Chopin - Prelude in F-Sharp Major Op. 28 No. 13

Once again we are in the simple ternary section of the book, and this is the form of this prelude.

The first phrase consists of the first six measures. This phrase modulates from F-sharp major to C-sharp major ending on a PAC though the PAC is short lived. You could make arguments for some PAC's in F-sharp throughout the first few measures, but the initial chord is immediately followed by the seventh in the bass which takes away the strength of the PAC. The next measure and a half just has the bass line doing a transitory line back into F-sharp major. The second phrase begins parallel to the first; measures 9-12 are almost identical to measure 1-4. However, the downbeat of measure 13 has the seventh in the tonic chord and from here the piece wanders around and no cadence is reached until measure 18, where a PAC in F sharp is achieved. The next two measures make sure the listener knows that the key is F sharp minor and serves as a terminative function for the A section. This makes this section closed.

The B section has major differences compared to the A section. The eighth notes in the left hand become double stops, an eighth note line is added to the right hand, a key change and markings of "piu lento" and "sostenuto" on the music. I don't have a 100% feeling of key for this section, but since most of the bass line is hanging around the key of D sharp minor, it is probably the key. Once again, there are feelings of tonic but not strong enough to be a cadence. This section is nine bars long and modulates back to the original key of F sharp major.

The return of the A section is only ten bars long. The first couple of bars are parallel with the opening A section, but then there is additional development of the main theme and a PAC in F sharp major in the sixth bar, eighth bar, and the last two bars serve a terminative function to end in the key of F sharp major.