The tonic chord, which represents the key of your song (or song section), acts as a kind of tonal anchor: it sounds like “home”, and when you move away from it, your ears automatically listen for its return. You hear that easily in this basic progression:
C Am Dm G7 C
If you look deeper into how we hear chords, you become aware of something else: more often than not, we’ll automatically assume that the first chord we hear is the tonic chord. This won’t be true if that first chord is something like a G7, because it sounds so strongly like a dominant seventh chord that we just can’t hear it as a tonic. But for basic triads, the first chord we hear is often heard as the tonic until we understand otherwise.
If you like the chords-first songwriting process, there are pitfalls that you need to be sure to avoid. “Writing a Song From a Chord Progression” shows you how to make sure that your chords-first song has great melodies and lyrics.
Since good songwriting is often the art of “manipulating” the musical minds of listeners, it can provide an interesting effect to use a different chord within that progression as your starting point.
For example, take that sample progression but start on the second or the third chord:
Am Dm G7 C
Dm G7 C Am
By starting on a different chord — in these two cases, a minor chord — you give your progression an entirely different mood. But the structure of the progression, and the sequence of chords, stays the same.
So in that sense, you haven’t really changed key at all, you’ve simply changed the starting chord — the chord that gets the most attention.
For Songs Based On One Chord Progression
If you had been working on your song assuming that it was going to use the same progression for both the verse and the chorus, choosing to start your verse on a different chord does something very useful from a musical point of view: it allows you to give the verse a completely different sound and mood.
It’s a great way to create variety and give the impression that you’ve developed a completely different chorus progression, when all you’ve really done is started the verse progression on a chord other than the tonic.
Starting progressions on a chord other than the one you thought was going to be the first chord is also a great troubleshooting technique if you find that you wish you had a more interesting progression. Simply take the progression you’ve come up with, but start further on down the line of chords.
Something else you can do to progressions that just don’t sound inventive or fresh enough: try playing your progression backwards (sometimes doesn’t work, so you’ll need to use your ears). If you like it, try it backwards for the verse and forwards for the chorus.
All this is simply to remind you that you that it’s often worth the time to experiment with your chords. The best result to come from this kind of experimenting is coming up with a different mood, one that might more properly support the melody and the intention of the lyric.