augmented 6th chords

In music, a group of chords that stand as the springboard for much of the more colourful harmonic style of the 19th century. They depend for their effect on the interval of an augmented 6th between the flattened 6th degree and the sharpened 4th degree of the diatonic scale. Almost invariably their logical progression is to the dominant (V) or to a second inversion triad on the dominant (I64) which in turn leads to the dominant.

Of the four-note forms, the ‘German 6th’ first became a firm favourite at the end of the 18th century and was used with particular force by Beethoven. Less common is the ‘French 6th’, with its two middle notes a major 2nd apart. Finally, it may be noted that from the middle of the 19th century many other variants of the principle appear.