Answers.Body: <p>It is true that there is only three real assessment of a position, win, draw or loss. What you describe here is endgame tablebases. However it is not possible for today to compute these tablebases for 32 pieces(starting position). </p>
  
  <p>Engine evaluation scores are not nonsense, what they do is using some rules(which also used by humans too) to evaluate positions. And these evaluations guide us to find good moves.</p>
  
  <p>But it is nonsense to interpret engine scores as they are absolute assessments of positions. Or interpret their lines or scores as the <em>best possible</em>, no they are not. </p>
  
  <p>Only way to find truest assessments is to do full enumeration of all possible continuations from a given position. Tablebases do this, engines do not(they generally can't, because of computational limitations)</p>
  
  <p>Engines are just our silicon friends which use our rules(metrics) and lots of memory to evaluate positions with a statistical approach. </p>
  
  <p>Maybe you can check this question, which is quite related: <a href="https://chess.stackexchange.com/questions/13192/how-not-to-use-a-chess-engine/13193#13193">How not to use a chess engine?</a></p>
  
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Answers.Body: <p>If you only know about W,L,D you usually don't have a clue about what the best move is. Or to put it differently: Against a competent player you will never get a move with (D,W) because in all positions you will only randomly choose among (D,D) and that's no way to exert any pressure. Your "theoretical supercomputer" will have trouble beating a 1500. </p>
  
  <p>Knowing the fastest way to mate also only allows you to choose the best move when you are already winning, you need some kind of additional heuristic to get there. You could try to minimise the number of drawing moves that your opponent will have, but that already entails a tree search and is not much different from what engines do today. (And possibly less effective.)</p>
  
  <p>You are basically saying that the concept of strong or weak play is meaningless. But that is not true. It can be measured objectively in different ways like Elo or intrinsic performance rating. There is an objective difference in quality between two moves, even if they lead to the same outcome after optimal further play. </p>
  
  <p>Your observation that moves can in theory be classified in such a way is correct of course, but also completely useless. Such a rough way to assess positions is not enough to take good decisions. You can use the same empty reasoning on other problems as well, and the result will generally be just as useless. </p>
  
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Answers.Text: Having 32-men Tablebases, one can easily write an algorithm to select the move with response which is hardest to find, to exert pressure. Say, White has two possible moves, move A, and move B. After move A, Black has 3 drawing options, and after move B Black has 1 drawing option. Then we can say move B is *stronger*, exerting more pressure as it's harder to find a solution.
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Answers.Text: It might be the case however, that after that one drawing option for Black, White only has moves that put very little pressure on black, whereas after the three drawing moves by Black, White always has an option that keeps the pressure up. So, to actually minimise Black's options over the next X moves you have to do a tree search, like a mentioned in my answer ….
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Answers.Text: And generally minimising your opponents good choices is not a terribly impressive strategy: It only leads to forcing moves not to good moves.
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Answers.Text: This answer understates the power of perfect knowledge ("32-piece tablebases"). And without defining what is meant by "pressure", a lot of the assertions are empty. The implication that a 1500-rated player will hardly ever make a `(D,L)` move (giving the theoretically-perfect opponent the win) is almost *certainly* false. Considering that even the very top human *and* computer players do in fact *lose* games. (I.e. even at the very top limits, no player, even computers, makes all `(D,D)` moves.)
Answers.UserDisplayName: Jeff Y
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Answers.Text: Also, just consider what the Elo of this theoretically-perfect player would be. Since it never loses any game (worst it can do is draw, presuming Chess at the starting position is a theoretical draw) against any opponent, its Elo will be *at minimum* the top Elo of all other players. Which completely contradicts the implication that such an entity does not play "strongly" (because Elo is invoked as an objective measure of strength in this answer).
Answers.UserDisplayName: Jeff Y
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Answers.Text: That's just completely wrong. It will only reach the top of all players if it plays against Carlsen and Carlsen only. If it just participates in normal Swiss tournaments I'm positive it would struggle to reach 2000 because every halfway decent player will easily draw against it.
Answers.UserDisplayName: BlindKungFuMaster
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Answers.Text: It is simply untrue that "every halfway decent player" can easily avoid `(D,L)` moves, since *every* player, even Carlsen, in fact *loses* some games even against imperfect players. See above.
Answers.UserDisplayName: Jeff Y
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Answers.Text: Yes, people do lose, if confronted with strong moves. But it is much easier to avoid blunders if you are only confronted with random non-losing moves. Your 32-tablebase will not attack, it will not create threats, it won't even avoid weaknesses in its position, as long as they are not lethal, it will only avoid losing, that's just not the way to beat good players.
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Answers.Text: The 32-tablebase will attack and create threats at the very least randomly, and up to certainly in cases where the attack or threat is the only non-losing move. It is simply false to say "will not".
Answers.UserDisplayName: Jeff Y
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Answers.Text: But we're sort of arguing in an empirical vacuum as to 32-piece, since there is no such player. But there is certainly data to be had: it would be very interesting to examine the 7-piece (or fewer) theoretical-draw play of grandmasters in reference to today's available endgame tablebases... Perhaps someone will.
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Answers.Text: One could simulate such a player by using a very strong engine and choosing a random move better than -1.00. Analysing GM play in 7-piece position strikes me as useless. This discussion is all about playing against random non-losing moves, all these GM-games were played against purposeful opponents.
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Answers.Text: 1) comparing even "very strong engine" against "32-tablebase" is practically useless as well (see the "non-determinative" comment in my answer above); 2) but even presuming a -1.00 score can approximate "theoretical draw", you'd have to include a "theoretical win" boundary as well, say +5.00(?), to be fair: only if no move evaluates at or above +5.00, then choose randomly from all moves at or above -1.00 score, otherwise pick top-evaluating move.
Answers.UserDisplayName: Jeff Y
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Answers.Text: Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/34484/discussion-between-blindkungfumaster-and-jeff-y).
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Answers.Body: <p>You are somewhat correct. In theory, each position can be correctly categorized in one of three ways -- win for the side to move, loss for the side to move, draw, <strong>all presuming "best play" by both sides from that position</strong>. That last caveat is required to make the ideas of "will win", "will lose", and "will draw" well-defined. But that caveat <strong>also</strong> means that the side to move can never <strong>improve</strong> on the position categorization, because that categorization already presumes (prices-in) that the side to move will make its <strong>best</strong> move. So the only possibilities for <strong>move</strong> categorizations are: <code>(W,W), (W,D), (W,L), (D,D), (D,L), (L,L)</code>. I.e. six instead of nine. The side to move can only hold or worsen (blunder) its theoretical value, in other words.</p>
  
