Ok, so first off--I think it's pretty obvious that Clara wrote this one, mostly because it doesn't start out in parallel octaves. (or maybe she just had quite a lot of input)
So the ambiguity sometimes throws me for a loop...but here goes:
We start in Bb major and have an IAC in measure 4. We then modulate to the dominant F major and have a PAC in measure 8. Measures 9-12 bring us to an IAC in the key of F's dominant C major. At measure 16 we find ourselves in C Major's minor dominant g minor for a PAC. These first 16 measures are an example of a modulating parallel symmetrical double period. (does all that stuff work together?) The cadences of the first 16 bars are as follows: IAC, PAC, IAC, PAC. All of these cadences are in the dominant of the predecessing key. How great is that? good thinking, clara...i mean...bob. Oh yeah, measures 17 and 18 are a cadential extension ending on an IAC...which seems sort of week (bob had input again...obviously)
At measure 19 we go to the key of G major (which is Bb's chromatic mediant!). This next section strikes me as sort of ambiguous cadentially. If notice is made of the notated phrasing--there are 1 bar phrases. however, this seems like sort of a cop-out. If we say there are 3 2-bar phrases then it's just a phrase group. that seems like it could work. the first one ends in measure 20 with an IAC, the second with a HC in m. 22 and the third an IAC in the key of Eb.
The Eb takes us to the repeat of the A section and back to the key of Bb Major. The melody is exactly the same, but an octave higher. The structure is exactly the same as the first exposition of the A section. Phrase 1: Bb: m. 28 IAC Phrase 2: F: m. 32 PAC Phrase 3: C: m. 36 IAC Phrase 4: g: m. 40 PAC Cadential Extension: m. 41, 42. Ends on an IAC. Why the ending on a weak cadence??? ugh.
So anyway, I certainly hope we talk about this one in class...cause I'm not sure if I'm right--at all.