What is the interval for an augmented sixth in music theory?

An augmented sixth interval is defined as an interval that spans six diatonic scale degrees while increasing the distance between two notes to create a specific augmented effect. Within the context of augmented sixth chords, such as the Italian, French, and German augmented sixths, the interval itself is integral to their harmonic function, particularly in leading to the dominant chord.

The correct choice identifies the interval as an augmented sixth and a major second. This accurately captures the essence of the augmented sixth, which is critical for creating tension that resolves to the dominant. The presence of a major second in conjunction with the augmented sixth is characteristic of the voicing used in these chords, particularly in the French augmented sixth which often includes the interval of a second alongside the augmented sixth.

Understanding that the augmented sixth resolves outward to the octave of the tonic is vital in music theory, emphasizing the functional aspect of this interval in harmonic progressions. This resolution is foundational in Western tonal harmony, providing both a dramatic tension and a clear resolution that is essential in the movement toward a dominant chord.