  <p>As for severity of error, presumably <code>(W,L)</code> is worse than <code>(W,D)</code>, but other than that, blunder is blunder, yes (<code>(W,D), (D,L)</code>). And any move that maintains value is a theoretical non-blunder, yes (<code>(W,W), (D,D), (L,L)</code>).</p>
  
  <p>As to engine scores, they are in most cases theoretically "meaningless" I suppose, as above, but not objectively so. They could be considered to be trying to estimate the probability that the theoretical value is closer to W, D, or L, on some scale, given the data they have been able to glean so far in their forward position search. And sometimes they do produce theoretical values (forced-mate detections). But I've also got to think that the error-bars on non-theoretical engine values are also pretty large, meaning that we're talking about estimates of estimates of probabilities, which is pretty, well, non-definitive...</p>
  
  <p>Also, see Saibot's answer regarding so-called Tablebases. Chess has been solved theoretically for all positions with 7 or fewer pieces on the board (two kings plus up to any five pieces). Here is an online resource for most of the 6-piece tablebases: <a href="http://www.k4it.de/?topic=egtb&amp;lang=en" rel="nofollow">http://www.k4it.de/?topic=egtb&amp;lang=en</a></p>
  
  <p>Another wrinkle on theoretical categorizations is "distance to mate" for W and L positions. Presumably a win in fewer moves is theoretically "better", so a <code>(W,W)</code> move that doesn't reduce "distance to mate" could be considered a "blunder" as well, as could a <code>(L,L)</code> move that shortens "distance to mate".</p>
  
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Body: <p>Since chess is finite and deterministic, it is theoretically possible to objectively label any position as winning, losing, or drawn. For example, it seems very likely that the starting position is drawn.</p>
  
  <p>Therefore, the current system of "score" that engines use to analyze a position is actually nonsense from an objective point of view. With enough depth, the "score" would always be +100 (or whatever the engine uses for forced checkmate for white), 0 (drawn), or -100 (forced checkmate for black). Are these not the <em>only</em> possible evaluations of a position?</p>
  
  <p>If so, it follows that moves can be characterized in exactly 9 ways. If W, L, D represent won, lost, and drawn positions, the nine possibilities can simply be written as ordered pairs of game states before and after the move. </p>
  
  <p>For example, a move that makes a won position into a drawn won could be (W,D).</p>
  
  <p>Our intuition of a range of severity for mistakes is something that a theoretical supercomputer would not share. Is it then meaningless to speak of how bad a mistake is? It seems to me that the only relevant point is whether it changes if the game is objectively won/lost/drawn.</p>
  
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Comments.Text: In theory, there's no difference between theory and practice. In practice, there is.
Comments.UserDisplayName: Pete Becker
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Comments.Text: The problem is that the status of a chess position is not known (except for positions with a few men where endgame databases exist, or for forced mates not too far away for brute force calculation)
Comments.UserDisplayName: Sir Cornflakes
Tags: <computer-chess>
Title: Theoretically, shouldn't analysis of any chess move have exactly nine possibilities?
ThreadText: # Theoretically, shouldn't analysis of any chess move have exactly nine possibilities?
  
