Sixte ajoutée

What it means

Sixte ajoutée — “added sixth” — designates a triad to which the sixth is added above the fifth, without a seventh joining it. In C major, the subdominant with an added sixth yields the notes F, A, C, and D. The term comes from eighteenth-century French harmonic theory.

Musical use

The sixth reinforces the subdominant character and prepares the dominant; the sonority is designated as S with an appended 6. The interpretation is not uncontested: the same sonority can also be understood as the six-five chord of a seventh chord on the second degree, and theory has discussed both readings. In function theory the interpretation as a subdominant with an added sixth predominates, in scale-degree theory that as an inversion.

A second, quite different use is the sixth on the tonic triad as a closing sonority. Here it is not resolved but remains standing as a colour, and the close thereby seems soft and open rather than concluded. In the music around 1900, in jazz, and in popular music, the tonic sonority with a sixth is widespread; in jazz it belongs among the common chord symbols.

The added sixth is to be distinguished from the seventh: the seventh makes the chord dissonant and demands resolution, the sixth forms a consonant combined sound with the other notes and can remain standing.

The term was coined by Jean-Philippe Rameau in the eighteenth century. The chord is identical in pitch with the six-five chord of the second degree; whether one interprets it as a subdominant with a sixth or as a seventh chord on the second degree is a question of theory. In jazz and in popular music, the six-three chord often stands as the tonic sonority at a close.

Performance practice

Determine from the context whether the sixth prepares a subdominant or colours a close — in the first case the sonority leads to the dominant, in the second it rests. Set the sixth on top, so that the sonority stays transparent. And take it softly in the closing chord; it is colour, not tension.