[ 1. Is it just jargon to elevate one's
favourite composer over another? What say you?
2. Or else in a more objective, technical sense, perfect form means a composer
follows the form perfectly without deviation, which doesn't prove one's a genius. ]
I'm reminded of quotes by Ravel and Sibelius. The one by Ravel seems to imply case 1, whereas the one by Sibelius seems to imply case 2.
"He (Ravel) told the pianist Marguerite Long, who premiered it (Concerto in G Major), that he composed the exquisite slow movement "'two measures at a time,' with the assistance of Mozart's Clarinet Quintet."
Mozart was his favorite composer-Mozart "remains the most perfect of all," he remarked, repeating this evaluation in one way or another over the years."
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Paris on the Brink: The 1930s Paris of Jean Renoir, Salvador Dalí, Simone de Beauvoir, André Gide, Sylvia Beach, Léon Blum, and Their Friends, by Mary McAuliffe, Page 144 >
"Sibelius himself remarked that: 'To my mind a Mozart Allegro is the most perfect model for a symphonic movement. Think of its wonderful unity and homogeneity! It is like an uninterrupted flowing, where
nothing stands out and nothing encroaches upon the rest.' This description also suits the first movement of his own Third Symphony very well."
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Sibelius, By Andrew Barnett, Page 183 >
"perfect" is one of those terms that are overused these days, so it is too vague to be meaningful in serious discussions. I think whoever uses the term should be specific what precisely he means by it. I think, in the common usage of the term in the case of Mozart, the term can mean both positive and negative connotations: "Mozart has craftsmanship, but nothing in his music really stands out". I don't think Sibelius used the expression "nothing stands out", to describe Mozart negatively. But sometimes, depending on the context and how it's used by people in other cases, the phrase can be perceived as having a negative connotation.
There's actually a lot of ingenuity and interesting elements in Mozart's form, take K. 491, for example:
https://en.wikipedia.org/wiki/Piano_Concerto_No._24_(Mozart)
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The orchestral exposition, 99 measures long, presents two groups of thematic material, one primary and one secondary, both in the tonic of C minor. The orchestra opens the principal theme in unison, but not powerfully: the dynamic marking is piano. The theme is tonally ambiguous, not asserting the home key of C minor until its final cadence in the thirteenth measure. It is also highly chromatic: in its 13 measures, it utilises all 12 notes of the chromatic scale.
The solo exposition follows its orchestral counterpart, and it is here that convention is discarded from the outset: the piano does not enter with the principal theme. Instead, it has an 18-measure solo passage. It is only after this passage that the principal theme appears, carried by the orchestra. The piano then picks up the theme from its seventh measure. Another departure from convention is that the solo exposition does not re-state the secondary theme from the orchestral exposition. Instead, a succession of new secondary thematic material appears. Musicologist Donald Tovey considered this introduction of new material to be "utterly subversive of the doctrine that the function of the opening tutti [the orchestral exposition] was to predict what the solo had to say."
One hundred measures into the solo exposition, which is now in the relative major of E♭, the piano plays a cadential trill, leading the orchestra from the dominant seventh to the tonic. This suggests to the listener that the solo exposition has reached an end, but Mozart instead gives the woodwinds a new theme. The exposition continues for another 60 or so measures, before another cadential trill brings about the real conclusion, prompting a ritornello that connects the exposition with the development. The pianist and musicologist Charles Rosen argues that Mozart thus created a "double exposition". Rosen also suggests that this explains why Mozart made substantial elongations to the orchestral exposition during the composition process; he needed a longer orchestral exposition to balance its "double" solo counterpart."
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The third movement features a theme in C minor followed by eight variations upon it. Hutchings considered it "both Mozart's finest essay in variation form and also his best concerto finale."
"Variations II to VI are what Girdlestone and Hutchings independently describe as "double" variations. Within each variation, each of the eight-measure phrases from the theme is further varied upon its repeat (AXAYBXBY). Variations IV and VI are in major keys. Tovey refers to the former (in A♭) as "cheerful" and the latter (in C) as "graceful". Between the two major-key variations, Variation V returns to C minor; Girdlestone describes this variation as "one of the most moving"."