Answers.Body: <p>Sure, examples exist. E.g. <a href="https://en.wikipedia.org/wiki/World_Chess_Championship_2018#Game_6:_Carlsen%E2%80%93Caruana,_%C2%BD%E2%80%93%C2%BD" rel="noreferrer">Game 6 of Carlsen-Caruana</a>, World Chess Championship 2018:</p>
  
  <pre><code>[FEN "5k2/8/5pK1/3B1P1P/3n4/8/3b4/8 w - - 6 67"]
  </code></pre>
  
  <ol start="67">
  <li>Kg6? loses, but no human would have found the refutation.</li>
  </ol>
  
  <p>As for games where the exact losing move cannot be found even by the best current engines - I spoke to a correspondence chess expert recently, and I'm confident they don't exist. Given a decisive game, an expert correspondence chess player will always be able to find the losing move, but it will not be trivial, and a lot of analysis is required.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-02-21T17:19:00.437Z
Answers.Text: Nice example. But just to check I'm getting you right, how could a correspondence chess expert find that 67.Kg6 loses if, as Kasparov famously said, "no human would have found the refutation"?
Answers.UserDisplayName: exp8j
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-02-21T20:48:05.473Z
Answers.Text: @exp8j they use engine assistance.
Answers.UserDisplayName: Allure
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-02-21T00:46:52.387Z
Answers.LastActivityDate: 2020-02-21T00:46:52.387Z
Answers.UserDisplayName: Allure
Answers.Body: <p>Yes, but...
  Nobody will agree on all of  them.</p>
  
  <p>If two PERFECT computers played you could not tell the losing move or else it would be the first move. But I suspect a perfect game would be a draw.</p>
  
  <p>The reason why moving loses is a myth is that the game is played by imperfect humans.</p>
  
  <p>THE losing move is the next to last mistake.  But what if a mistake confuses the opponent who resigns.  What if the so called losing move wins this time but loses against another player in another game.</p>
  
  <p>Except for the grossest of blunders it will be next to impossible to declare ONE move as THE losing move. </p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-02-20T17:41:11.127Z
Answers.Text: I think that in a given position, a given move belongs in one, and only one, of the 3 cases: winning, losing, or drawing; of course assuming best play from both sides, and also assuming that chess is a finite game (by the 50 moves rule). So in every non-drawn game, the exact losing move is very well-defined, although possibly very difficult to find.
Answers.UserDisplayName: exp8j
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Answers.Text: I think that since we are not perfect nor are the computers that moves belong in a probability range just like quantum particles because we cannot know exactly what where they are nor how fast.
Answers.UserDisplayName: edwina oliver
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-02-20T18:23:51.703Z
Answers.Text: I think that future computers will completely solve chess out. But this will not diminish the fascination it exerts on us! Time-limits aside, computers cannot *interpret* the unfolding of moves and plans like humans do, who value the aesthetics of chess and can embed its patterns in a complex of innumerable psychological associations.
Answers.UserDisplayName: exp8j
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-02-20T19:06:03.550Z
Answers.Text: Maybe.  I doubt it will be in our lifetime.  There are just too many possible moves from start to finish if you look at every variation.  And if you dont look at every one you could get it wrong.
Answers.UserDisplayName: edwina oliver
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Answers.LastActivityDate: 2020-02-20T15:05:43.533Z
Answers.UserDisplayName: edwina oliver
Body: <p>Are there examples of chess games where the exact losing move has been found only with the help of engines?</p>
  
  <p>Better still, games where the exact losing move cannot be found even by the best current engines?</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-02-20T14:20:14.740Z
Comments.Text: Good question. I'm sure I remember, back before the days of engines, seeing annotated games of top positional players like Karpov, or Ulf Anderson, where the opponent's position just slowly rotted until it fell apart with no apart single move being the cause.
Comments.UserDisplayName: Brian Towers
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-02-20T15:45:02.910Z
Comments.Text: Most games between strong players, it really is not one move, unless it is a blunder...it is an accumulation of small errors, and they lead to a final error.
Comments.UserDisplayName: PhishMaster
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-02-20T17:57:53.887Z
Comments.Text: @PhishMaster: I think you will agree that in every non-drawn game there is one, and only one, move that is *the* losing move, assuming best play in the sequel. This holds in theory, as chess is a finite game, but in practice it may seem like an accumulation of small errors, as the exact losing move can be extremely difficult to find.
Comments.UserDisplayName: exp8j
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-02-20T18:08:20.770Z
Comments.Text: @exp8j I do not think that at all.
Comments.UserDisplayName: PhishMaster
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-02-21T20:50:55.490Z
Comments.Text: @exp8j if I blunder, then you blunder back, and then I blunder again, I've made two losing moves.
Comments.UserDisplayName: Allure
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-02-22T15:50:07.800Z
Comments.Text: @ Allure  We want to find the first losing move, *not to analyze the entire game*. It's a well-defined but very difficult problem,  starting from the first move!  E.g. 1.e4  is or is not a losing move? We may assume not, and proceed examining a specific game until we arrive at a suspicious one, e.g. 17.g4, where we or the engines can decide. If it's found losing, then certainly *the* losing move lies in the range 1-17, and with better future engines or human analyzers this interval could be narrowed down.
Comments.UserDisplayName: exp8j
Tags: <engines><calculation><famous-games>
Title: The difficulty of finding the exact losing move
ThreadText: # The difficulty of finding the exact losing move
  
