Piano Sonata no. 15 in D major Op. 28 third movement
The A section ambiguously starts out in d major. It is ambiguous because of the f sharp's starting the piece. The A section consists of 4, 8 bar phrases. However, none of these phrases are linked together as a period; the A section is just a phrase group. In bar 8 a PAC occurs in D major. In bar 16 a PAC occurs in A major, signifying a modulation. Bar 17 returns in D major. Bar 24 has a PAC occuring in D major. Then in bar 32 another PAC occurs in A major. Some notable structural phenomena take place in bars 17-20 with a new dynamic. Same with 25-28. Because the A section ends in A major the A section is continuous. More phenomena takes place at the B section, as the dynamics are softer and the note values are longer in the melodic gestures. I would consider the B section up to bar 49 as a section, as there are not notable strong cadences. Bar 49 brings back the A section material in its original key of D major. A PAC occurs in bar 56. Bar 57 begins a development period of the A section material as the melodic gestures in the right hand are developed. This ends in bar 68 with a PAC. This is rounded binary form. The trio is a coda in this form. It starts off in D major and finally modulates to b minor.