  (Asked by: username_0 on 2016-01-15)
  
  Since chess is finite and deterministic, it is theoretically possible to objectively label any position as winning, losing, or drawn. For example, it seems very likely that the starting position is drawn.
  
  Therefore, the current system of "score" that engines use to analyze a position is actually nonsense from an objective point of view. With enough depth, the "score" would always be +100 (or whatever the engine uses for forced checkmate for white), 0 (drawn), or -100 (forced checkmate for black). Are these not the *only* possible evaluations of a position?
  
  If so, it follows that moves can be characterized in exactly 9 ways. If W, L, D represent won, lost, and drawn positions, the nine possibilities can simply be written as ordered pairs of game states before and after the move.
  
  For example, a move that makes a won position into a drawn won could be (W,D).
  
  Our intuition of a range of severity for mistakes is something that a theoretical supercomputer would not share. Is it then meaningless to speak of how bad a mistake is? It seems to me that the only relevant point is whether it changes if the game is objectively won/lost/drawn.
  
  **Tags:** computer-chess
  
  > **Comments:**
  > **username_1**: In theory, there's no difference between theory and practice. In practice, there is.  
  > **username_2**: The problem is that the status of a chess position is not known (except for positions with a few men where endgame databases exist, or for forced mates not too far away for brute force calculation)  
  
  ---
  
  ## 3 answers
  
  ### Answer by username_5 on 2016-01-15. Score: 7 | Accepted answer
  
  You are somewhat correct. In theory, each position can be correctly categorized in one of three ways -- win for the side to move, loss for the side to move, draw, **all presuming "best play" by both sides from that position**. That last caveat is required to make the ideas of "will win", "will lose", and "will draw" well-defined. But that caveat **also** means that the side to move can never **improve** on the position categorization, because that categorization already presumes (prices-in) that the side to move will make its **best** move. So the only possibilities for **move** categorizations are: `(W,W), (W,D), (W,L), (D,D), (D,L), (L,L)`. I.e. six instead of nine. The side to move can only hold or worsen (blunder) its theoretical value, in other words.
  
  As for severity of error, presumably `(W,L)` is worse than `(W,D)`, but other than that, blunder is blunder, yes (`(W,D), (D,L)`). And any move that maintains value is a theoretical non-blunder, yes (`(W,W), (D,D), (L,L)`).
  
  As to engine scores, they are in most cases theoretically "meaningless" I suppose, as above, but not objectively so. They could be considered to be trying to estimate the probability that the theoretical value is closer to W, D, or L, on some scale, given the data they have been able to glean so far in their forward position search. And sometimes they do produce theoretical values (forced-mate detections). But I've also got to think that the error-bars on non-theoretical engine values are also pretty large, meaning that we're talking about estimates of estimates of probabilities, which is pretty, well, non-definitive...
  
  Also, see Saibot's answer regarding so-called Tablebases. Chess has been solved theoretically for all positions with 7 or fewer pieces on the board (two kings plus up to any five pieces). Here is an online resource for most of the 6-piece tablebases: [http://www.k4it.de/?topic=egtb⟨=en](http://www.k4it.de/?topic=egtb&lang=en)
  
  Another wrinkle on theoretical categorizations is "distance to mate" for W and L positions. Presumably a win in fewer moves is theoretically "better", so a `(W,W)` move that doesn't reduce "distance to mate" could be considered a "blunder" as well, as could a `(L,L)` move that shortens "distance to mate".
  
  
  ---
  
  ### Answer by username_3 on 2016-01-15. Score: 4
  
  It is true that there is only three real assessment of a position, win, draw or loss. What you describe here is endgame tablebases. However it is not possible for today to compute these tablebases for 32 pieces(starting position).
  
  Engine evaluation scores are not nonsense, what they do is using some rules(which also used by humans too) to evaluate positions. And these evaluations guide us to find good moves.
  
  But it is nonsense to interpret engine scores as they are absolute assessments of positions. Or interpret their lines or scores as the *best possible*, no they are not.
  
  Only way to find truest assessments is to do full enumeration of all possible continuations from a given position. Tablebases do this, engines do not(they generally can't, because of computational limitations)
  
  Engines are just our silicon friends which use our rules(metrics) and lots of memory to evaluate positions with a statistical approach.
  
