What's an easy way to find out of a chord is an Augmented 6th or Diminished 3rd?

1. How do you write augmented 6th chords?
2. How do you get augmented 6th?
3. What is the usual harmonic function of an augmented 6th chord?

How do you write augmented 6th chords?

Its interval of minor seventh (between root and seventh degree (i.e.: C–B♭ in C–E♭–G♭–B♭) can be written as an augmented sixth (C–E♭–G♭–A♯). Rearranging and transposing, this gives A♭–C♭–D–F♯, a virtual minor version of the French sixth chord.

How do you get augmented 6th?

Building an augmented sixth on other scale tones:

You can use an augmented sixth chord much like you would use a secondary dominant – it gives you another way to “pull” towards a triad in the key. For example, you might wish to pull toward the tonic (but not do it by the traditional sound of using the dominant chord).

What is the usual harmonic function of an augmented 6th chord?

Augmented sixth chords are another strategy for creating harmonic intensification with chromaticism. They are mostly used as a predominant harmony (though they can serve an embellishing function as well, see common-tone chords) and lead directly to root-position V at a cadence point.