One of the most interesting and useful concepts in harmony is the secondary dominant. Once you understand how they work, you'll see how they can transform your music, adding tension, colour, and a sense of movement.
What Are Secondary Dominants?
A secondary dominant is a chord that temporarily functions as the dominant (V) of a chord other than the tonic (I). In C major, the dominant chord G7 resolves to C. But if we want to temporarily emphasise D minor (ii), we use A7 — the dominant of D minor. A7 is a secondary dominant (written V7/ii).
In Action
Normal progression: C – Dm – G – C
With secondary dominant: C – A7 – Dm – G – C
The A7 leads naturally into Dm, creating a temporary sense of tension before moving forward.
Common Secondary Dominants in C Major
- V7/ii: A7 → Dm
- V7/iii: E7 → Em
- V7/IV: C7 → F
- V7/V: D7 → G
- V7/vi: B7 → Am
How They Affect Harmony
Secondary dominants create tension and release, temporary tonicisation (making a chord feel like a brief tonic), smooth voice leading, and expanded harmonic possibilities. They allow you to add colour and variety to otherwise predictable progressions without changing the overall tonality.
So the next time you're writing a progression or improvising, try adding a secondary dominant. You'll be amazed at how such a small harmonic shift can make a huge difference.