One grammatical quirk that always annoys me is when people say, "very unique" or "most unique". That shows a basic failure to comprehend the concept. So I am not going to say that I want to look at some of the most unique pieces of music ever written. But I do want to look at the fascinating phenomenon of individuality in music. I think all great pieces of music are very individual, yes, unique in their own way. The most surprising thing about the way they are unique is the simplicity of it. Take this piece for example:
Perhaps the most popular piece from the most-loved classical composer. It is unique, distinctive and individual--instantly recognizable by any music-lover. But it is amazingly simple. The first two measures literally do nothing but outline the tonic harmony--the chord of the home key. It is the musical equivalent of saying "hello". The next two measures literally do nothing but outline the dominant seventh harmony; the musical equivalent of saying "how do you do"? How could such banality be also so popular and, more importantly, so individual?
The mystery of this is related to the problem composers fall into of trying to write distinctive and unique music by writing complicated music. Another related mystery is the difficulty that performers have getting a piece so utterly simple to sound exactly right. This kind of music is very easy to play in a mediocre way, but incredibly difficult to play exactly right!
Notice I haven't answered my own question? Why does this work? Let me put up another example:
Now this is going to be even more perplexing because, guess what, in this very nice piano sonata by Beethoven the first two measures, yep, you guessed it, do nothing but outline the tonic harmony and, yes, the next two measures do nothing but outline the dominant seventh harmony. There is only one extra element: the tiny detail of the turn figure, which he immediately focuses on to end the phrase on a half-cadence. So Beethoven in this excellent and individual piece, his first-published piano sonata, does almost the same thing that Mozart did in his excellent and individual piece, except he adds a turn. They actually pay people to do this? Not only that, but Mozart and Beethoven are considered to be two of the greatest creative geniuses in music.
You should go back and listen to both examples again, perhaps a few times. Both composers recognize the power of the language of harmony at the time and found ways to use that power--in its simplicity--and still make music that was individual. Of course, the "two measures of tonic, two measures of dominant" model wasn't the only one that had been developed. You could have "four measures of tonic, two measures of dominant" if the harmonic energy needed to be channeled in a different way. There were other kinds of progressions such as the one Beethoven used in the Moonlight Sonata:
For this piece, Beethoven takes a very old harmonic progression that goes back a couple of hundred years and makes one small change. What I am trying to reveal here is that great music is often very simple, based on a limited number of simple harmonic ideas. All it takes is a suitable rhythmic texture and perhaps one tiny variation in the basic plan and there you have it. Uh-huh...
That brings us to the real mystery: if these great pieces of music are so simple, why are there so few of them? Well, there are more than you would think. One of Mozart's serenades has become very popular, but he wrote dozens of them and most are very, very good. Beethoven wrote thirty-two piano sonatas and none of them are anything less than spectacular and some much more than that. This is why people like Daniel Barenboim give series of concerts in which they play all thirty-two sonatas.
But we have to realize that the brilliant simplicity of these pieces is not so obvious before they are written. Thousands of pieces start with two measures of tonic followed by two measures of dominant and are dreary bores because all they do is follow some pre-determined model. What makes Mozart and Beethoven great is that they can build something remarkable upon a simple foundation. And keep doing it in piece after piece.
Both of these masters are from the Classical period and it was typical of that music that melodies be built by outlining the basic harmonies. Hundreds of composers did it, mostly to rather mediocre effect. But Mozart and Beethoven (and Haydn, who designed a lot of the basic language) did it surpassingly well. The delight of listening your way through all the Beethoven piano sonatas with the score, is seeing how he finds a new way of working with the basic materials in every sonata. Creativity: discipline plus invention.