Even if I am able to demonstrate some aspects of a particular piece by Mozart, it will not necessarily give you any tools to appreciate the next piece by Mozart. The task of a good music theorist is to somehow "explain" how music works, but at the end of the day, all he can do is give a generic account. He can explain everything except that touch of unique genius that makes a piece a great one instead of just a fairly good one. This is one of those awkward things about music and art in general that make it seem so mysterious to the uninitiated. I am going to take a look at a couple of pieces by Mozart and then I think you will see what I am talking about.
Now the question is, should I pick a pair of pieces that are superficially similar so we can see how different they are underneath, or just pick two different pieces? Agh! It will probably be more interesting to pick two pieces that are, on the surface at least, fairly similar, as I think that will make the contrasts more pointed.
I'm going to pick an early work, not terribly well known, and a later, very famous movement. Both of these are andante. The first piece is the middle movement from one of Mozart's divertimenti for strings he wrote after returning to Salzburg after his second trip to Italy in 1771. He was sixteen years old and, being Mozart, a fully mature composer. This is just the middle of the three movements and we are just going to look at the first theme:
Here is the first section in score:
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The piece I am going to compare to this is the andante, the middle slow movement, of the Piano Concerto in C major, K. 467. This was one of a string of extraordinary concertos Mozart wrote in Vienna, this one in 1785 when he was twenty-nine years old. The first theme takes exactly the same time to play as the section of the divertimento we just looked at: 1:23:
Here is the score of the first theme. I am just quoting the string section (the winds come in in measure eight and add harmonic color) as the first violins have the theme. At the end of this section, the piano enters with its statement of the theme.
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This theme has one measure of accompaniment before the melody begins. It comprises one long, long single theme (even with discernable sections) that goes on for twenty-two measures, but seems almost timeless. The most striking thing about this theme is the enormous leap in measure eight and again in measure ten down two octaves and a third!! This is followed by a sequence of the most delicate and haunting dissonances over a dominant pedal starting in measure twelve. Then there is a deceptive cadence to D minor in measure nineteen, lent extra weight by tonicizing the vi chord (D minor) with its viiº7. It sounds as if this might be a modulation, but it is immediately followed by the real cadence ending this very long phrase on the tonic, F major. Is it just an artifact of the way the scores are laid out, or does this phrase sound much longer than the first section of the divertimento we looked at?
So, two movements, both andantes, and the opening themes each take 1:23 to play. But how remarkably different they are! Sure, they share the same harmonic language, use similar note values and so on. But where it counts, in the ear of the listener, they are so very different.
There are so many things I haven't talked about, such as, for example, the way that the first two measures of the piano concerto theme, with the double-dotted rhythm, is answered and balanced, not by elaborating it, but by simplifying it! The answer to those opening measures uses only halves, quarters and eighths. Most pieces by most composers would put the simpler idea first, but Mozart does the reverse and makes it seem magical.
Every time a composer of Mozart's stature approaches a piece he solves the eternal problems of unity, variety, complexity, simplicity and so on in different ways. This is why, if you want to talk about the music with any degree of specificity, you have to look at each piece as an individual work of art. The problem for theorists, is that they try to abstract the things composers do into general rules or stylistic traits. This only goes so far and usually results in squeezing what is most obvious to the listener, out: the magic.
Just for fun, let's end with yet another Mozart andante (he wrote hundreds), this one from the Sinfonia Concertante for violin, viola and orchestra. Notice how the theme is very, very different from both of the ones we just looked at: