definition v1 of leading-tone

The leading tone is scale degree 7 of a major key — the pitch a semitone below the tonic — and the bearer of the leading function: the point of strongest upward pull, whose half-step resolution to the tonic is the sharpest edge of cadential motion and the voice-leading engine that completes the dominant's pull home. Parameters: (1) intervallic status — in a major key the seventh scale degree sits a semitone (diatonic semitone) below the tonic (in C major, B), and it is this half-step distance that gives it its leading character; the corresponding degree in a natural minor key is a subtonic, a whole tone below the tonic, and does not bear the leading function; (2) functional role — the leading tone is the degree that resolves upward by semitone to the tonic; it appears in the dominant chord as its third (B in a G major triad over C) and supplies the voice-leading urgency that makes the dominant–tonic cadence close; (3) relational definition — the leading tone is defined relative to the tonic (the leading tone of C major is B), and its function is the completion of the dominant's resolution, so it is the dominant's pull expressed at the voice-leading level. Persistence mechanism: codified in Western tonal and voice-leading theory, taught in harmony and counterpoint curricula (scale-degree analysis; the leading-tone–tonic resolution as a basic voice-leading pattern), reproduced in composition and analysis practice (cadence analysis, the leading tone's semitone pull in the final cadence of a phrase), and maintained through the conventions of tonal notation (the raised seventh in minor keys, the harmonic minor, exists to produce the leading tone). It is distinguished from the subtonic (the natural-minor seventh degree, a whole tone below the tonic — same scale position, no half-step, no leading function), from the dominant (the chord/degree to which the leading tone belongs and which it sharpens — the leading tone is the third of the dominant chord, its semitone voice, not the fifth-degree function itself), and from a bare pitch (any point on the pitch axis; the leading tone is a pitch bearing the specific function of the semitone pull to the tonic). [formal: dominantis | substrate: mind | horizon: centuries | explicit: yes | epoch: 0.01]