Augmented second

In classical music from Western culture, an augmented second is an interval that, in 12-tone equal temperament, is sonically equivalent to a minor third, spanning three semitones, and is created by widening a major second by a chromatic semitone.

Augmented seconds occur in many scales, most importantly the harmonic minor and its various modes.

For example, in the scale of A harmonic minor, the notes F and G♯ form the interval of an augmented second.

This distinguishing feature of harmonic minor scales occurs as a consequence of the seventh scale degree having been chromatically raised in order to allow chords in a minor key to follow the same rules of cadence observed in major keys, where the V chord is "dominant" (that is, contains a major triad plus a minor seventh).

An augmented second is enharmonically equivalent to a minor third (Playⓘ) in 12-tone equal temperament, but this does not hold true in most tunings.