Secondary Dominants
A chord doesn't have to be the tonic to get its own dominant. Secondary dominants briefly borrow a V chord from another key to make any diatonic chord feel like a temporary "home."
What is a secondary dominant?
In any key, only one chord gets a "real" dominant: the tonic, whose dominant is V. But every other diatonic chord can be treated as a momentary tonic too — and just like a real tonic, it can get its own dominant chord borrowed from its own key. That borrowed dominant is called a secondary dominant, and the brief, local pull it creates toward its target chord is called tonicization.
Secondary dominants are notated with a slash: V/V ("five of five") is the dominant of the V chord. V7/ii is the dominant 7th of the ii chord. Read the slash as "of" — the numeral on the left is a dominant, and the numeral on the right is the temporary tonic it's aimed at.
Building one: a perfect 5th below the target
To spell any secondary dominant, find your target chord's root, then build a major triad (or dominant 7th) a perfect 5th below it — the same root relationship as V sits below I in any key. In C major, the diatonic ii chord is D minor. A perfect 5th below D is A, so V/ii is an A major (or A7) chord, which resolves down a 5th into D minor exactly like a real V–I cadence.
Why it works: a mini V–I in disguise
Every secondary dominant contains its own tritone between its 3rd and 7th, exactly like a real V7 chord — that's what makes the pull toward the target chord feel so strong even though the target isn't the actual tonic. Your ear briefly accepts the target chord as "home," which is why this technique adds so much forward motion without ever leaving the key for long.
Common questions
What is a secondary dominant?
A dominant chord borrowed from the key of a diatonic chord other than the tonic, used briefly to make that chord feel like a temporary tonic — a process called tonicization.
What does V/V mean?
"Five of five" — the dominant chord of the V chord's own key. In C major, V is G major, and the dominant of G is D major, so V/V is a D major (or D7) chord that resolves to G.
How do you spell a secondary dominant?
Build a major triad or dominant 7th chord a perfect 5th below the target chord — the same root relationship as V to I in any key.
Do secondary dominants have to resolve to their target chord?
Not strictly, but the strong pull toward the target is exactly why they're used, and most of the time they do resolve as expected.
Hear chromatic harmony in any key
Melody Monkey's Songwriting Studio lets you drop in secondary dominants and hear them resolve instantly, in any key.
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