“Aug” stands for augmented and in a triad augmented chord there is the root and two major thirds. These chords are quite uncommon and their function is mostly to be placed between two chords that lack distinct relationship.
See diagrams of aug chords:
An aug chord will often sound dissonant. The reason is that one of the three notes in the triad is not included in the same key as the root note. Gaug, for example, consist of the notes G, B and D#, among which only G and B are part of the G major scale.
There are two categories of augmented chords.
Comparing the C Major Chord with Caug and Caug7:
C: C – E – G
Caug: C – E – G#
Caug7: C – E – G# - A#
The only difference between C major and C augmented triads is that the fifth is raised, or augmented, one semi-step. The augmented seventh chord adds a minor seventh. It is, however, not as common to write these chords aug7 as +7 or 7#5 (even the less correct 7+ occur).
The formula for the aug chord is 1 - 3 - #5. There are four half steps to the 2nd note and four half steps to the 3rd.
Besides the aug chord name that is used on this site, you may find the alternative plus symbol (+), as in C+, being used occasionally. A third symbol that occurs less commonly is C(#5) instead for Caug ("#5" indicates that the fifth is sharpenedThe tone is one half step higher).
And the most important part: how and when to use augmented chords? They are often used as passing notes, meaning that they are placed between two chords that have stronger relationship with the key. One way is to create a feeling of movement by a small shift from the tonic chord to an aug version of it and when go one half-step up from its major fifth and use that as the root for the next chord. This can be seen below in both sequences.
Chord sequences that shows how aug chords can be utilized:
1. C Caug Am
2. G Gaug Em
(The intervals are the same: I I+ vi.)
Major chords Minor chords Seventh chords Extended chords Sus chords Dim chords Aug Chords Add Chords Altered Chords