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Why is, according to Stockfish (depth = 28), Kh8 the best move here for black?

Position from a game between Emanuel Lasker and Wilhelm Steinitz, 1896

This is a position from a game between Emanuel Lasker and Wilhelm Steinitz, 1896.

Nb6 seems to be the natural move in this position. At least to me (an intermediate player).

Yes, there is a check at Qb3 or Bc4. But what's the big deal? The b7 pawn is protected if Nb6 is played. Bc4 is also not an option then.

It's not a machine-like move. Steinitz played this, not in this move, but in the next move. Kh8 is not even among my [an intermediate player :-( ] candidate moves.

This is the first time I am posting in stack exchange. Please excuse the bad formatting of the question. I don't know how to add PGN here so that you guys can go through the game move by move.

  • How did Stockfish score Kh8, f5, and d5 ? (yeah, d5 doesn't look great...) My gut tells me that Stackfish is defusing Qb3 before there's some sort of a pin on the b3-g8 diagonal. – Tony Ennis Nov 19 '15 at 3:04
  • 2
    This is called a prophylactic move – M.M Jul 12 '16 at 2:52
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If you don't play ...Kh8, then for every move you consider making, you're going to have to worry about what happens if White responds Qb3+ or Bc4+. If you're analyzing variations, you always have to take into account that White might play Qb3+ on the fourth move of the sequence or something. This means that

  1. You're going to have to spend extra time on the clock every move checking those checks.

  2. You might mess up and miss one of those times when one of the checks works, and get a disastrous result.

  3. Even if you don't mess up, natural moves that you might want to play might fail due to one of the checks, and you'll have to play a less nice move instead.

  4. When White looks for tactics, he has built-in "hooks" to try to build combinations around. If there's some other weakness in your position at some point, there's a decent chance some double-attack tactics will become possible, for example.

Of course, Stockfish only really cares about the last two, but even that's enough. If you can afford the tempo, it's a really good idea to just get the king out of the way and completely quash all four problems for the whole future of the game.

7

Kh8 is not even among my ... candidate moves

Oh dear!

Kh8 and Kh1 (for white) are automatic moves when the f pawn has moved, sometimes even just before moving the f pawn.

The reason is that often moving the f pawn, apart from creating a weakness, is the precursor to some kind of king side attack. Even if you are not immediately intending a king side attack the weakness on f2/f7 leaves you vulnerable to an annoying Zwischenzug or tactic along the vulnerable diagonal. Moving the king into the corner is going to be needed sooner or later. Therefore it is a useful waiting move before making a more committal move which reveals your intentions.

2

Well there's a threat of Qb3+ winning a pawn. As Black has no counterplay he can't really let that go. Nb6 is possible of course but the knight has no real influence on the c4/d5 squares and a later a4 by White would be awkward. Black's position is already difficult. He needs to get his light-squared bishop onto the h5-e8 diagonal and find a square for his other bishop (f8?) so he can stick the c8 knight on e7 and play for f5 or d5 to free his game. Kh8 is just so he can implement that plan without being hit by an annoying check. I don't know the game, I'm going to look up what actually happened now.

Edit: Hehe, Steinitz played Nb6 and c5 and drew (although lucky to survive on the K-side IMO)

  • Just what I was thinking. Not so sure about the f5 and d5, but maybe at the right moment they could work. – Hockeyfan19 Jul 12 '16 at 10:17
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The reason why the move Kh8 is valuable is because it reduces White's tactical potential.

Black only wants to defend b7 if he has to. So, if White commits to Qb3, then Black will defend the pawn.

Another way to look at it is that Black needs to defend the b-pawn and he has two basic ways to do that: move the king or use a piece to defend the pawn. Moving a piece to defend the pawn is not necessarily useful, but the move Kh8 will always be useful, therefore it is the preferable move.

0

Kh8 has two important functions.

It takes the king off the open white diagonal, where he can be checked by Bc4, or "forked" by Qb3.

It clears the square g8 for Rg8 to defend the g pawn.

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