In music or music theory, the supertonic is the second degree of the diatonic scale, or a chord with the second scale degree as its root. For example, in the C major scale the supertonic is the note D. The supertonic triad uses the notes D, F, and A. In music theory, the supertonic chord is symbolized with the Roman numeral II if major or ii if minor.
In major keys the supertonic chord is a minor triad; in minor keys it can either be minor or diminished, depending on the type of minor scale used. The supertonic shares two notes with the subdominant chord (F and A in the key of C). Due to this close relationship, a supertonic chord is often used as a substitute for the subdominant. Adding an additional interval of a third on top of the triad results in a “seventh chord:” D – F – A – C, which is commonly used in jazz music.