Secondary dominants are one of the most powerful tools in song construction. They allow you to step outside the strict boundaries of a single key to create temporary tension, propel your chord progressions forward, and make predictable harmonic movements sound sophisticated and intentional.

Here is your guide to understanding and using secondary dominants on the guitar.

1. What Is a Secondary Dominant?

To understand a secondary dominant, you first need to look at primary dominant chords in diatonic harmony.

In any major key, every scale degree builds a specific chord. The chord built on the 5th degree (represented by the Roman numeral V or V7) is called the primary dominant. Its primary function is to resolve smoothly back home to the I chord (the tonic).

• Example in the Key of C Major:

  • I = C

  • dm = ii

  • em = iii

  • F = IV

  • G7 = V7 (Primary Dominant)

  • am = vi

The G7 chord naturally wants to pull back to C.

A secondary dominant applies this same tension-and-resolution principle to other non-tonic chords within the key. Instead of resolving to I, a secondary dominant target-resolves to a secondary chord (such as the ii, iii, IV, V, or vi).

2. How Secondary Dominants Work

To build a secondary dominant, locate the chord you want to target, treat that target chord as if it were a temporary tonic (“key of the moment”), and play the V7 chord from that target’s native key.

Because secondary dominants introduce a note outside of the home key (called an accidental), they immediately catch the listener’s ear and create momentum toward the target chord.

Notation: $V7/X$

Secondary dominants are written as $V7 / [Target]$. For instance:

• $V7/ii$ means “the 5th dominant chord of the 2nd degree.”

• $V7/V$ means “the 5th dominant chord of the 5th degree.”

3. Secondary Dominants in the Key of C Major

Here is a breakdown of the secondary dominants available in C Major and where they naturally lead:

4. Practical Guitar Application: Comparing Progressions

The best way to feel the effect of a secondary dominant is to hear a standard diatonic progression compared directly to one using a secondary dominant.

Standard Diatonic Progression (Key of C)

A very common pop/rock progression moving I – vi – ii – V:

| C | Am | Dm | G7 |

While smooth, this progression can feel predictable.

Upgraded with $V7/ii$ (A7)

By inserting the secondary dominant of Dm (A7) right before the Dm chord, you create a strong chromatic voice-leading line (the C note in C changes to C# in A7, which then resolves to D in Dm):

| C | A7 | Dm | G7 |

Tab Comparison

Standard Diatonic Transition (Am to Dm):

   Am               Dm
e |--0-----------|--1-----------|
B |--1-----------|--3-----------|
G |--2-----------|--2-----------|
D |--2-----------|--0-----------|
A |--0-----------|--------------|
E |--------------|--------------|

Secondary Dominant Transition (A7 to Dm):

   A7               Dm
e |--0-----------|--1-----------|
B |--2-----------|--3-----------|
G |--0-----------|--2-----------|
D |--2-----------|--0-----------|
A |--0-----------|--------------|
E |--------------|--------------|

Notice how the middle finger moving to the C# on the B-string creates an irresistible pull upward to the D note on the next chord.

5. Key Takeaways for Songwriting

• Target Any Diatonic Chord: You can place a secondary dominant in front of almost any major or minor chord in a key (except the vii° diminished chord).

• Look for Chromatic Voice Leading: The non-diatonic note inside the secondary dominant usually sits just a half-step away from a note in your target chord. Highlight that half-step movement on the fretboard.

• Use Sparingly: Secondary dominants provide the most impact when used at key structural moments, such as leading into a verse-to-chorus transition or driving toward a turnaround.