The
triad built on the supertonic note is called the supertonic chord. In
Roman numeral analysis, the supertonic chord is typically symbolized by the Roman numeral "ii" in a major
key, indicating that the chord is a
minor chord (in C: D–F–A). In a minor key, it is indicated by "iio" if it is built on the a
natural minor scale, indicating that the chord is a
diminished chord (in C: D–F–A♭). Because it is a diminished chord, it usually appears in
first inversion (iio6) so that no note
dissonates with the
bass note.
These chords may also appear as
seventh chords: in major, as ii7 (in C: D–F–A–C), while in minor as iiø7 (in C: D–F–A♭–C) or rarely ii7. They are the second-most-common form of
nondominant seventh chords.[2]
The supertonic chord normally functions as a
predominant chord, a chord that naturally resolves to chord with
dominant function. The supertonic chord lies a
fifth above the V chord. Descending fifths are a strong basis for harmonic motion (see
circle of fifths). The supertonic is one of the strongest predominants and approaches the V chord from above by descending fifth.
In C major: A Neapolitan sixth chord in first inversion contains an interval of a sixth between F and D♭Common-tone diminished seventh chord resolving to I 6
In major or minor, the major chord built on the lowered supertonic (♭) is called a
Neapolitan chord (in C: D♭–F–A♭), notated as N6 or ♭II6, usually used in first inversion. The supertonic may be raised as part of the
common-tone diminished seventh chord, ♯iio7 (in C: D♯–F♯–A–C). One variant of the supertonic seventh chord is the supertonic diminished seventh[3] with the raised supertonic, which equals the lowered third through
enharmonic equivalence (in C: D♯=E♭).
The term supertonic may also refer 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.