Augmented sixth chord.

A chord built normally on the flattened submediant and containing the note an augmented 6th above (i.e. the raised subdominant): in C major, A– F. The normal resolution of this interval is outwards to the octave; thus an augmented 6th chord characteristically resolves to the chord of the dominant or to a I6-4 chord. The character of an augmented 6th chord is largely determined by the other notes it contains. The simplest type, commonly (but arbitrarily) called the Italian 6th chord, has a major 3rd above the flattened submediant and resolves more easily to the dominant (ex.1a). The so-called French 6th chord has both a major 3rd and an augmented 4th and therefore also resolves more easily to the dominant (ex.1b); it also contains more of the flavour of the whole-tone scale. The so-called German 6th chord has a major 3rd and a doubly augmented 4th or a perfect 5th and naturally resolves to I6-4 or V, being spelt accordingly (ex.1c–d); the latter resolution creates a type of consecutive 5ths called ‘Mozart’ 5ths (see Consecutive fifths, consecutive octaves). In equal temperament the German 6th sounds like a dominant 7th chord, and therefore it can resolve ‘deceptively’ on to the chord of the flattened supertonic, or ‘Neapolitan sixth’ chord (ex.1e).

See also Harmony.

WILLIAM DRABKIN