Answers.Body: <blockquote>
  <p>Why do chess puzzles need a unique solution?</p>
  </blockquote>
  <p>Because those are the rules. The governing body, the <a href="https://www.wfcc.ch/wfcc-about/hcc/" rel="noreferrer">World Federation of Chess Composition</a>, sets the rules. Their latest <a href="http://www.sci.fi/%7Estniekat/books/hcc8.pdf" rel="noreferrer">Handbook of Chess Composition</a> includes a Codex where the rules are laid out.</p>
  <p>Here are the relevant articles:</p>
  <blockquote>
  <p><strong>Article 8 - Author's Solution</strong></p>
  <p>Every chess composition must be capable of being solved only by the author's solution. Special features of the author's solution (such as multiple solutions or setplay in helpplay problems) should be expressly stipulated.</p>
  <p><strong>Article 9 - Cook</strong></p>
  <p>A chess composition is called cooked if it has a solution that differs in its first move from the author's solution.</p>
  <p><strong>Article 10 - Dual</strong></p>
  <p>A dual is said to occur if, after the first move, there is more than one method of satisfying the stipulation.</p>
  </blockquote>
  
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Answers.Text: So a puzzle with multiple solutions could be turned into a dual just by introducing a forced first move?
Answers.UserDisplayName: qwr
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Answers.Text: Hmm, don't get me wrong, this is a great answer, but it must be pointed out that the rules you mention only apply to those who wish to follow to them... There is no constraint on web sites, tournaments, nay, on no one at all that don't wish to adhere.
Answers.UserDisplayName: LoremIpsum
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Answers.Text: Sigh, this answer might cause folk to mistakenly take you for a jobsworth, Brian :)
  "Them's the park regulations! No ball games!" said the park officer blowing his whistle.
  Unless there was an underlying motivation, it wouldn't be a convention. (And these aren't rules btw.)
Answers.UserDisplayName: Laska
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Answers.Text: It might be helpful to clarify whether a "dual" occurs in a white-to-move puzzle where the black might respond in multiple ways to various moves, but for each move there would only be one follow-up by white that would solve the puzzle, or in those where some responses by black might would allow only one correct line by white, but others would allow the puzzle to be solved multiple ways (e.g. in a mate-in-4 puzzle, a possible black response to the key move would allow immediate checkmate, but white could also waste a tempo and still checkmate black in the stipulated four moves).
Answers.UserDisplayName: supercat
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Answers.Text: All else being equal, a puzzle that requires perfect play on all lines may be more elegant than one that would allow imperfect play on some, but all else isn't always equal.  Adding complexity to a position to make any imperfections fatal in all cases may make a puzzle less elegant than it would be if imperfect play were allowed on some "easy" lines.
Answers.UserDisplayName: supercat
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Answers.Text: @supercat: I would say that there are at least three different possible interpretations of "Black might respond in multiple ways." You could simply require that Black only has one legal move, but that will be rare even in artificially constructed positions, so that's probably not a good restriction to have on a puzzle. You could say that Black must have one move that does not lead to immediate forced mate, but that is still rather restrictive. Or you could say that Black must have one "good" move with all others "obviously wrong," but that is subjective.
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Answers.UserDisplayName: Brian Towers
Answers.Body: <p>I'll have to disagree with the premise here. They don't need a unique solution.</p>
  <p>For a matter of fact, some Chesstempo tatic puzzles have sub-optimal solutions, but if they still reach a treshhold evaluation (+-1.5 if I recall correctly) you won't fail or pass the puzzle; Instead a blue box will tell you that although that is a winning move, you should keep trying finding the best one.</p>
  
