Structurally speaking, an augmented chord consists of stacked major 3rds. So the chord C Aug (C+) uses the notes C-E-G#. It could occur naturally in a minor key song that uses the harmonic minor scale. But it far more likely occurs in major keys, where the added accidental (the G# in the C+ chord) creates an altered chord.
The most common way to use a C+ (augmented) chord is to consider the E to be a leading tone, wanting to move up to the root of an F major chord: C+ –> F. [LISTEN] (Opens in a new window/tab)
In that sense, it’s also possible to consider either of the other two notes of the C+ as leading tones. That’s because all three tones of the chord are the sasme distance from each other. That means that C+ can be followed by a Db major chord, or an A major chord. It might be considered more common, in those cases, to rename the same chord to be either E+ or G#+. All three chords (C+, E+, G#+) will all have the same three notes.
Here are some chord progressions that use C+, E+ and G#+ in various ways:
C C+ F G7 C
C Am E+/G# Am F C Dm G C
Db Ab Db Ab+ Db Gb Absus4 Ab Db
Am E+ Am G C
F Bb C C+ F
Written by Gary Ewer. Follow Gary on Twitter