Secondary Dominants: The Secret Sauce in Jazz Harmony

Let me guess… you’ve been playing through a jazz standard and suddenly — BAM! — a dominant 7th chord pops up that doesn’t belong.

No, your Real Book isn’t wrong. You’ve just met one of my favorite little tricks in harmony: the secondary dominant.

These sneaky guys are all over jazz. They add movement, a bit of harmonic “oomph,” and they make your ears go, “ohhh yeah, that’s nice.”

Today we’re going to:

• Demystify what secondary dominants are

• Show you how to spot them in seconds

• Give you guitar-friendly voicings and ways to practice them

So… What Is a Secondary Dominant?

You already know the main V7 chord in a key — in C major, that’s G7. It’s the boss. The one that resolves to the I chord (Cmaj7) and makes you feel at home again.

A secondary dominant is just another V7 chord that temporarily treats a different chord like it’s “the home.”

Think of it as:

• Normal dominant: “Let’s go home.”

• Secondary dominant: “Let’s go to their house first — it’s on the way, and they have snacks.”

Example in C major:

| Cmaj7 | A7 | Dm7 | G7 | Cmaj7 |

• A7 isn’t in C major.

• But A7 resolves to Dm7 (down a fifth).

• Voilà: A7 is V7/ii (“five of two”).

Why This Works So Well

It’s all about momentum. Dominant chords pull. And when you aim that pull at a chord that isn’t the tonic, you get a little harmonic side-trip — without packing your bags for a full key change.

Jazz loves this because it keeps the harmony moving and gives you tasty soloing options.

The Greatest Hits of Secondary Dominants

You’ll run into these all the time:

Guitar-Friendly Voicings

Here are a few drop-in shapes you can start using right now:

V7/ii (A7 → Dm7) – Drop 2, 5th String Root

V7/V (D7 → G7) – Shell, 6th String Root

V7/vi (E7 → Am7) – Altered, 5th String Root

Spotting Them in the Wild

The checklist:

1. See a dominant 7th chord.

2. Ask yourself: “Should this even be in the key?”

3. If the answer is “no,” check the next chord.

4. If that next chord is a fifth below… boom, you’ve found your secondary dominant.

Example in G major:

| Gmaj7 | E7 | Am7 | D7 | Gmaj7 |

• E7 isn’t diatonic in G major (should be Em7).

• Am7 is a fifth below E7 → secondary dominant unlocked.

How to Practice This Stuff

Here’s my go-to drill:

• Pick a key — let’s say C major.

• Drop in three secondary dominants: V7/ii, V7/V, and V7/vi.

| Cmaj7 | A7  | Dm7 | G7  | Cmaj7 | E7  | Am7 | D7  | G7  | Cmaj7 |

Run this through:

• Comping: shell voicings, then add extensions.

• Soloing: chord tones first, then scales (Mixolydian or altered).

• Mix mode: switch between comping and soloing mid-chorus.

Pro-Level Fun

Once you’re comfortable, here are three tasty upgrades:

1. Tritone subs – A7 → Eb7

2. Altered tension – E7 → E7♯9♭13 → Am7

3. Diminished link – C#dim7 between Cmaj7 and Dm7

Secondary dominants are one of the fastest ways to sound more “jazzy” without memorizing a hundred chord subs. Spot them, understand them, and own them — they’ll keep your playing moving forward and sounding hip.

See you on the next blog,
Marc