Songwriting Tips: Major/Minor Modulations and Interesting Progressions

I'm always looking for interesting harmonic progressions in my songs, and some of the most satisfying results are subtle modulations that appear simple but are actually more complex than they appear. Growing up as I did on the songs of The Beatles, I do of course take a lot of my inspiration from their examples in this vein, which have been scrutinized in great detail by Alan Pollack.

Take this example from a song I wrote last week. It starts off with a I - ii - V progression, much beloved in all of Jazz and used in songs like Home (as recorded by Bonnie Raitt) and I Shall Be Released (where iii and V substitute for each other).

section 1: A Bm7 E7 A

section 2: Dm7 - C B/G Am7 - , Dm7 - C B/G Am7 - - -, G - , F - - -

which can be written (with the 7ths omitted and 6 implying 3rd in the bass) as:

I ii V I

iv III VII6 i VII VI
( or written as modulation as if it were a modulation to III/C: ii I V6 vi V IV)

What's interesting here is the ambiguity created by the I / III relationship. On the one hand, it could be that the sunny A major of section I gives way to a change to A minor in section II, with the relative major (C major) substituting as the perceived tonic instead of A minor.

Composers since Wagner and Beethoven have been exploiting modulation by a third because it brings with it all kinds of interesting properties. Going from an A major chord directly to an A minor chord (David Gray is a big fan of this, see also the song I'll Be Back) is dramatic but a bit predictable. Going from A major to D minor (minor iv instead of major IV) is interesting because it serves as pivot chord, and following it with a C sounds like ii - I now in the key of C, a third away. Changing from section 2 back to section 1 uses a similar F > A movement by a third where the net effect is the sudden sharping of the C note (FAC > AC#E), a minor>major shift that is also more interesting than a parallel minor/major (same chord) change.

In terms of the structure of the song then what I had so far was

section 1 I ii V I
section 2 iv => aka ii I V6 vi V IV (all /III)
section 1
section 2

I decided the best end of the song (as usual trying to keep under 4 minutes if possible) was to use an extension followed by a slight variation of section 2:

F -
- - - -
C - B/G - Am7 - F G
C - B/G - Am7 - F -
G - F - - - -
G - F - - - -
C

the extension on F is a classic way of making a final push to the end. The harmonic rhythm of the section 2 chords are here elongated to a full measure each (C , B/G, Am7), twice the duration of before. The last variation is the F G C (where before we had Am7 G F), finally making it clear that C and not A minor has become the key we are in.