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Answers.CreationDate: 2022-09-30T09:02:57.940Z
Answers.Text: Thanks for the chesstempo tip - probably a good tool for training! 
  Corresponding your side note: there are many such situations. Consider a case where there are two ideas that might work and if candidate move 2 (/idea 2) works, then another (third) move would also work (e.g. Queen on the same diagonal). You can instantly exclude that candidate.
Answers.UserDisplayName: Hauptideal
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Answers.Text: @Hauptideal Ah, very true, I was only thinking about it from immediately the initial move perspective. I then remove the sidenote.
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Answers.UserDisplayName: LoremIpsum
Answers.Body: <p>Don't look at chess puzzles as a way of training for competitive chess. Chess problems are a genre of their own. A good chess problem is a piece of art.</p>
  <p>By requiring a unique solution we place an extra constraint on the puzzle, making it more valuable. This constraint makes it even more difficult to craft a nice puzzle, and we appreciate that.</p>
  <p>See <a href="https://sportstar.thehindu.com/magazine/chess-problem-an-art-form/article29710563.ece" rel="noreferrer">https://sportstar.thehindu.com/magazine/chess-problem-an-art-form/article29710563.ece</a></p>
  
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Answers.UserDisplayName: g.kertesz
Answers.Body: <p>Basically for the same reason that we're not impressed by a win by
  queen sacrifice if there was also a pedestrian one- or two-move mate.</p>
  <p>There <em>are</em> chess problems that deliberately have more than one solution,
  often to complement each other in some way.  This usually happens in helpmates
  (which are probably of little or no interest to players seeking &quot;training&quot;)
  but they're occasionally seen also in direct-mate problems.</p>
  
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Answers.UserDisplayName: Noam D. Elkies
Answers.Body: <p>I can think of one puzzle that doesn't and can't have a unique solution, but which of the two possible solutions is correct and which is wrong depends on information that can't be derived from the board itself. It's from Smullyan's &quot;Chess Mysteries of Sherlock Holmes&quot; the chapter &quot;Thoughts of a Logician&quot;, so I guess it falls under</p>
  <blockquote>
  <p>Article 8 - Author's Solution</p>
  <p>Every chess composition must be capable of being solved only by the author's solution. <strong>Special features of the author's solution (such as multiple solutions or setplay in helpplay problems) should be expressly stipulated.</strong></p>
  </blockquote>
  
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Answers.CreationDate: 2022-09-30T14:44:25.563Z
Answers.Text: Welcome to [chess.se] and thanks for your answer. Could you [edit] your answer to provide more details of the puzzle? I feel that would make it better.
Answers.UserDisplayName: Glorfindel
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Answers.Text: This is a common RPA puzzle (with the interdependence of two white castlings), which Holmes solves using the RS method. The puzzle is not unique. There are a lot of them. It is because of them that the Rules have prioritized PRA over RS. There are no other reasons for the priority of the PRA.
Answers.UserDisplayName: Элси Ринген
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Answers.UserDisplayName: t.gruen
Answers.Body: <p>Puzzles are usually intended to be hard or at least challenging. Puzzles with multiple solutions tend to be easier since one can arrive at one though multiple avenues. People who design or choose to present puzzles  don't want puzzles that are trivial. So the result is that most tend to have one unique solution.</p>
  
