An '''augmented sixth chord''' is a [[chord (music)|chord]] whichdefined often hasby the [[interval (music)|interval]] of an [[augmented sixth]] between itstwo highestof and lowestit's notes. For example, an Italian augmented-sixth chord (with an A flat in the bass) consists of the notes (from the bottom up) A flat, C, F sharp. All augmented-sixth chords arefunction as subdominant chords, and can be understood as altered inversions of taxonomic subdominantsub-dominant function chords (II and IV) within some diatony.
Here are the four most common "sixth" chords (though there are more than these found in the literature):
