about the h1 Knight because the Black Queen is pinned.
Yet the White King on h1 is considered to be in check!
This is the logical fallacy.
White's King can be captured.... by an ILLEGAL MOVE.
My engine doesn't think it is check because the Black Queen is pinned. And I tend to agree!

Is there a specific clause in the official rules of chess that covers this? A rule that says something like "the first player to have his or her King captured loses the game"?

There must be, because every chess engine and every chess player will consider the White King to be in check in the given position.

I wonder how drastically things would be changed, maybe even some openings, if White were NOT considered to be in check in positions like this?

[Peter McKillop]

.....

How would you explain to a beginning chess player if he or she tried playing Rf2 instead of Rxd5+? How to explain that Rf2 is illegal?
.....

The rule is that the check takes precedence and must be dealt with before anything else can happen. If the check can't be dealt with then the game is over due to checkmate. The fact that White, in your example, is pinning the Black queen does not alter this. Nothing illogical about this.

[Fred Harvey]

Perhaps I'm missing something here, but the aim of chess is to capture the opponents king, whereupon the game is over. The pin is completely irrelevant.

[Peter McKillop]

Perhaps I'm missing something here, but the aim of chess is to capture the opponents king, whereupon the game is over. The pin is completely irrelevant.

The aim of the game is to **checkmate** your opponent's king, whereupon the game is over. Right? You check your opponent's king and if the opponent has no legal move to stop the check, then the game is decided in your favour by way of checkmate. You don't physically capture your opponent's king because that would entail your opponent having to make an intervening, illegal move.

[Pargat Perrer]

The rule is that the check takes precedence and must be dealt with before anything else can happen. If the check can't be dealt with then the game is over due to checkmate. The fact that White, in your example, is pinning the Black queen does not alter this. Nothing illogical about this.

But Peter, look at it from the point of view of someone programming an engine and implementing the rules.

The rules say a piece pinned against the King cannot move while the pin is in place. So I brought up the example of the White King on h1 being a Knight instead of a King, and the engine would realize that the Knight cannot be taken. So White can leave it there and can safely not even bother to defend it. It cannot be captured!

But suddenly the Knight becomes a King and voila, it can be captured! Please explain how you don't see a logical fallacy there?

The point is, from the point of view of the programmer implementing the rules THERE IS NO CHECK OF THE KING. An illegal move cannot constitute a check.

But there must be a specific rule in the Officlal Rules of Chess that addresses this, because everyone in chess agrees that there IS a check. I'd like to see that specific rule so I can know how to implement it.

But I don't think I will implement it, because it is a fallacy. Since the Queen cannot move off the d-file, there cannot be a check of the King.

[Pargat Perrer]

The aim of the game is to **checkmate** your opponent's king, whereupon the game is over. Right? You check your opponent's king and if the opponent has no legal move to stop the check, then the game is decided in your favour by way of checkmate. You don't physically capture your opponent's king because that would entail your opponent having to make an intervening, illegal move.

If it is an illegal move to move your King into check, then it must be an illegal move to move another piece when that move exposes your King to check.

Otherwise there is a logical fallacy.

Somewhere in the Rules of Chess it must say in effect: "It is not an illegal move to expose your King to check if that move is itself capturing the opposing King." In that case, Peter, the CAPTURE of the King, not any check of the King that may or may not be checkmate, reigns supreme.

If there is no such rule written in the Official Rules of Chess, then I suggest we have had things wrong this whole time. By "we" I mean everyone who plays chess or organizes chess and agrees that in the position I have given in this thread, White's King is in check and must move or have the check blocked.

[Pargat Perrer]

Perhaps I'm missing something here, but the aim of chess is to capture the opponents king, whereupon the game is over. The pin is completely irrelevant.

Yes, Harvey, that is how everyone in chess agrees to interpret things.

What I want to see is the exact rule in the official rules that makes this clear. I'd really like to see how this is worded in the official rules.

[Pargat Perrer]

Yes, Harvey, that is how everyone in chess agrees to interpret things.

What I want to see is the exact rule in the official rules that makes this clear. I'd really like to see how this is worded in the official rules.

Ok, I downloaded the FIDE Laws of Chess and found the appropriate clause:

3.9 The king is said to be 'in check' if it is attacked by one or more of the opponent's pieces, even if such pieces are constrained from moving to that square because they would then leave or place their own king in check. No piece can be moved that will either expose the king of the same colour to check or leave that king in check.

So there is a written rule that specifies this, and I submit that it is a logical fallacy. The "attack" of the King by a piece pinned against its own King should not even exist due to the statement in red, but the statement in bolded black invents a check where it should not exist. I don't know when or why this rule was put into chess.

I will not be implementing this rule in any of my chess variants, and I will have to include a note in the variant's rules the specifically mentions this. Of course none of you care about that, but I wonder how it is that no one has seen this logical fallacy before? Or maybe someone has but the message didn't get through.

[Peter McKillop]

Yes, Harvey, that is how everyone in chess agrees to interpret things.

What I want to see is the exact rule in the official rules that makes this clear. I'd really like to see how this is worded in the official rules.

"Everyone?" Am I not part of "everyone?" I don't agree with your interpretation.

I can only assume that you and Fred are playing the 'hey let's pretend we're stupid and see if we can suck McKillop in' game. Who is stopping you from looking up the official rules by yourself?