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Answers.CreationDate: 2022-09-30T14:00:47.287Z
Answers.Text: Actually, it makes puzzles easier. Knowing more relevant features of a problem makes it easier to solve and this is no exception.
Answers.UserDisplayName: Hauptideal
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-10-02T19:17:56.800Z
Answers.Text: Imagine being in the middle of a labyrinth. Would it be more difficult if there were multiple paths leading home?
Answers.UserDisplayName: Hunaphu
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Answers.Text: @Hunaphu the analogy isn't really fitting. But to answer this using your analogy: Yes! It can be more difficult if you have extra knowledge about the paths when there is only one correct path. E.g. if you have three candidates, but know that two paths merge later, you instantaneously know the right path without any difficulty. The knowledge that there is only one path leading home made it much easier to find in that case, because the others could be excluded so quickly.
Answers.UserDisplayName: Hauptideal
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Answers.UserDisplayName: stackoverblown
Answers.Body: <p>If someone says to me: &quot;Let's meet at (mumble) on (mumble)&quot;, I may respond: &quot;Sorry I didn't catch that.&quot;</p>
  <p>Tactical puzzles and artistic problems are both (in different ways) about communicating a message, and if the solution is not essentially unique, then the message is unclear.</p>
  <p>Uniqueness then becomes a thing in its own right. In a puzzle, it can simplify the automated response, which can just focus on a single line. In a problem, it becomes an aesthetic property: how wonderfully unlikely in a certain position that the correct sequence of moves is unique!</p>
  <p>It's perfectly valid (and fun!) to use the property of uniqueness to prune the search space when solving. Solving is a way to learn and appreciate, and difficulty of solving may be a virtue in both puzzle and problem. However this difficulty is subordinate to the nature of the solution. I can legitimately profit (although less) from a puzzle/problem by just reading the solution.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-09-30T07:44:52.647Z
Answers.Text: Straight up to the point, and to the OP: Chess puzzles =!= Chess problems. Although, getting no points for a perfect alternative solution to a chess *puzzle* is also annoying. Which is the reason tactics puzzles better have only one solution, either. Naturally, positional-play oriented puzzles would even be "worse" in this regard.
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Answers.Text: @LoremIpsum maybe you are joking :) but my little idea here is that there is a significant difference between e.g. "5pm on Sunday" and "9pm on Monday", and if someone is trying to schedule a meeting with me, it's important that I hear their message clearly
Answers.UserDisplayName: Laska
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Answers.LastEditDate: 2022-10-05T06:08:18.877Z
Answers.UserDisplayName: Laska
Body: <p>Why do chess puzzles need a unique solution?
  This is different from real games, where such situations do occur, but more frequently, there are multiple avenues to success. Contrary to what one might think, that makes chess puzzles <strong>easier</strong>, not harder! I have solved countless puzzles only because I knew that there is one and only one solution and therefore could exclude moves that I would have needed to consider in a real game.</p>
  <p>Especially in some cases, where there are multiple different mates, all solutions should be accepted. Adding such puzzles in a set would lead to better and more realistic training.
  Also, practical positions may be added where the task may be to play until a certain evaluation threshold is reached or held for a certain number of moves against an engine.
  Why is tactical training today so &quot;unrealistic&quot;?</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2022-10-01T15:32:52.793Z
Comments.Text: In many sports it is common to do practice drills that focus on a particular skill in that sport but don't directly translate to how you would do it in an actual game.  Eg in American football the kicker does practice kicks that warm up the kicking motion but it's still very different from when trying to kick with an opposing team is rushing down on you and the ball positioning / snap is suboptimal. With euro football you might do passing drills etc, but then also do full scrimmages (practice game) because both aspects are useful.
Comments.UserDisplayName: eps
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2022-10-01T21:25:18.117Z
Comments.Text: They don't. Some chess puzzles might have unique solutions. Others have several and some might have many solutions.
Comments.UserDisplayName: Robbie Goodwin
Tags: <problems><tactics><training><puzzles>
Title: Why do chess puzzles need a unique solution?
ThreadText: # Why do chess puzzles need a unique solution?
  
  (Asked by: username_0 on 2022-09-29)
  
  Why do chess puzzles need a unique solution?
  This is different from real games, where such situations do occur, but more frequently, there are multiple avenues to success. Contrary to what one might think, that makes chess puzzles **easier**, not harder! I have solved countless puzzles only because I knew that there is one and only one solution and therefore could exclude moves that I would have needed to consider in a real game.
  
  Especially in some cases, where there are multiple different mates, all solutions should be accepted. Adding such puzzles in a set would lead to better and more realistic training.
  Also, practical positions may be added where the task may be to play until a certain evaluation threshold is reached or held for a certain number of moves against an engine.
  Why is tactical training today so "unrealistic"?
  
  **Tags:** problems, tactics, training, puzzles
  
  > **Comments:**
  > **username_1**: In many sports it is common to do practice drills that focus on a particular skill in that sport but don't directly translate to how you would do it in an actual game.  Eg in American football the kicker does practice kicks that warm up the kicking motion but it's still very different from when trying to kick with an opposing team is rushing down on you and the ball positioning / snap is suboptimal. With euro football you might do passing drills etc, but then also do full scrimmages (practice game) because both aspects are useful.  
  > **username_2**: They don't. Some chess puzzles might have unique solutions. Others have several and some might have many solutions.  
  
