Alban Berg's Impromptu in E major for piano is a student piece, one whose primary purpose seems to have been the exercise of two things: 1) extended manipulation and development of a single thematic idea, and 2) constant hemiola. The Impromptu, which dates from around 1908, is written in 6/8 meter, but there is as strong a sense of 3/4 to the bars as 6/8. This hemiola, or cross-rhythm, combined with the swaying dotted rhythm at the head of the theme, gives the music a distinct waltz-like flavor.
Sixteen bars are allotted for a thorough getting-to-know-you of the theme. Then we are off to C major -- suddenly, but not particularly startlingly -- for some development and, ultimately, a reprise of the opening music (the fact that this internal reprise is made in the wrong key seems a matter of pride to the music -- it is blasted out, fortissimo!). Berg liked some of this central section music so much that he surrounded a big portion of it with repeat signs. A whirlwind eight-bar transition (marked Rasch by the composer, it is like the transitions of many nineteenth century waltzes, which suddenly speed up on their way to the next section) brings us back to E major for a very brief recapitulation of the theme in its original tonal guise.
There is nothing shocking about the music of the E major Impromptu -- it is after all, a student piece, and Berg's teacher was quite intent on building a solid, tradition-oriented set of skills. But a wonderful bit of chromaticism is heard each time the melody reaches its last cadence -- the music seems to just slip down into the E major resolution, almost as though by accident.