  (Asked by: username_0 on 2020-02-20)
  
  Are there examples of chess games where the exact losing move has been found only with the help of engines?
  
  Better still, games where the exact losing move cannot be found even by the best current engines?
  
  **Tags:** engines, calculation, famous-games
  
  > **Comments:**
  > **username_1**: Good question. I'm sure I remember, back before the days of engines, seeing annotated games of top positional players like Karpov, or Ulf Anderson, where the opponent's position just slowly rotted until it fell apart with no apart single move being the cause.  
  > **username_2**: Most games between strong players, it really is not one move, unless it is a blunder...it is an accumulation of small errors, and they lead to a final error.  
  > **username_0**: @username_2: I think you will agree that in every non-drawn game there is one, and only one, move that is *the* losing move, assuming best play in the sequel. This holds in theory, as chess is a finite game, but in practice it may seem like an accumulation of small errors, as the exact losing move can be extremely difficult to find.  
  > **username_2**: @username_0 I do not think that at all.  
  > **username_3**: @username_0 if I blunder, then you blunder back, and then I blunder again, I've made two losing moves.  
  > **username_0**: @ username_3  We want to find the first losing move, *not to analyze the entire game*. It's a well-defined but very difficult problem,  starting from the first move!  E.g. 1.e4  is or is not a losing move? We may assume not, and proceed examining a specific game until we arrive at a suspicious one, e.g. 17.g4, where we or the engines can decide. If it's found losing, then certainly *the* losing move lies in the range 1-17, and with better future engines or human analyzers this interval could be narrowed down.  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_3 on 2020-02-21. Score: 5
  
  Sure, examples exist. E.g. [Game 6 of Carlsen-Caruana](https://en.wikipedia.org/wiki/World_Chess_Championship_2018#Game_6:_Carlsen%E2%80%93Caruana,_%C2%BD%E2%80%93%C2%BD), World Chess Championship 2018:
  
  ```
  [FEN "5k2/8/5pK1/3B1P1P/3n4/8/3b4/8 w - - 6 67"]
  
  ```
  
  67. Kg6? loses, but no human would have found the refutation.
  
  As for games where the exact losing move cannot be found even by the best current engines - I spoke to a correspondence chess expert recently, and I'm confident they don't exist. Given a decisive game, an expert correspondence chess player will always be able to find the losing move, but it will not be trivial, and a lot of analysis is required.
  
  > **Comments:**
  > **username_0**: Nice example. But just to check I'm getting you right, how could a correspondence chess expert find that 67.Kg6 loses if, as Kasparov famously said, "no human would have found the refutation"?  
  > **username_3**: @username_0 they use engine assistance.  
  
  ---
  
  ### Answer by username_4 on 2020-02-20. Score: 0
  
  Yes, but...
  Nobody will agree on all of them.
  
  If two PERFECT computers played you could not tell the losing move or else it would be the first move. But I suspect a perfect game would be a draw.
  
  The reason why moving loses is a myth is that the game is played by imperfect humans.
  
  THE losing move is the next to last mistake. But what if a mistake confuses the opponent who resigns. What if the so called losing move wins this time but loses against another player in another game.
  
  Except for the grossest of blunders it will be next to impossible to declare ONE move as THE losing move.
  
  > **Comments:**
  > **username_0**: I think that in a given position, a given move belongs in one, and only one, of the 3 cases: winning, losing, or drawing; of course assuming best play from both sides, and also assuming that chess is a finite game (by the 50 moves rule). So in every non-drawn game, the exact losing move is very well-defined, although possibly very difficult to find.  
  > **username_4**: I think that since we are not perfect nor are the computers that moves belong in a probability range just like quantum particles because we cannot know exactly what where they are nor how fast.  
  > **username_0**: I think that future computers will completely solve chess out. But this will not diminish the fascination it exerts on us! Time-limits aside, computers cannot *interpret* the unfolding of moves and plans like humans do, who value the aesthetics of chess and can embed its patterns in a complex of innumerable psychological associations.  
  > **username_4**: Maybe.  I doubt it will be in our lifetime.  There are just too many possible moves from start to finish if you look at every variation.  And if you dont look at every one you could get it wrong.  
  
  ---
  
  