[Steve Douglas]

I'm not sure what the official rules explicitly state, but basically:

a) when making a move the king cannot be left in check

b) the king cannot move into check

c) the game ends with checkmate (i.e. the king is in check and no legal move can get the king out of check)

In short, if, after making any otherwise legal move, the king is in check, then the move in question was/is illegal and cannot be played. How is this difficult or illogical?

[Neil Frarey]

I'm not sure what the official rules explicitly state, but basically:

a) when making a move the king cannot be left in check

b) the king cannot move into check

c) the game ends with checkmate (i.e. the king is in check and no legal move can get the king out of check)

In short, if, after making any otherwise legal move, the king is in check, then the move in question was/is illegal and cannot be played. How is this difficult or illogical?

The king doesn't need to be in check for the game to end.

Stalemate is the bane of my bullet chess career ...sigh.

[Steve Douglas]

The king doesn't need to be in check for the game to end.

Stalemate is the bane of my bullet chess career ...sigh.

Yes of course. I was focusing on the check/checkmate aspect of things and misphrased.

Steve

[Egidijus Zeromskis]

In the course of testing a chess variant engine, the following position came up which I will reduce down to the key pieces:

White has Rook on d2, Rook on f1, King on h1.
Black has King on d8, Queen on d5.
It is White's move.

If the last move played was ...Qd5 (from what square it doesn't matter), the move is actually ...Qd5+.

How would you explain to a beginning chess player if he or she tried playing Rf2 instead of Rxd5+? How to explain that Rf2 is illegal?

Is this a logical fallacy in chess?

If it were a White Knight on h1 instead of the King, White could play Rf2 and not worry about the h1 Knight because the Black Queen is pinned.
Yet the White King on h1 is considered to be in check!
This is the logical fallacy.
White's King can be captured.... by an ILLEGAL MOVE.
My engine doesn't think it is check because the Black Queen is pinned. And I tend to agree!

Is there a specific clause in the official rules of chess that covers this? A rule that says something like "the first player to have his or her King captured loses the game"?

There must be, because every chess engine and every chess player will consider the White King to be in check in the given position.

I wonder how drastically things would be changed, maybe even some openings, if White were NOT considered to be in check in positions like this?

Rules

3.9.1	The king is said to be 'in check' if it is attacked by one or more of the opponent's pieces, even if such pieces are constrained from moving to the square occupied by the king because they would then leave or place their own king in check.
3.9.2	No piece can be moved that will either expose the king of the same colour to check or leave that king in check.

Your initial position (learn FEN)



The last moves might have been like
0. Qd3xd5+ Qa8xd5+



The move like 1. Rf2 falls in 3.9.2.
0.... Qxd5+ is good with 3.9.1


***

seems you figured that out too.


***

Your logic is bad. After such moves as 1. Rf2, the black queen captures the white king, and then the white army goes in dust (Rd2 disappears, and Black kings goes nuts in celebration :)

[Pargat Perrer]

"Everyone?" Am I not part of "everyone?" I don't agree with your interpretation.

I can only assume that you and Fred are playing the 'hey let's pretend we're stupid and see if we can suck McKillop in' game. Who is stopping you from looking up the official rules by yourself?

Peter, I am not trying to suck anybody into anything. You wrote about my initial post "Nothing illogical about this" so in fact it is YOU who are making assumptions about "everyone". I see it as illogical, but you decide for me that there is nothing illogical? No, thank you.

In my original position... if White plays Rff2, Black cannot play ...Qe4. Black cannot play ...Qf3. Black cannot play ...Qg2. But lo and behold, there is a King on h1, so Black can play ...Qxh1. That is illogical.

Except that FIDE in their "wisdom" decided to write a specific rule that allows this, which basically makes CAPTURE of the King the ultimate decider of games.

EDIT: I made a mistake in not specifying which White Rook moves to f2, it is the one on the f-file. So the Black Queen is still pinned. Maybe that is part of the misunderstanding.

[Pargat Perrer]

Rules

3.9.1	The king is said to be 'in check' if it is attacked by one or more of the opponent's pieces, even if such pieces are constrained from moving to the square occupied by the king because they would then leave or place their own king in check.
3.9.2	No piece can be moved that will either expose the king of the same colour to check or leave that king in check.

Your initial position (learn FEN)



The last moves might have been like
0. Qd3xd5+ Qa8xd5+



The move like 1. Rf2 falls in 3.9.2.
0.... Qxd5+ is good with 3.9.1


***

seems you figured that out too.


***

Your logic is bad. After such moves as 1. Rf2, the black queen captures the white king, and then the white army goes in dust (Rd2 disappears, and Black kings goes nuts in celebration :)

I just realized that Rf2 is ambiguous, both Rooks can move to f2, but i meant the Rook on the f-file, so that the Black Queen is still pinned. This invokes 3.9.2 in the rules, BUT 3.9.1 is a special clause that was invented to override 3.9.2 in this case and makes the Queen able to capture the King on h1, but not any other White piece on h1. This means that capture of the King is the ultimate decider of games, and if one side captures the king even 1 ply ahead of the other, that player wins.

I think it is FIDE has the bad logic. Why did they invent this special clause? Why is the White King on h1 in check when no other White piece on h1, or on g2, or on f3, or on e4, would be in check?