There’s this idea out there that Mozart’s music is the hardest to play on the piano.
It sounds obscene on the face of it: Who, stepping onto a professional concert stage, can’t play a simple alberti bass? Mozart’s music is just melody and accompaniment. Any child can play it! The technical challenges are nothing compared to the romantic virtuosity of Liszt or Rachmaninoff’s thick, fast moving chords or busy textures.
This is not wrong on a superficial level. There aren’t nearly as many notes in a 15-minute Mozart Sonata versus a 15-minute Liszt tome. You cover a lot less of the keyboard in classical repertoire, as opposed to later works.
But the idea does start to fall apart: Mozart’s music was written on a less-evolved piano which had a much lighter action, and some of his busy, scalar passagework could be played more brilliantly with less physical demands on the pianist. Secondly, Mozart’s music fits some pianist’s hands better. The bigger your hand, the more precise and delicate your fingers must be.
It is easy to look at Mozart’s music as rather simple, but in reality, he rarely writes a simple Alberti bass. You hear it in the most stereotypical examples, like the beginning of his Sonata in C K 545, but for the most part, his accompanimental patterns are much more inventive and varied.
The idea that Mozart’s music is so difficult comes from the fact that it is so musically delicate. It’s in fact because of these lean textures, where there’s nowhere to hide, that his music is a feat to play. In later music, wrong notes can be hidden by the damper pedal (they shouldn’t, but everyone slips up!), but you simply can’t get away with using the pedal just anywhere in Mozart. His passage work requires rhythmic precision. It’s easy to hear the difference between beautiful rubato, playing with time for expressive purposes, and simply not being able to keep time, when you try to be expressive in Mozart’s music.
It’s deceptively easy to just play Mozart’s music right off the page. The melodies and harmonies are beautiful in and of themselves. But there’s so much to Mozart underneath the surface of the score, and the beauty of Mozart is to play his piano music as if it’s an opera scene. You need to have beautiful, charismatic characters who interact with each other. You need to hear the drama of the plot.
So all of the slurs in Mozart become very important. The interaction between the right hand and the left hand. The passagework aren’t just series of notes, but they have to alternately invoke excitement, frenzy, exuberance, and frowns.
Evidently Artur Schnabel, one of the oldest pianists who was recorded playing Mozart, and indeed, who spent his life dedicated to classical composers like Mozart and Beethoven, said, “Mozart is too easy for children, but too difficult for professionals.” No less a master of the classical style than Alfred Brendel elaborated on that mentality this way:
In Mozart's keyboard works everything is exposed. There are relatively few notes and each of them counts. Not only that you find the right key, but that you give each key the right nuance, the right inflection. If you are not careful you fall into a trap. This is also why these pieces are relatively rarely performed. I think that most players shy away from them. They either don't see the complications and think the pieces are too easy, or they do see the complications and find them too difficult. I decided that I should tackle these sonatas because it will be too late if I don't do it soon.
"Modern performers seem to regard their performances as texts rather than acts, and to prepare for them with the same goal as present-day textual editors: to clear away accretions. Not that this is not a laudable and necessary step; but what is an ultimate step for an editor should be only a first step for a performer, as the very temporal relationship between the functions of editing and performing already suggests." -Richard Taruskin, Text and Act