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AP® Music Theory · Unit 7 · Topic 7.1

Spelling Secondary Dominant Chords

A secondary dominant is a major or dominant seventh chord built on the fifth degree of a chord other than the tonic, borrowed to pull strongly toward that chord as if it were briefly home.

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Every chord in a key, not just the tonic, can act like a temporary home. To spell a secondary dominant, pick the chord you want to aim at, call its root a temporary tonic, then build a major triad or dominant seventh chord a perfect fifth above that root, exactly the way you would build V or V7 in any key. That new chord almost always needs a note borrowed from outside the home key signature, because a real dominant needs a leading tone a half step below its temporary tonic, and the home key's own scale rarely supplies that exact half step naturally.

That borrowed note is the whole point. It is what separates a secondary dominant from a chord that merely shares a root or shares scale tones with something already in the key. The accidental creates a leading-tone pull that the plain diatonic chord never had, aiming the ear toward the target chord the way a normal dominant aims toward tonic. Label these chords by naming the dominant function and the target: V7 of IV, V of vi, V7 of ii, and so on.

This spelling move is the seed of modulation. Once a secondary dominant resolves to its target chord, that target can start acting like a real tonic if the music stays there and keeps reinforcing it with its own dominant. Secondary leading-tone chords, built the same way but as leading-tone triads or seventh chords above the temporary tonic, work alongside secondary dominants and get covered right after this. Spelling both correctly, half step by half step, is what makes the later work on resolution and modulation possible.

Key terms

secondary dominant
A major or dominant seventh chord built on the fifth scale degree above a chord other than the tonic.
temporary tonic
The target chord being treated, just for that moment, as if it were the key's true tonic.
leading tone
The note a half step below a temporary tonic that creates the pull toward it.
accidental
A note altered with a sharp, flat, or natural sign that is not part of the home key signature.
V7 of IV
The secondary dominant seventh chord built a fifth above the home key's fourth scale degree, pulling toward IV.

Watch it explained

  1. How it worksHow do you build a secondary dominant by treating the target chord's root as a temporary tonic?
  2. Worked exampleWalk me through spelling the V7 of IV chord in G major and explaining its one accidental.
  3. Worked exampleFind the V of vi chord and the V7 of ii chord in F major with all their accidentals.
  4. Common mistakeWhy isn't the V of IV chord in a major key just the tonic triad written another way?

Check yourself

Your turn1 of 2
A secondary dominant is built by treating the target chord's root as a temporary tonic and stacking a major third above it. If the target chord's root sits 6 half steps above middle C, how many half steps above middle C is the secondary dominant's third, a major third, four half steps, above that root?

End of topic.

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