I'm studying Andantino no. 15: in 'Studi per Chitarra' by Ferdinando Carulli but I can't figure out what the chords are under the ones, the two and the four. I think 1 could be ii diminished but I was taught ii diminished -> i was a bad chord progression. As for two and four I have no idea.
1 Answer
The chord at the 1 is an ordinary ii°6 chord. It resolves into a i6/4-v chord progression the first time and a i6/4-V chord progression the second time. It's possible that the v chord is passing and itself a temporary fake-out, as i6/4 normally resolves with very high probability to a dominant-function chord such as V...
...and the chord at the 2, which the v chord resolves to, is a vii°4/3 chord. This is a dominant-function chord, and it resolves to a i6 chord.
The measure at 4 involves a long elaboration on the dominant function. The A is an accented non-chord tone (specifically, an appoggiatura), while the rest of the notes can be explained as I6/4-V7 in C major.