Is this phrase ending a half cadence, imperfect authentic cadence, or neither?

Question

I'm working on this for a music theory class. By my analysis:

1. Song is in key of A major
2. The chord for measure three uses the 4th scale degree, or IV
3. The chord for measure four is the tonic, or I

I'd say that this phrase ends on a plagal cadence (IV to I) but the instructions insist that this is a HC or IAC. Am I nuts?

Answer 1

There are a lot of problems with the homework question.

But first, here's what they're intending:

1. Look only at the final note (sol) and chord (I).
2. Is it an HC? No, because the chord would be E.
3. Is it an IAC? Yes, because it's a I chord, but do is not in the soprano.

As far as the book is concerned, the correct answer is IAC.

Why the question is problematic:

1. The progression is IV-I, so if it's a cadence at all, it's a plagal cadence, as stated in the question.
2. It's not a cadence. It's just two chords that happen to be the same ones as in a plagal cadence, but there's no sense of "ending" at this point. (Okay, granted, this is more a matter of interpretation/opinion. A reasonable case could be made that it's a cadence.)
3. It's not a phrase. It's the first half of a phrase. Had they included the next four bars and asked the question, then the answer would be HC.