  ---
  
  ## 7 answers
  
  ### Answer by username_6 on 2022-09-30. Score: 19 | Accepted answer
  
  If someone says to me: "Let's meet at (mumble) on (mumble)", I may respond: "Sorry I didn't catch that."
  
  Tactical puzzles and artistic problems are both (in different ways) about communicating a message, and if the solution is not essentially unique, then the message is unclear.
  
  Uniqueness then becomes a thing in its own right. In a puzzle, it can simplify the automated response, which can just focus on a single line. In a problem, it becomes an aesthetic property: how wonderfully unlikely in a certain position that the correct sequence of moves is unique!
  
  It's perfectly valid (and fun!) to use the property of uniqueness to prune the search space when solving. Solving is a way to learn and appreciate, and difficulty of solving may be a virtue in both puzzle and problem. However this difficulty is subordinate to the nature of the solution. I can legitimately profit (although less) from a puzzle/problem by just reading the solution.
  
  > **Comments:**
  > **username_16**: Straight up to the point, and to the OP: Chess puzzles =!= Chess problems. Although, getting no points for a perfect alternative solution to a chess *puzzle* is also annoying. Which is the reason tactics puzzles better have only one solution, either. Naturally, positional-play oriented puzzles would even be "worse" in this regard.  
  > **username_6**: @username_5 maybe you are joking :) but my little idea here is that there is a significant difference between e.g. "5pm on Sunday" and "9pm on Monday", and if someone is trying to schedule a meeting with me, it's important that I hear their message clearly  
  
  ---
  
  ### Answer by username_3 on 2022-09-29. Score: 11
  
  > Why do chess puzzles need a unique solution?
  
  Because those are the rules. The governing body, the [World Federation of Chess Composition](https://www.wfcc.ch/wfcc-about/hcc/), sets the rules. Their latest [Handbook of Chess Composition](http://www.sci.fi/%7Estniekat/books/hcc8.pdf) includes a Codex where the rules are laid out.
  
  Here are the relevant articles:
  
  > **Article 8 - Author's Solution**
  >
  > Every chess composition must be capable of being solved only by the author's solution. Special features of the author's solution (such as multiple solutions or setplay in helpplay problems) should be expressly stipulated.
  >
  > **Article 9 - Cook**
  >
  > A chess composition is called cooked if it has a solution that differs in its first move from the author's solution.
  >
  > **Article 10 - Dual**
  >
  > A dual is said to occur if, after the first move, there is more than one method of satisfying the stipulation.
  
  > **Comments:**
  > **username_4**: So a puzzle with multiple solutions could be turned into a dual just by introducing a forced first move?  
  > **username_5**: Hmm, don't get me wrong, this is a great answer, but it must be pointed out that the rules you mention only apply to those who wish to follow to them... There is no constraint on web sites, tournaments, nay, on no one at all that don't wish to adhere.  
  > **username_6**: Sigh, this answer might cause folk to mistakenly take you for a jobsworth, username_3 :) "Them's the park regulations! No ball games!" said the park officer blowing his whistle. Unless there was an underlying motivation, it wouldn't be a convention. (And these aren't rules btw.)  
  > **username_7**: It might be helpful to clarify whether a "dual" occurs in a white-to-move puzzle where the black might respond in multiple ways to various moves, but for each move there would only be one follow-up by white that would solve the puzzle, or in those where some responses by black might would allow only one correct line by white, but others would allow the puzzle to be solved multiple ways (e.g. in a mate-in-4 puzzle, a possible black response to the key move would allow immediate checkmate, but white could also waste a tempo and still checkmate black in the stipulated four moves).  
  > **username_7**: All else being equal, a puzzle that requires perfect play on all lines may be more elegant than one that would allow imperfect play on some, but all else isn't always equal.  Adding complexity to a position to make any imperfections fatal in all cases may make a puzzle less elegant than it would be if imperfect play were allowed on some "easy" lines.  
  > **username_8**: @username_7: I would say that there are at least three different possible interpretations of "Black might respond in multiple ways." You could simply require that Black only has one legal move, but that will be rare even in artificially constructed positions, so that's probably not a good restriction to have on a puzzle. You could say that Black must have one move that does not lead to immediate forced mate, but that is still rather restrictive. Or you could say that Black must have one "good" move with all others "obviously wrong," but that is subjective.  
  
