Leading-tone

According to Ernst Kurth (1913) the major and minor thirds contain "latent" tendencies towards the perfect fourth and whole-tone, respectively, and thus establishe tonality. However, Carl Dahlhaus (1990) shows that this drive is in fact created through or with harmonic function, a root progression in another voice by a whole-tone or fifth, or melodically (monophonically) by the context of the scale. For example, the leading tone of alternating C chord and F minor chords is either the note E leading to F, if f is tonic, or Ab leading to G, if C is tonic. In the 14th and 15th centuries, the leading-tone is created by the progression from imperfect to perfect consonances, such as a major third to a perfect fifth or minor third to a unison. The same pitch outside of the imperfect consonance is not a leading tone.

As a diatonic function the leading-tone is the seventh scale degree of any diatonic scale when the distance between it and the tonic is a single semitone. In diatonic scales where there is a whole tone between the seventh scale degree and the tonic, such as the Mixolydian mode, the degree is the subtonic.