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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"?

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    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.
    – eps
    Commented Oct 1, 2022 at 15:32
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    They don't. Some chess puzzles might have unique solutions. Others have several and some might have many solutions.
    – Robbie Goodwin
    Commented Oct 1, 2022 at 21:25

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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.

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    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.
    – Hauke Reddmann
    Commented Sep 30, 2022 at 7:44
  • @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
    – Laska
    Commented Oct 3, 2022 at 14:44
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Why do chess puzzles need a unique solution?

Because those are the rules. The governing body, the World Federation of Chess Composition, sets the rules. Their latest Handbook of Chess Composition 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.

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    So a puzzle with multiple solutions could be turned into a dual just by introducing a forced first move?
    – qwr
    Commented Sep 29, 2022 at 23:13
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    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.
    – LoremIpsum
    Commented Sep 30, 2022 at 1:31
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    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.)
    – Laska
    Commented Sep 30, 2022 at 2:09
  • 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).
    – supercat
    Commented Sep 30, 2022 at 17:12
  • 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.
    – supercat
    Commented Sep 30, 2022 at 17:17
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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.

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    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.
    – Hauptideal
    Commented Sep 30, 2022 at 9:02
  • @Hauptideal Ah, very true, I was only thinking about it from immediately the initial move perspective. I then remove the sidenote.
    – LoremIpsum
    Commented Oct 1, 2022 at 0:18
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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

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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.

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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.

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    Welcome to Chess and thanks for your answer. Could you edit your answer to provide more details of the puzzle? I feel that would make it better.
    – Glorfindel ♦
    Commented Sep 30, 2022 at 14:44
  • 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.
    – Элси Ринген
    Commented Jul 20 at 20:25
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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.

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  • Actually, it makes puzzles easier. Knowing more relevant features of a problem makes it easier to solve and this is no exception.
    – Hauptideal
    Commented Sep 30, 2022 at 14:00
  • Imagine being in the middle of a labyrinth. Would it be more difficult if there were multiple paths leading home?
    – Hunaphu
    Commented Oct 2, 2022 at 19:17
  • @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.
    – Hauptideal
    Commented Oct 4, 2022 at 23:32

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