Supertonic

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In music or music theory, the supertonic is the second degree or note of a diatonic scale (in other words, immediately "above" the tonic). For example, in the C major scale (white keys on a piano, starting on C), the supertonic is the note D; and the supertonic chord uses the notes D, F, and A. In music theory, the supertonic chord is symbolized by the Roman numeral II if major (for example D-Fmusic|#-A in the C Lydian mode) or ii if minor (for example D-F-A in C major without any chromatic alteration).

The function of the supertonic chord in a tonal/functional context is to either establish the dominant as a secondary tonic, the supertonic being the dominant of the dominant or V/V, or to progress to the Dominant either as a part of sectional form or part of a chord progression such as the circle of fifths (V/V-V-I, in C: D-G-C). When spelled diatonically, the supertonic is a minor triad in a major key, and a diminished triad in a minor key.

"Supertonic" also refers to a relationship of musical keys. For example, relative to the key of C major, the key of D major (or D minor) is the supertonic. Modulation (change of key) to the supertonic is relatively common (by far the most common modulation in modern popular music), Fact|date=June 2008 though in classical music it is more common to modulate to the dominant or other keys.

In German theory derived from Hugo Riemann the supertonic is considered the subdominant parallel: Sp/T in major and sP/T in minor.