In music theory, an augmented seventh is an interval that has twelve half steps 
The augmented seventh requires that:
- The interval must be a seventh interval (seven note names between the first and the last).
- The interval must have twelve half steps.
What does an augmented seventh look like?
Here is an example of a melodic augmented seventh (two music notes in a melody) and a harmonic augmented seventh (in a chord):
How to recognize an augmented seventh?
Rule of music theory: All intervals in a major scale starting with the tonic (degree I) are either major or perfect, and only unison, octave, fourth and fifth are perfect (the others are major).
Example with the interval A♭ / G♯:
Let's take the A flat major scale to have A♭ as the tonic:
From the rule stated above, the interval A♭ / G♮ is a major seventh, so the interval A♭ / G♯ is an augmented seventh.
Inversion of the augmented seventh
We can consider that the inversion of the augmented seventh does not exist.
Musical examples of augmented seventh
No examples yet, but feel free to send me some examples!
Interval identification game
You will find this interval in my Intervals identification game: