subtonic

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"'Backdoor' ii-V" in C: ii-♭VII⁷-I Play (help·info)

In music, the subtonic is the lowered seventh degree of the scale, as opposed to the leading tone (vii). For example, in the A major scale (white keys on a piano, starting on A), the subtonic is the note G (in C major this would be B♭); and the subtonic chord uses the notes G, B, and D (in C: B♭-D-F). In music theory, the subtonic chord is symbolized with the Roman numeral ♭VII for a major triad built on the note, or ♭vii for a minor triad; in a minor key, the flat symbol is sometimes omitted by some theorists because the subtonic note appears in the natural minor scale, but the flat symbol is usually used for the major scale because the subtonic is a non scale note.

In classical music, use of the subtonic is generally rare in major keys apart from reference to the subdominant key (one less sharp or one more flat), but the subtonic chord is considered diatonic in a minor key. However, even in a minor key, use of the subtonic, while implied in some pre-Baroque music due to the use of "minor-sounding" musical modes, was never popular in much of traditional classical music, apart from references to the relative major key, since the subtonic is the dominant of the relative major. Meanwhile, in pop and rock music the subtonic is rather common. Also, in Jazz music the subtonic is used very often as dominant 7th type chord often leading back to the tonic or to the sub.

Minor key non-classical music has seen most of the use of the subtonic. It often functions as an alternate to a minor dominant chord, and is often led into and out of the tonic chord.

"Subtonic" also refers to a relationship of musical keys. For example, relative to the key of C major, the key of B♭ major is the subtonic. Modulation to the subtonic is relatively rare, compared with, say, modulation into the dominant.

Note "sub" chords found in the Minor Scale Harmony:

Tonic = i

Supertonic = ii or iiº

Mediant = ♭III or ♭III+

Subdominant = iv or IV

Dominant = V or v

Submediant = ♭VI

Raised submediant = viº

Subtonic = ♭VII

Leading tone = viiº