In music theory, a leading tone (also called subsemitone or leading note in the UK) is a note or pitch which resolves or "leads" to a note one semitone higher or lower, being a lower and upper leading tone, respectively. Typically, the leading tone refers to the seventh scale degree of a major scale (), a major seventh above the tonic. In the movable do solfège system, the leading tone is sung as si.
A leading-tone triad is a triad built on the seventh scale degree in a major key (viio in Roman numeral analysis), while a leading-tone seventh chord is a seventh chord built on the seventh scale degree (viiø7). Walter Piston considers and notates viio as V0
7, an incomplete dominant seventh chord. (For the Roman numeral notation of these chords, see Roman numeral analysis.)
Leading-tone triad
A leading-tone chord is a triad built on the seventh scale degree in major and the raised seventh-scale-degree in minor. The quality of the leading-tone triad is diminished in both major and minor keys. For example, in both C major and C minor, it is a B diminished triad (though it is usually written in first inversion, as described below).
According to John Bunyan Herbert, (who uses the term "subtonic", which later came to usually refer to a seventh scale degree pitched a whole tone below the tonic note),
The subtonic [leading-tone] chord is founded upon seven (the leading tone) of the major key, and is a diminished chord... The subtonic chord is very much neglected by many composers, and possibly a little overworked by others. Its occasional use gives character and dignity to a composition. On the whole, the chord has a poor reputation. Its history, in brief, seems to be: Much abused and little used.
Function
The leading-tone triad is used in several functions. It is commonly used as a passing chord between a root position tonic triad and a first inversion tonic triad: that is, "In addition to its basic function of passing between I and I6, VII6 has another important function: it can form a neighboring chord to I or I6." In that instance, the leading-tone triad prolongs tonic through neighbor and passing motion. The example below shows two measures from the fourth movement of Beethoven's Piano Sonata No. 3 in C major, Op. 2 in which a leading-tone triad functions as a passing chord between I and I6.
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The leading-tone triad may also be regarded as an incomplete dominant seventh chord: "A chord is called 'Incomplete' when its root is omitted. This omission occurs, occasionally, in the chord of the dom.-seventh, and the result is a triad upon the leading tone."
Some sources say the chord is not a chord; some argue it is an incomplete dominant seventh chord, especially when the diminished triad is written in its first inversion (resembling a second inversion dominant seventh without a root):
The subtonic [i.e. leading-tone] chord is a very common chord and a useful one. The triad differs in formation from the preceding six [major and minor diatonic] triads. It is dissonant and active... a diminished triad. The subtonic chord belongs to the dominant family. The factors of the triad are the same tones as the three upper factors of the dominant seventh chord and progress in the same manner. These facts have led many theorists to call this triad a 'dominant seventh chord without root.'... The subtonic chord in both modes has suffered much criticism from theorists although it has been and is being used by masters. It is criticized as being 'overworked', and that much can be accomplished with it with a minimum of technique.
For example, viio6 often substitutes for V4
3, which it closely resembles, and its use may be required in situations by voice leading: "In a strict four-voice texture, if the bass is doubled by the soprano, the VII6 [viio6] is required as a substitute for the V4
3".
Voice leading
Since the leading-tone triad is a diminished triad, it is usually found in its first inversion: According to Carl Edward Gardner, "The first inversion of the triad is considered, by many, preferable to root position. The second inversion of the triad is unusual. Some theorists forbid its use."
In a four-part chorale texture, the third of the leading-tone triad is doubled in order to avoid adding emphasis on the tritone created by the root and the fifth. Unlike a dominant chord where the leading tone can be frustrated and not resolve to the tonic if it is in an inner voice, the leading tone in a leading-tone triad must resolve to the tonic. Commonly, the fifth of the triad resolves down since it is phenomenologically similar to the seventh in a dominant seventh chord. All in all, the tritone resolves inward if it is written as a diminished fifth (m. 1 below) and outward if it is written as an augmented fourth (m. 2).
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Leading-tone seventh chord
The leading-tone seventh chords are viiø7 and viio7, the half-diminished and diminished seventh chords on the seventh scale degree () of the major and harmonic minor. For example, in C major and C minor, the leading-tone seventh chords are B half-diminished (B–D–F–A) and B diminished (B–D–F–A♭), respectively.
Leading-tone seventh chords were not characteristic of Renaissance music but are typical of the Baroque and Classical period. They are used more freely in Romantic music but began to be used less in classical music as conventions of tonality broke down. They are integral to ragtime and contemporary popular and jazz music genres.
Composers throughout the common practice period often employed modal mixture when using the leading-tone seventh chord in a major key, allowing for the substitution of the half-diminished seventh chord with the fully diminished seventh chord (by lowering its seventh). This mixture is commonly used when the leading-tone seventh chord is functioning as a secondary leading-tone chord.
The example below shows fully diminished seventh chords in the key of D major in the right hand in the third movement of Mozart's Piano Sonata No. 5 in G major.
![\new PianoStaff <<
\new Staff <<
\relative c' {
\clef treble \key g \major \time 3/8
\set Score.currentBarNumber = #64
\bar ""
<e e'>8 e'16[ dis fis e]
\once \override DynamicLineSpanner.staff-padding = #3.5 g16([\p e cis bes)] \once \override DynamicLineSpanner.staff-padding = #3.5 a8\f
g'16([ e cis bes)] \once \override DynamicLineSpanner.staff-padding = #3.5 a8\f
g'16([ e cis bes)] \once \override DynamicLineSpanner.staff-padding = #3.5 a8\f
g'16([ e cis bes)] \once \override DynamicLineSpanner.staff-padding = #3.5 a8\f
r r <d fis a>\f
}
>>
\new Staff <<
\new Voice \relative c' {
\clef bass \key g \major \time 3/8
R4.
r8 r \clef treble <cis e g>
r8 r <cis e g>
r8 r <cis e g>
r8 r <cis e g>
\clef bass \once \override DynamicLineSpanner.staff-padding = #3.5 d,16([^\p fis a d)] fis8
}
>>
>>](https://upload.wikimedia.org/score/c/x/cx5ys1mac15a1f1qrr7sjbdqtzfqwpq/cx5ys1ma.svg)
Function
The leading-tone seventh chord has a dominant function and may be used in place of V or V 7. Just as viio is sometimes considered an incomplete dominant seventh chord, a leading-tone seventh chord is often considered a "dominant ninth chord without root".)
For variety, leading-tone seventh chords are frequently substituted for dominant chords, with which they have three common tones: "The seventh chord founded upon the subtonic [in major]... is occasionally used. It resolves directly to the tonic... This chord may be employed without preparation."
Voice leading
In contrast to leading-tone triads, leading-tone seventh chords appear in root position. The example below shows leading-tone seventh chords (in root position) functioning as dominants in a reduction of Mozart's Don Giovanni, K. 527, act 1, scene 13.
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François-Joseph Fétis tunes the leading-tone seventh in major 5:6:7:9.