Augmented sixth chord
In music theory, an augmented sixth chord contains the interval of an augmented sixth, usually above its bass tone. This chord has its origins in the Renaissance, was further developed in the Baroque, and became a distinctive part of the musical style of the Classical and Romantic periods.
Conventionally used with a predominant function, the three more common types of augmented sixth chords are usually called the Italian sixth, the French sixth, and the German sixth.
Augmented sixth interval
The augmented sixth interval is typically between the sixth degree of the minor scale,, and the raised fourth degree,. With standard voice leading, the chord is followed directly or indirectly by some form of the dominant chord, in which both and have resolved to the fifth scale degree,. This tendency to resolve outwards to is why the interval is spelled as an augmented sixth, rather than enharmonically as a minor seventh.Although augmented sixth chords are more common in the minor mode, they are also used in the major mode by borrowing of the parallel minor scale.
Types
There are three main types of augmented sixth chords, commonly known as the Italian sixth, the French sixth, and the German sixth.Though each is named after a European nationality, theorists disagree on their precise origins and have struggled for centuries to define their roots, and fit them into conventional harmonic theory. According to Kostka and Payne, the other two terms are similar to the Italian sixth, which, "has no historical authenticity- simply a convenient and traditional label."
Italian sixth
The Italian sixth is derived from iv6 with an altered fourth scale degree,. This is the only augmented sixth chord comprising just three distinct notes; in four-part writing, the tonic pitch is doubled.The Italian sixth is enharmonically equivalent to an incomplete dominant seventh. VI7=V7: A, C, G.
French sixth
The French sixth is similar to the Italian, but with an additional tone,. The notes of the French sixth chord are all contained within the same whole tone scale, lending a sonority common to French music in the 19th century.This chord has the same notes as a dominant seventh flat five chord and is in fact the second inversion of II75.
German sixth
The German sixth is also like the Italian, but with an added tone,.In Classical music, however, it appears in much the same places as the other variants, though perhaps less often because of the contrapuntal difficulties outlined below. It appears frequently in the works of Beethoven, and in ragtime music. The German sixth chord is enharmonically equivalent to a dominant seventh chord though it functions differently.
Avoiding parallel fifths
It is more difficult to avoid parallel fifths when resolving a German sixth chord to the dominant chord. These parallel fifths, referred to as Mozart fifths, were occasionally accepted by common practice composers. There are two ways they can be avoided:Other types
Other variants of augmented sixth chords can be found in the repertoire, and are sometimes given whimsical geographical names. For example: 4–6–7–2; is called by one source an Australian sixth. Such anomalies usually have alternative interpretations.Function
Standard function
From the Baroque to the Romantic periods, augmented sixth chords had the same harmonic function: as a chromatically altered predominant chord leading to a dominant chord. This movement to the dominant is heightened by the semitonal resolution to from above and below ; 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, 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, and, rather than just.
In most occasions, the augmented-sixth chords precede either the dominant, or the tonic in second inversion. The augmented sixths can be treated as chromatically altered passing chords.
Other functions
In the late Romantic period and other musical traditions, especially jazz, other harmonic possibilities of augmented sixth variants and sonorities outside its function as a predominant were explored, exploiting their particular properties. An example of this is through the "reinterpretation" of the harmonic function of a chord: since a chord could simultaneously have more than one enharmonic spelling with different functions, its function could be reinterpreted mid-phrase. This heightens both chromaticism by making possible the tonicization of remotely related keys, and possible dissonances with the juxtaposition of remotely related keys.Tchaikovsky considered the augmented sixth chords to be altered dominant chords. He described the augmented sixth chords to be inversions of the diminished triad and of dominant and diminished seventh chords with a lowered second degree, and accordingly resolving into the tonic. He notes that, "some theorists insist upon resolution not into the tonic but into the dominant triad, and regard them as being erected not on the altered 2nd degree, but on the altered 6th degree in major and on the natural 6th degree in minor", yet calls this view, "fallacious", insisting that a, "chord of the augmented sixth on the 6th degree is nothing else than a modulatory degression into the key of the dominant".
The example below shows the last nine measures from Schubert's Piano Sonata in A major, D. 959. In m. 352, an Italian sixth chord built on scale degree functions as a substitute for the dominant.
Inversions
Augmented sixth chords are occasionally used with a different chord member in the bass. Since there is no consensus among theorists that they are in root position in their normal form, the word "inversion" isn't necessarily accurate, but is found in some textbooks, nonetheless. Sometimes, "inverted" augmented sixth chords occur as a product of voice leading.Rousseau considered that the chord could not be inverted. Seventeenth century instances of the augmented sixth with the sharp note in the bass are generally limited to German sources.
The excerpt below is from J.S. Bach's Mass in B minor. At the end of the second measure, the augmented sixth is inverted to create a diminished third or tenth between the bass and the soprano ; these two voices resolve inward to an octave.
Related chords
In music theory, the double-diminished triad is an archaic concept and term referring to a triad, or three note chord, which, already being minor, has its root raised a semitone, making it "doubly diminished". However, this may be used as the derivation of the augmented sixth chord. For example, F–A–C is a minor triad, so F–A–C is a doubly diminished triad. This is enharmonically equivalent to G–A–C, an incomplete dominant seventh A, missing its fifth), which is a tritone substitute that resolves to G. Its inversion, A–C–F, is the Italian sixth chord that resolves to G.Classical harmonic theory would notate the tritone substitute as an augmented sixth chord on 2. The augmented sixth chord can either be an It+6 enharmonically equivalent to a dominant seventh chord ; a Ger+6 equivalent to a dominant seventh chord with ; or a Fr+6 equivalent to the Lydian dominant, all of which serve in a classical context as a substitute for the secondary dominant of V.
All variants of augmented sixth chords are closely related to the applied dominant V7 of II. Both Italian and German variants are enharmonically identical to dominant seventh chords. For example, in the key of C, the German sixth chord could be reinterpreted as the applied dominant of D.
Simon Sechter explains the chord of the French sixth chord as being a chromatically altered version of a seventh chord on the second degree of the scale,. The German sixth is explained as a chromatically altered ninth chord on the same root but with the root omitted.
The tendency of the interval of the augmented sixth to resolve outwards is therefore explained by the fact that the A, being a dissonant note, a diminished fifth above the root, and flatted, must fall, whilst the F – being chromatically raised – must rise.
Relationship between the different types
The following "curious chromatic sequence", graphed by Dmitri Tymoczko as a four-dimensional tesseract, outlines the relationships between the augmented sixth chords in 12TET tuning:- Starting with a diminished seventh chord, lower any factor by a semitone. The result is equivalently to a German sixth chord.
- From the German sixth chord, lower any factor by a semitone so that the result is ancohemitonic. The result is a French sixth chord or minor seventh chord possibly posing as a virtual augmented sixth.
- From the French sixth chord, there exists a factor which, when lowered by semitone, gives a result equivalent to a half-diminished seventh chord possibly posing as a virtual augmented sixth.
- From the half-diminished seventh chord as augmented sixth, there exists a factor which, when lowered by a semitone, is equivalent to a diminished seventh chord at the interval one semitone lower than the diminished seventh chord which started the sequence.
- Three repetitions of the above complete the cycle in modulo-12 note space, forming a necklace of three tesseracts joined at opposite corners by diminished seventh chords and subsuming all 12 notes of the chromatic scale.
Minor seventh as virtual augmented sixth chord