Augmented sixths are a way of emphasising the arrival on the dominant. The key feature is the dissonant augmented sixth (here Eb – C#) which resolves outwards onto the root of the next chord top and bottom.
The augmented sixth interval is in the left hand this example. The music uses the augmented sixth to help emphasize a modulation of G minor.
How to write an augmented sixth
NOTE: the voice-leading is very important to the augmented sixths. The bass progression must be as in step 8 and the augmented sixth above it (which does not have to be at the top but must not be below the bass in any part) must resolve upwards by step.
- decide on the chord to which your augmented sixth will resolve
in this example a C major chord (V of F)
- write down the note above the root of this chord
in this example a D – one note above C
- flatten or natural this note so that it is a semitone above the note it will resolve to
in this example the D needs a flat
- write down the note below the root of the original chord (an octave up)
in this example a B – one note below C
- if necessary, natural or sharpen this note so that it is semitone below the note it will resolve to
not necessary in this example
- add a major third to the chord to make an Italian augmented sixth
- add an additional augmented fourth to make a French sixth or a perfect fifth to make a German sixth the top and bottom notes must resolve up and down a semitone respectively