Chord Progressions that Work

    Understanding why certain chords transition well to others is relatively simple when you break it down mathematically.  The key concept to understand is contrast.  When two chords sound similar to each other, they do not create much contrast and probably won’t deliver a quality transition.  Nowhere is this truth more clearly illustrated than in the most commonly used chord grouping there is; I, IV & V.  In almost all instances these chords will provide quality contrast and transitions with each other.  But why is that?  When you analyze the data, it is right in front of your eyes.  The I(i) chord shares only 1 out of 3 tones (2 out 4 with sevenths) with both the IV(iv) and V(v) chords, while the IV(iv) and V(v) chords share no tones (1 with sevenths) with each other.  When we look at the transitions between I and either IV or V, you notice that they always sound good.  The transition between IV and V works as well, but maybe not quite as good.  So if we were going to make a generalization, we could say that the most desirable chord changes involve chords that share 1 tone (2 with sevenths) while those sharing no tones (1 with sevenths) also provide a solid option.  When you transition between chords that share 2 tones (3 with sevenths), the contrast is not as good (especially with inversions).   That’s not to say that using a progression between chords sharing 2 tones never works, but the odds are against you.

    Chords sharing 1 tone (2 with sevenths) – Ideal contrast
    Most common: I & IV,  I & V,  II & V,  II & VI
    Less common: III & VI,  III & VII,  IV & VII

    Chords sharing no tones (1 with sevenths) – Good contrast
    Most common: I & II,  IV & V
    Less common: I & VII,  II & III,  III & IV,  V & VI,  VI & VII

    Chords sharing 2 tones (3 with sevenths) – Less desirable
    I & III,  II & IV,  III & V,  IV & VI,  V & VII,  VI & I,  VII & II