# Understanding dissonance in Mozart's String Quartet No. 19

I perfectly understand how the dissonance is built as explained by Wikipedia :

The first movement opens with ominous quiet Cs in the cello, joined successively by the viola (on A♭ moving to a G), the second violin (on E♭), and the first violin (on A), thus creating the "dissonance" itself

However, I fail to understand what immediately follows :

and narrowly avoiding a greater one.

What is that "greater dissonance" that is "narrowly" avoided. ?

A/Ab if the viola had not moved to G ?

• Yes, I think it means that the dissonance is the tritone between Eb and A, but that if the viola hadn’t changed, Ab against A would be a greater one. Commented Jan 29, 2022 at 19:03
• (Also, even on a G, the viola sets up a M2, which counts, but is lesser than a m2.) Commented Jan 29, 2022 at 19:05
• i agree with this comment of Andy. This would have been exactly my answer. Commented Jan 29, 2022 at 22:40
• May be this link will help: (p. 733, ☆466) archive.org/details/theoryofmusicalc02webeuoft Commented Jan 29, 2022 at 22:57
• Thanks a lot @AlbrechtHügli for this present I knew nothing about. I must admit having had a hard time on this paragraph since I discovered that things are much much more complicated that what I had primarily imagined. And even if it does not precisely answer my question, what I learnt was actually worth the time I spent. If you are interested in earning SE "reputation" Feel free to build an answer from your comment, I'll be happy to put a bounty on it. Commented Jan 30, 2022 at 1:43

Yes, the "greater dissonance" that the sentence refers to is probably the fact that the viola moves away from Ab at the very moment that the first violin enters on A natural, and a minor second (ignoring octave displacement) would be an extremely striking dissonance.

As it is, the intervallic dissonances in just those first two measures are the major second of the viola's G against the first violin's A, as well as the tritone of that A against the second violin's Eb (and, on the last beat of the second measure, a D in the second violin against a C in the cello).

Ultimately, though, the disquieting effect of this opening has to do with more than "X against Y" intervallic clashes. I'm sure it's been analyzed elsewhere in more depth, but at a quick glance, perhaps the most striking issue is the amorphous ambiguity about establishing the tonal center.

The overall movement is in C major, and sure enough, the cello starts cranking out Cs. We might expect an E natural to stack on top next, to cement the major triad, but instead we get an Ab. That might suggest that the cello's C was in fact the third of an Ab chord, and the second violin's entrance on Eb supports that. But then the first violin pulls the rug out from under us with its inexplicable A natural, and beats later, by the last beat of the second measure, we have C-D-F#-A —turns out the C was the 7th in a D7 all along? And then it resolves to a G (albeit over a B in the bass)—okay, I see where this is going; G is the dominant and we're headed for the C major we were promised all along, right? But then the cello simply sidles down chromatically to Bb, while the first violin rises in a shriek to Db... and we know it's going to be a long, strange trip back to C.

• Thank you for that detailed answer I will reward as promised. One point that looks surprising to me is when you write "cello's C was in fact the third of an Ab chord". While of course agreeing this is a possibility, wouldn't it be more immediate to assume from the cello's start an ambiguity (C maj / C min) then C min determined by viola's Ab, C min definitely cemented by violin's Eb ? Commented Feb 3, 2022 at 9:51
• @MC68020 1) Thanks, though I'm not particularly concerned about accumulating reputation (or at least, I was in an all-fired hurry to pass 3,000 and be able to vote to close/reopen!, but now it's less urgent). 2) I'm talking not so much about key as about chord. Given a triad, of course we know what chord we're hearing. Given only two pitches, context and habit prompt us to guess the third pitch. So when an Ab is added to the C, we might assume the missing pitch is Eb, and maybe (within the key of C) we have a bVI which might go to V. Commented Feb 3, 2022 at 14:14

A/Ab would definitely be an unpleasant dissonance uncharacteristic of Mozart.

Mozart was a Romantic style composer who lived not long after the end of the Baroque period. Romantic music was expressive and emotional. Dissonances in this kind of music are common to express doubt, loss, or sadness.

But, the Romantic composers did not use dissonances like A/Ab. While clashing notes can show the listener emotion, extreme dissonance like the one avoided here is used in modern music, not Romantic. If Mozart was a modern composer, he would have leaned into atonality in his pieces, which we can rule out, because he didn't do this (courtesy of the 600, give or take, masterpieces he wrote during his lifetime).

So yes, your friendly Wikipedia editor is referring to the A/Ab dissonance because he/she probably knew Mozart in and out, and wanted the reader to know how Mozart viewed great dissonances, as opposed to lesser ones.

• Mozart was in no way a Romantic composer. He was the definition of Classical. And baroque, classical, and romantic all used dissonances like A/Ab at various times and in various ways. Commented Feb 3, 2022 at 4:57
• While Mozart's music sounds more heated and harmonically adventurous than the average Classical-era style galant (at least from my findings), it still doesn't push him away from being consistently categorized as Classical-era (unlike Beethoven, whose even more heated and harmonically adventurous music actually has music historians splitting more halfway between Classical and early Romantic). Regardless, A against Ab is not unheard of in Romantic-era music, anyway (especially in V(b)9 chords). Commented Feb 3, 2022 at 13:16