Added tone chord

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An added tone chord is a triad with one or more extra notes added. The added note is not a seventh. These notes can appear outside the normal stack of thirds, such as add4, add6, add2, or add9. If the added tone is in the bass, the chord is usually written as a slash chord (for example, Cadd2/D becomes C/D).

Common types
- Add2 and Add9: a major or minor triad with a second or ninth above the root. They’re the same pitch class, just voiced differently.
- Add4: the triad plus a perfect fourth above the root. This often happens on the dominant chord and can lead nicely to the tonic.
- Add6: the triad plus a sixth above the root. It shares notes with a seventh chord a minor third down (for example, C6 has the same notes as Am7).
- Add13 (often discussed with add6): a sixth combined with a thirteenth feel, used in some styles.
- 6/9: a major triad with both a sixth and a ninth, used as a relaxing substitute for the tonic in jazz.
- Minor 6/9: a minor triad with a sixth and a ninth, creating a Dorian-like flavor.
- Mixed (split) thirds: chords that include both a major and a minor third (for example, C–E♭–E–G). These can sound colorful or dissonant and are common in blues, rock, and some pop music.
- Dominant 7 with sharp 9 (7♯9): a dominant seventh chord with a raised ninth (for example, 7♯9). The sound is edgy and iconic in songs like Purple Haze and Boogie Nights.
- The mu chord: a notable add2 voicing popularized by Steely Dan.

Inversions and voicings
- When the added tone is in the bass, you’ll often see slash chords (C/D, for example) instead of an “add” label.

How these chords are used
- Added tone chords add color and tension without fully changing the chord’s basic feel.
- They’re often used as stronger substitutes for traditional chords or to suggest different tonal flavors without introducing new chord functions.