  ---
  
  ### Answer by username_5 on 2022-09-30. Score: 10
  
  I'll have to disagree with the premise here. They don't need a unique solution.
  
  For a matter of fact, some Chesstempo tatic puzzles have sub-optimal solutions, but if they still reach a treshhold evaluation (+-1.5 if I recall correctly) you won't fail or pass the puzzle; Instead a blue box will tell you that although that is a winning move, you should keep trying finding the best one.
  
  > **Comments:**
  > **username_0**: Thanks for the chesstempo tip - probably a good tool for training!  Corresponding your side note: there are many such situations. Consider a case where there are two ideas that might work and if candidate move 2 (/idea 2) works, then another (third) move would also work (e.g. Queen on the same diagonal). You can instantly exclude that candidate.  
  > **username_5**: @username_0 Ah, very true, I was only thinking about it from immediately the initial move perspective. I then remove the sidenote.  
  
  ---
  
  ### Answer by username_9 on 2022-09-30. Score: 9
  
  Don't look at chess puzzles as a way of training for competitive chess. Chess problems are a genre of their own. A good chess problem is a piece of art.
  
  By requiring a unique solution we place an extra constraint on the puzzle, making it more valuable. This constraint makes it even more difficult to craft a nice puzzle, and we appreciate that.
  
  See <https://sportstar.thehindu.com/magazine/chess-problem-an-art-form/article29710563.ece>
  
  
  ---
  
  ### Answer by username_10 on 2022-09-30. Score: 6
  
  Basically for the same reason that we're not impressed by a win by
  queen sacrifice if there was also a pedestrian one- or two-move mate.
  
  There *are* chess problems that deliberately have more than one solution,
  often to complement each other in some way. This usually happens in helpmates
  (which are probably of little or no interest to players seeking "training")
  but they're occasionally seen also in direct-mate problems.
  
  
  ---
  
  ### Answer by username_11 on 2022-09-30. Score: 4
  
  I can think of one puzzle that doesn't and can't have a unique solution, but which of the two possible solutions is correct and which is wrong depends on information that can't be derived from the board itself. It's from Smullyan's "Chess Mysteries of Sherlock Holmes" the chapter "Thoughts of a Logician", so I guess it falls under
  
  > Article 8 - Author's Solution
  >
  > Every chess composition must be capable of being solved only by the author's solution. **Special features of the author's solution (such as multiple solutions or setplay in helpplay problems) should be expressly stipulated.**
  
  > **Comments:**
  > **username_12**: Welcome to [chess.se] and thanks for your answer. Could you [edit] your answer to provide more details of the puzzle? I feel that would make it better.  
  > **username_13**: This is a common RPA puzzle (with the interdependence of two white castlings), which Holmes solves using the RS method. The puzzle is not unique. There are a lot of them. It is because of them that the Rules have prioritized PRA over RS. There are no other reasons for the priority of the PRA.  
  
  ---
  
  ### Answer by username_14 on 2022-09-30. Score: 1
  
  Puzzles are usually intended to be hard or at least challenging. Puzzles with multiple solutions tend to be easier since one can arrive at one though multiple avenues. People who design or choose to present puzzles don't want puzzles that are trivial. So the result is that most tend to have one unique solution.
  
  > **Comments:**
  > **username_0**: Actually, it makes puzzles easier. Knowing more relevant features of a problem makes it easier to solve and this is no exception.  
  > **username_15**: Imagine being in the middle of a labyrinth. Would it be more difficult if there were multiple paths leading home?  
  > **username_0**: @username_15 the analogy isn't really fitting. But to answer this using your analogy: Yes! It can be more difficult if you have extra knowledge about the paths when there is only one correct path. E.g. if you have three candidates, but know that two paths merge later, you instantaneously know the right path without any difficulty. The knowledge that there is only one path leading home made it much easier to find in that case, because the others could be excluded so quickly.  
  
  ---
  
  