B as the Leading Tone

B is the seventh degree of the C major scale, called Ti (or Si in some traditions) in movable-doh solfège, and functions in tonal harmony as the leading tone, the pitch sitting a single semitone below the tonic whose strong pull toward resolution upward into the octave is one of the basic engines driving harmonic motion in Western tonal music. This half-step relationship between the seventh degree and the octave is a defining structural feature of the major scale itself, distinguishing it from scales built with a whole step in that position.

B major and B minor sit at a considerable distance from C major on the circle of fifths, the theoretical device mapping key relationships by ascending fifths, which is one reason modulations between C and B feel comparatively dramatic in tonal composition; the same acoustic fact, that resolving a leading tone upward by a single semitone produces a strong sense of arrival, is exploited constantly across genres from classical cadences to popular music's use of a raised seventh to signal an imminent return to the tonic chord.