  Maybe you can check this question, which is quite related: [How not to use a chess engine?](https://chess.stackexchange.com/questions/13192/how-not-to-use-a-chess-engine/13193#13193)
  
  
  ---
  
  ### Answer by username_4 on 2016-01-16. Score: -1
  
  If you only know about W,L,D you usually don't have a clue about what the best move is. Or to put it differently: Against a competent player you will never get a move with (D,W) because in all positions you will only randomly choose among (D,D) and that's no way to exert any pressure. Your "theoretical supercomputer" will have trouble beating a 1500.
  
  Knowing the fastest way to mate also only allows you to choose the best move when you are already winning, you need some kind of additional heuristic to get there. You could try to minimise the number of drawing moves that your opponent will have, but that already entails a tree search and is not much different from what engines do today. (And possibly less effective.)
  
  You are basically saying that the concept of strong or weak play is meaningless. But that is not true. It can be measured objectively in different ways like Elo or intrinsic performance rating. There is an objective difference in quality between two moves, even if they lead to the same outcome after optimal further play.
  
  Your observation that moves can in theory be classified in such a way is correct of course, but also completely useless. Such a rough way to assess positions is not enough to take good decisions. You can use the same empty reasoning on other problems as well, and the result will generally be just as useless.
  
  > **Comments:**
  > **username_3**: Having 32-men Tablebases, one can easily write an algorithm to select the move with response which is hardest to find, to exert pressure. Say, White has two possible moves, move A, and move B. After move A, Black has 3 drawing options, and after move B Black has 1 drawing option. Then we can say move B is *stronger*, exerting more pressure as it's harder to find a solution.  
  > **username_4**: It might be the case however, that after that one drawing option for Black, White only has moves that put very little pressure on black, whereas after the three drawing moves by Black, White always has an option that keeps the pressure up. So, to actually minimise Black's options over the next X moves you have to do a tree search, like a mentioned in my answer ….  
  > **username_4**: And generally minimising your opponents good choices is not a terribly impressive strategy: It only leads to forcing moves not to good moves.  
  > **username_5**: This answer understates the power of perfect knowledge ("32-piece tablebases"). And without defining what is meant by "pressure", a lot of the assertions are empty. The implication that a 1500-rated player will hardly ever make a `(D,L)` move (giving the theoretically-perfect opponent the win) is almost *certainly* false. Considering that even the very top human *and* computer players do in fact *lose* games. (I.e. even at the very top limits, no player, even computers, makes all `(D,D)` moves.)  
  > **username_5**: Also, just consider what the Elo of this theoretically-perfect player would be. Since it never loses any game (worst it can do is draw, presuming Chess at the starting position is a theoretical draw) against any opponent, its Elo will be *at minimum* the top Elo of all other players. Which completely contradicts the implication that such an entity does not play "strongly" (because Elo is invoked as an objective measure of strength in this answer).  
  > **username_4**: That's just completely wrong. It will only reach the top of all players if it plays against Carlsen and Carlsen only. If it just participates in normal Swiss tournaments I'm positive it would struggle to reach 2000 because every halfway decent player will easily draw against it.  
  > **username_5**: It is simply untrue that "every halfway decent player" can easily avoid `(D,L)` moves, since *every* player, even Carlsen, in fact *loses* some games even against imperfect players. See above.  
  > **username_4**: Yes, people do lose, if confronted with strong moves. But it is much easier to avoid blunders if you are only confronted with random non-losing moves. Your 32-tablebase will not attack, it will not create threats, it won't even avoid weaknesses in its position, as long as they are not lethal, it will only avoid losing, that's just not the way to beat good players.  
  > **username_5**: The 32-tablebase will attack and create threats at the very least randomly, and up to certainly in cases where the attack or threat is the only non-losing move. It is simply false to say "will not".  
  > **username_5**: But we're sort of arguing in an empirical vacuum as to 32-piece, since there is no such player. But there is certainly data to be had: it would be very interesting to examine the 7-piece (or fewer) theoretical-draw play of grandmasters in reference to today's available endgame tablebases... Perhaps someone will.  
  > **username_4**: One could simulate such a player by using a very strong engine and choosing a random move better than -1.00. Analysing GM play in 7-piece position strikes me as useless. This discussion is all about playing against random non-losing moves, all these GM-games were played against purposeful opponents.  
  > **username_5**: 1) comparing even "very strong engine" against "32-tablebase" is practically useless as well (see the "non-determinative" comment in my answer above); 2) but even presuming a -1.00 score can approximate "theoretical draw", you'd have to include a "theoretical win" boundary as well, say +5.00(?), to be fair: only if no move evaluates at or above +5.00, then choose randomly from all moves at or above -1.00 score, otherwise pick top-evaluating move.  
  > **username_4**: Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/34484/discussion-between-blindkungfumaster-and-jeff-y).  
  
  ---
  
  