In classical period, ternary or binary forms are the ones used for slow movements. Yet, the second movement of “Appassionata” is in variation form.
Main theme lasts 16 bars and is in small binary form. The A part of the binary can be divided into 2 as 4+4. The last 4 bars are the repetition of the first 4 with a small harmonic alteration. The B part can be divided into 3 subsections as each starts with the same D2 chord. The first bar of each group is in dominant region but the second bars differ from each other.
The first variation is between bars 17-32. Half notes and semiquavers occur due to the syncopated bass, thus the rhythm is accelerated. Yet, the only difference is not the rhythmic changes but also the changes in melody.
The second variation is between bars 33-48. In this variation, the upper part is completely in an accompaniment role with steady semiquavers. The A part of the theme is varied in bass line. The B part becomes counterpointal.
The third variation is between bars 49-80. The semiquavers of previous variation become demisemiquavers. Both in A and B parts of the theme, the melody is first presented in upper line and then in bass line. The melody is syncopated as it’s the case in the first variation.
The last variation is between bars 81-96. The main theme appears again with an interesting change. Nothing is varied, but the melody is partially presented one octave higher. In the bar 96, instead of a tonic chord, diminished 7th chord, namely the 7th degree of f minor appears in order to link this movement to the last one with attacca.