I got into a conversation with someone about something in my first harmony theory book. Horwood stated that phrases often began (used to begin?) with I6 vii6 I or I vii6 I6 (I guess that translates into C/E B/D C or C B/D C/E). The other person thought that the vii6 was actually a V7 which it can be if the G is left out. The main question is whether the version I learned is common or it's just in the old book that I have.

It's a common opening in classical music. These chords support a melody going 1,2,3 or 3,2,1. It's not a requirement; probably more pieces start with something eles, but I haven't counted.

Whether vii06 is just a V7 with the root missing or a separate chord is more a matter of labeling choice than anything else. Should the vii06 proceed to a I, it has a dominant function as would V7. Of course (in a sequence or a complete cycle of fifths, usually) vii06 may proceed to a iii chord where it doesn't really behave like a V7.

Neither Horwood nor the other person is wrong.

My main thought was that since it's I vii6 I6, then it is not moving to the tonic because it's already there, so it's not like a dominant function. The tritone in the vii6 simply reinforces the tonality since it pulls back to the tonic. Maybe it doesn't matter that much what it's called if we know how to use it.


That makes sense. when I did the exercise a year ago I was following the instructions relatively blindly. I thought about it again because I learned some things about the tritone and it seemed to click. But then the question came up about the V7. Thanks.

A dominant is no less a dominant for being between two tonics.

It was a common convention to use such a progression because it opens the possibility of a neat effect called "voice exchange" in compositions. In 3 to 4 part writing especially, one of the voices will be assigned a descending line of 3-2-1 while another an octave (or more) above or below will play/sing 1-2-3. It could be noted that instead of vii6, V6/4 was often used for a more "stable" sonority. In such cases this would be known as a "passing" 6/4.

I V6/4 I6

I6 V6/4 I