Dominante Secundária

Secondary dominants: rule and example

A secondary dominant is a dominant-seventh chord that resolves to some other diatonic chord rather than the tonic, briefly "tonicizing" that chord. The notation V7/V ("five of five") just means the V7 of whichever chord normally acts as V. Take C major: V7/V = D7 (resolves to G), V7/IV = C7 (resolves to F), V7/ii = A7 (resolves to Dm), and V7/vi = E7 (resolves to Am). The chord brings in harmonic color, but the key stays put.

Context and applications

You'll find secondary dominants all over bossa nova, jazz, and pop. The Beatles' "Here Comes the Sun" reaches for V7/V during the "sun, sun, sun..." bridge. Tom Jobim's writing (Garota de Ipanema, Wave) leans hard on V7/ii and V7/vi. In jazz the II–V–I framework stretches out with secondary dominants into extended cycles, since any chord can be approached by its own V7. When you analyze MPB, choro, or Great American Songbook standards, labeling and arranging really comes down to catching these tonicizations.

FAQ

Does a secondary dominant modulate the key? No. It tonicizes the target chord for a beat or a measure, and then the original key picks right back up.

How do I build V7/X? Start from the root of X, go up a perfect fifth, and stack a dominant 7th (1, 3, 5, ♭7) on the note you land on.

What is the tritone substitute? Swapping V7/X for the dominant 7th a tritone away (say, D7 → A♭7 before G). It's a jazz staple.

Why does V7/IV sound bluesy in major? Because it brings in the ♭7 of the tonic (C7 in C major holds a B♭), which is the very note that gives the blues scale its character.