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What exactly does it mean for a gambit to be unsound? I see this term being used a lot but I have yet to come across a precise definition.

Is it enough for white to lose the advantage that comes with being the first player? What if black is better with best play but not winning?

How is soundness defined if black is the one playing the gambit?

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Adapted from here.

A gambit is said to be 'sound' if it is capable of resulting in an advantage against the opponent. There are three general criteria in which a gambit is often said to be sound:

  1. Time gain: the player accepting the gambit must take time to obtain the sacrificed material and possibly must use more time to reorganize his pieces after the material is taken.
  2. Generation of differential activity: often a player accepting a gambit will decentralize his pieces or pawns and his poorly placed pieces will allow the gambiteer to place his own pieces and pawns on squares that might otherwise have been inaccessible. In addition, bishops and rooks can become more active simply because the loss of pawns often gives rise to open files and diagonals.
  3. Generation of positional weaknesses: finally, accepting a gambit may lead to a compromised pawn structure, holes or other positional weaknesses.

An example of a sound gambit is the Scotch Gambit:

[FEN ""]
1.e4 e5 2.Nf3 Nc6 3.d4 exd4 4.Bc4. 

Here Black can force White to sacrifice a pawn speculatively with 4...Bb4+, but White gets very good compensation for one pawn after 5.c3 dxc3 6.bxc3, or for two pawns after 6.0-0 inviting 6...cxb2 7.Bxb2, due to the development advantage and attacking chances against the black king. As a result, Black is often advised not to try to hold on to the extra pawn.

An example of an unsound gambit is the so-called Halloween Gambit:

[fen ""]
1.e4 e5 2.Nf3 Nc6 3.Nc3 Nf6 4.Nxe5?! Nxe5 5.d4.

Here the investment (a knight for just one pawn) is too large for the moderate advantage of having a strong center.

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    -1 This is copied almost verbatim from wikipedia. – Qudit Jul 30 at 4:57
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    @Qudit to be fair this is a very reasonable explanation about the definition of soundness. What specifically is troubling you with this answer? – NoseKnowsAll Jul 30 at 5:38
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    @NoseKnowsAll It's plagiarism which I find completely unacceptable. – Qudit Jul 30 at 8:16
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    The fact that this answer is copied is not a problem by itself (this is not a school exam after all). The lack of proper citation is, however. – Annatar Jul 30 at 8:25
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    I've added a link to the relevant article to the top of the answer. – vs97 Jul 30 at 8:27
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I would add to vs97's answer that not all sound openings lead to an advantage. Indeed, when playing Black, we are often happy with an equal game, thus defences that lead us there are "sound".

Some openings that don't give anything special for White are still considered "sound" (I don't think anyone would say the London System is unsound). So I would say that for an opening to be unsound, it must have a clear refutation

  • Sure. But that just raises the question of what constitutes a clear refutation. – Qudit Jul 30 at 8:17
  • Well, pretty much nothing in chess, apart from the pieces, is either Black or White. An opening may be "refuted" and still be played by some people becuase they like the resulting position for some reason – David Jul 30 at 8:24
  • That is true. But this question is about a precise definition of soundness and I still am not sure what exactly is meant by the term. – Qudit Jul 30 at 8:26
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    What makes you think there is a precise definition? If there were, who would have the authority to determine what that definition is? An "unsound" opening is just an opening that is not advisable to play because it will create no trouble to a prepared opponent. That's what most people would understand, but there may be subtle differences for each player. This is chess, not logic nor math. It's like asking for a definition of the difference between an imprecision, a bad move and a blunder There is just no "border" – David Jul 30 at 8:29
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    "Some openings that don't give anything special for White are still considered sound". From this you get that White losing the starting advantage is not always enough for an opening to be regarder as "unsound". Black staying better probably is, though – David Jul 30 at 8:32

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