The tritone between \hat1 and # \hat4 is another characteristic dissonance of all augmented sixth sonorities. In Example 32–2, for instance, we see that raising the root of a iv 6 chord creates an augmented sixth with the bass. They retain that function and most commonly lead to the dominant. Augmented sixth sonorities invariably include scale degree \hat1-a major third above the bass-which moves to the leading tone in the ensuing dominant harmony.Īs Example 32–2 demonstrates, augmented sixth sonorities may arise from chromatic alterations of pre-dominant chords. Example 32–2c fills out the sonority with an inner voice. Now both voices are only a semitone away from their respective destinations. Raising scale degree \hat4, as in Example 32–2b, will produce an augmented sixth. Here, the lower voice descends to \hat5 by semitone while the upper voice ascends by whole tone to the same scale degree. (See Chapter 12 for more on how basic interval progressions lie at the base of all voice-leading.)Įxample 32–2a shows the familiar basic interval progression of a major sixth expanding to an octave, as it might appear in the common progression iv 6–V (in this case, in A minor). 32.2 Structure and derivationĪugmented sixth sonorities are derived by chromatically altering a common basic interval progression.
We will then examine several complex uses of this type of sonority. Like other chromatic sonorities, augmented sixths can have a striking effect that composers exploit in order to heighten dramatic tension or highlight important structural moments.Īfter discussing the general structure and derivation of augmented sixth sonorities, we will look at the three common types and their function in tonal music. As seen in Example 32–1, augmented sixth sonorities characteristically function as pre-dominant chords and usually lead to dominant harmony. As you will see in this chapter, there are several types of chromatic sonorities characterized by the presence of an augmented sixth, appropriately referred to as augmented sixth sonorities. Nevertheless, chromatic sonorities containing an augmented sixth appear quite frequently. No two diatonic pitches will produce an augmented sixth. Of course, this type of sonority could never occur diatonically. The only difference between these notes and a typical leading tone is that in this case one of the notes (A b) moves in the opposite direction. We may think of them as dual leading tones to scale degree \hat5, since each approaches its destination with half-step motion. Just as a leading tone lies a half step away from the tonic, A b and F # both lie a half step away from G. As the sonority moves to V in the following measure, we see that the outer voices both resolve outward by semitone to G. 4, the outer voices expand in contrary motion to form an augmented sixth (A b in the bass with F # in the treble).
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