I'm reading about dominant seventh chords and this is a summary of the notation that my book has introduced:
After a few moments' thought, I can deduce the convention for denoting the different positions in which a dominant 7th chord may appear -- the intervals from the bottom note of the chord are listed to the right of the V.
I'm a bit baffled, however, by the way they are abbreviated. Why do we choose to omit the 3 when abbreviating the first inversion, but omit the 6 for the second inversion?
My only guess is that the notes which form a 2nd are the only ones listed, as that is enough to reconstruct the correct inversion of the original chord (the 3rd inversion being an exception to this as the bottom note itself is one of those two notes).
Is this what is going on, or is there some other reason? Or is it simply arbitrarily decided upon and I ought to memorize and/or get used to it?