Augmented Sixth Chord - Standard Harmonic Function

Standard Harmonic Function

From the Baroque to the Romantic period, augmented sixth chords have had the same harmonic function: as a chromatically altered predominant chord (typically, an alteration of ii, IV, vi7 or their parallel equivalents in the minor mode) leading to a dominant chord. This movement to the dominant is heightened by the semitonal resolution of both ♭6 to 5 and ♯4 to 5; essentially, these two notes act as leading-tones. This characteristic has led many analysts to compare the voice leading of augmented sixth chords to the secondary dominant V of V because of the presence of ♯4, the leading-tone of V, in both chords. In the major mode, the chromatic voice leading is more pronounced because of the presence of two chromatically altered notes, ♭6, as well as ♯4, rather than just ♯4 in the minor mode.

During the Romantic period, the augmented sixth harmony increased in ambiguity as composers explored other functional possibilities outside of its role as a predominant. See #Extended functions.

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