2.5 Summary

Secondary chords let you add an interesting, unfamiliar sound to your song. Below is a summary of some of the important concepts you learned in this chapter.

• Secondary chords briefly emphasize a chord other than I as home base. The most common secondary chord is when the chord functions as the V of another chord. These secondary chords are known as secondary dominants and are labeled as V/X (read “V of X” where X can be any of the basic chords).
• V/V is built off scale degree 2; it contains scale degrees 2, ♯4, and 6. In the key of C, this corresponds to a D major chord.
• Because V/V chords have a ♯4 in them (D major chords contain an F♯), they contain notes outside the key. As a major chord, V/V has a brighter sound that contrasts with the expected minor chord built off scale degree 2. V/V usually goes to V (reflecting its main function).
• V/IV is built off scale degree 1; it contains scale degrees 1, 3, and 5. In the key of C major, this corresponds to a C major chord, which is no different from a I chord. The difference shows up when the chord is made a seventh chord and becomes a dominant seventh instead of a major seventh chord. For this reason, V/IV is almost always seen as V⁷/IV → IV.
• V/vi is built off scale degree 3. It contains scale degrees 3, ♯5, and 7, and usually resolves to the vi chord.
• When inverting secondary chords, there is a chance that a scale degree outside of the major scale will show up in the bass. When this happens, these inverted secondary chords can be used to bridge neighboring chords by connecting their bass lines, e.g., V → V⁶/vi → vi ( 5 → ♯5 → 6), and I → V⁴₂/IV → IV⁶ (1 → ♭7 → 6).
• vii° doesn’t show up very often on its own, but it is common as a secondary chord. vii°/vi is most common and often is used to quickly pass between V and vi.
• IV/IV is another secondary chord common in popular music. IV/IV goes to IV and then often proceeds to I to end the progression.