MUS 212 Study Guide H (Chapter 8)

Augmented Sixth Chords

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Italian 6th:  It6 French 6th:  Fr6 German 6th:  Gr6
  1. There is no plausible explanation for the above designations--Italian, French, German--in regard to augmented sixth chords.
  1. Augmented 6ths are chords that have been altered to include the interval of an augmented 6th. These chords are descendants of altered supertonic and subdominant chords:
  • Italian:  Spell iv.  Place the chord in first inversion.  Raise 4 one half step.
  • French: Spell ii7.  Place the chord in second inversion.  Raise 4 one half step.
  • German: Spell iv7.  Place the chord in first inversion.  Raise 4 one half step.
  1. The bass note is most frequently a M3rd below the tonic.

  1. The three most common types of augmented 6th chords (pitches added above the bass note):

  • It6 = M3rd + Aug. 6th (3-note chord),

  • Fr6 = M3rd + Aug. 4th + Aug. 6th (4-note chord),

  • Gr6 = M3rd + Per. 5th + Aug. 6th (4-note chord).

  1.  All three types have three notes in common.  In each case, 6 is raised.
  1. All three augmented 6th chords are spelled the same in parallel major and minor keys.  (Note Gr6 alternate spelling later in No. 20.)  In major keys, more accidentals are required for augmented 6th spellings.
  1. Only the major keys with signatures of 5, 6 and 7 flats have no parallel minor key.  These can be spelled using their altered chords, iv, iv7 , and ii7.  For example, spell the Gr6 in Db major:  Bbb, Db, Fb, G. (See p. 248.)
  • There are no parallel major keys for G#mi, D#mi, A#mi.
  • There are no parallel minor keys for DbMA, GbMA, CbMA.

Progression:

  1. It6 resolves to V directly, or via tonic six-four.
  1. Fr6 resolves to V directly, or via tonic six-four.
  1. Gr6 resolves to V via the tonic six-four to avoid parallel fifths.  (Some composers change the Gr6 to an It6 before resolving to V to avoid the parallel fifths.)

Exceptions:

  1. Augmented 6th chords occasionally occur in positions other than those listed above.
  1. In rare instances, the bass note of an augmented 6th chord may be a scale degree other than the norm (M3rd below tonic).
  1. Sometimes the augmented 6th interval is inverted, creating a diminished third.
  1. In rare instances, an augmented 6th chord may include notes other than those conventionally found.

Applications:

  1. Resolution:  The bass note resolves down a half-step to the root of V.
  1. Augmented 6th to octave:  The two notes forming the +6 interval resolve outwardly (contrary motion) by half-step to an octave.
  1. To tonic six-four:  The progression from +6 chords to either of these chords is only a partial resolution.  The final resolution occurs when V is reached.
  1. Doubling:  Neither of the two notes forming the +6 is ever doubled.
  • Re the It6:  Double the tonic scale degree (3rd above the bass note).
  1. Gr6 to tonic six-four only:  To avoid parallel fifths, the Gr6 proceeds first to the tonic six-four (or to an It6) before going to V.
  1. Two spellings for Gr6:
  • In C minor, for example:  Ab, C, Eb, F# (progresses to tonic six-four).
  • In C major, for example:  Ab, C, D#, F# (progresses to tonic six-four).

In C minor, Eb progresses down to D (5th of V).  In C major, Eb progressing to E natural (of tonic six-four) is considered poor spelling, so Eb is spelled D#.

  1. Stepwise movement:  Voice leading to and from an augmented 6th chord should be stepwise whenever possible--skips only when required.

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