Waehnen, I doubt anyone is going to convince you otherwise as that's how YOU, personally, hear this wonderful piece. I don't! Is this a serious work? Well of course it is but to dismiss his use of humour throughout the quartet, for me, is way off the mark. Good humor involves having a sense of irony, and appreciation of ambiguities. Do you really believe Beethoven had no sense of humour as he approached the end of his life? Many of his students and friends have provided a high volume of anecdotal evidence of his very particular sense of humour right until the very end (Ries, Czerny, Holz, Shuppanzigh, etc). Remember this is a guy who used to hide behind doors and jump out with a "Boo"! Had he really lost all his humour when he got to the end? Well not according to Holz and Czerny in particular. Listen to that ending and how, after a few slow and questioning repeats of Es muss sein, all four strings start playing pizzicato, as though they are tiptoeing out of the room before coming back for the bold ending. Can you not see any humour there? If the movement is about how to resolve your own immortality, then what is to say that Beethoven is facing his own death by overturning fear or arguably turning it into joy but for me it's not about that. We don't know for sure what it really is all about because Beethoven never said but I still think Beethoven would be enjoying leaving us guessing. As I said previously, personally, I still see a lot of paradoxical humour in that scherzo and joyful playfulness in the final movement . Here's just a few professionals / string quartet ensembles who agree....
"The second movement is a quicksilver scherzo. The parts at the beginning stage a rhythmic comic act, ill-fitting and awkward, everyone sitting on the wrong beat, then suddenly falling heavily onto a unison E-flat that is also off the beat, stuck in the wrong meter for awhile before righting itself (sort of).... (Brentano Quartet)
Later they go on to say of the finale..
"Then follows the main Allegro section, joyful and affirmative, marked “Es muss sein!” — it must be! Two-thirds of this movement then unroll with barely a cloud on the horizon. All is happiness, high jinks, carefree melody, playfulness.. " (Brentano Quartet)
"The scherzo is rife with rhythmic jokes likely to convince players that they are counting wrong, or that the composer is off his rocker. The four parts tug at each other in four different rhythms or get together to run up and down and stop for no good reason.. "
(John Mangum - Artistic Director LA Philharmonic)
" Whatever the case, it’s a brilliant finale. The opening is full of tension (somewhat humorous, given the context?) as the “Muss es sein?” motive is enigmatically shared between the instruments. The ensuing Allegro is playful, joyful and features a simple but endlessly useful theme for Beethoven to spin out his musical ideas. We toggle between the home F major up to A major and down to D major.... " (New Orford Quartet)
".... It is as though Beethoven is laughing at himself and at his audience for taking this little motif so seriously, and making such a mystery out of his whimsical Muss es sein? which was no enigma at all!" (de Marliave 'The Beethoven Quartets' 1928)
"the comedy, which is so apparent in the Allegro, already starts in the “Muss es sein?” introduction, imagining characters from commedia dell’arte.. ." (Kerman 'Beethoven's Quartets 1966)
"... Here as for the greatest literary artists, above all his beloved Shakespeare, comedy is not a lesser form than tragedy but is its true counterpart, the celebration of the human in all things.”
(Beethoven scholar, Lewis, Lockwood - 'Beethoven - The Music and the Life' 2003)
"The Allegro has by some commentators being characterised as either “ironic” or “forced”, but in my eyes the completely honestly good-natured second theme certainly excludes the former idea, even if the recurring “Es muss sein!” statements have a certain touch of jauntiness. If it is forced, it is in the most humorous way. And the little coda marks the ending (and indeed the whole piece), twinkly-eyed and humorous as it might be, with honesty and kindness.... "
(Martin Saving, Elias String Quartet - 'The Beethoven Project)
" No one listening to this profoundly spiritual music could suspect that it was based on so mundane a matter as money; but as an example of Beethoven's down-to-earth sense of humour, the paradox is altogether typical"
(Misha Donat - writer, lecturer and former BBC Radio 3 producer)
"The finale reacts with an indescribable blend of fun, humour and seriousness, quoting the joke phrase Beethoven wrote..."
(Robert Simpson - composer)
"The humorous side of Beethoven's personality seeps into his music such as in his Quartet in F, Op. 135, where more hijinks ensue in the Vivace and the music becomes completely berserk..."
(Nicholas Kitchen - Borromeo Quartet)
Tbh, I could keep going and give you quotes from a host of string quartets who have discussed this piece but I can't be bothered (this post has taken too long as it is) but I would suggest that your interpretation seems at odds with all the above (nothing wrong with that - it's your personal reaction to the music) as these ensembles (below) reference the humour in this quartet in either their sleeve notes or program notes... ..
Takacs
Ebene
Miro
St Lawrence
Ehnes
Pacifica
Daedalus
Guarneri
Tokyo
Escher
Danish
........
I ran out of patience looking after that, tbh (and Mrs Merl was moaning at me to finish a job) , but I suspect I could find at least another 20 if I looked tonight. I know what you're driving at, Waehnen, but I still don't hear it how you do. I doubt we hear the other quartets the same too. A personal reaction is just that.