The leading tone — what one semitone does to an entire harmony

One semitone that pulls

Play a C major scale upward and stop on the B. The note does not stand still; it wants to continue. That restlessness is not a feeling you have to bring with you — it appears in people who have never had a music lesson. The seventh note of a major scale is therefore called the leading tone: it leads to the tonic.

The reason lies in the distance. Between all other adjacent degrees of a major scale there is a whole tone — except between the third and fourth and between the seventh and eighth. There it is a semitone, the smallest possible step in the system. And the closer two notes lie, the more strongly the lower one pulls towards the upper.

These two semitone steps are not equally strong. The one between the third and fourth degrees barely registers. The one between the seventh and the octave carries the entire cadence, because it aims at the most important note of the key. Remove it — lower the seventh degree to a whole tone — and the sense of direction disappears at once; the scale sounds old, modal, like folk song. That is precisely Mixolydian.

Why the dominant seventh sounds so decided

The leading tone does its work not alone but inside a chord. The fifth degree of C major is G major: G–B–D. The B within it is the leading tone. Add the minor seventh — the F — and you have G7, a chord containing two notes that press in opposite directions at once.

The B wants to go up a semitone to C. The F wants to go down a semitone to E. Between B and F lies a tritone, the least stable interval in the system. Resolve both simultaneously and you land on C and E — two of the three notes of the C major triad. The chord therefore resolves not arbitrarily, but because two semitone pulls aim at the same target.

That is why the cadence G7–C is so inescapable that it closes practically every piece of Western music between 1650 and 1900. And that is why the trick of ending a piece on the dominant works when you want to keep tension open: the ear goes on waiting for a resolution that never comes.

Minor has to borrow its leading tone

The natural minor scale has no leading tone. In A minor the notes are A–B–C–D–E–F–G–A; between G and A lies a whole tone. The dominant would therefore be E–G–B, a minor triad, and that does not pull. So since the Baroque, composers artificially raise the seventh degree in minor: G becomes G♯, and E minor becomes E major.

This scale is called harmonic minor, and it has a side effect. Between the sixth degree and the newly raised seventh — F and G♯ — a gap of a tone and a half opens up, an augmented second. That step is characteristic, awkward and hard to sing; it gives harmonic minor its faintly oriental flavour.

Because that disrupts a melodic line, there is a third variant: melodic minor. Ascending, the sixth and seventh degrees are both raised so the melody runs smoothly to the tonic; descending, where no leading tone is needed, it reverts to the natural form. This odd asymmetry is not a theorist’s quirk but the direct consequence of a single requirement: to have a semitone at the top and not at the bottom.

Bach’s music is full of it. The Minuet in G minor from the Notebook for Anna Magdalena Bach carries an F♯ again and again although the key signature has two flats — that is the borrowed leading tone, and it is why every phrase there arrives where it should.

From practice

The exercise that makes the leading tone tangible fastest needs only a voice: Sing a major scale upward and stop on the seventh degree. Nearly every group sings the final note by itself, unprompted. Anyone who has observed that in themselves needs no definition afterwards.

At the instrument comes the second exercise: the same cadence in three versions. First G–C, then G7–C, then G minor–C. Each time the question is which version closes most decisively. The answer is as clear among beginners as among advanced players — and at the third example everybody pauses, because without a leading tone the sense of closure simply vanishes.

In choral work the leading tone is a practical intonation topic. Singers tend to take it too low, because a semitone is narrow and the voice shortens the distance. The usual instruction is therefore to sing the leading tone deliberately high, almost over the top. In just intonation it does in fact sit higher than on the piano — choral practice is acoustically in the right here, against the keyboard.

A typical error when writing your own settings: taking the leading tone downward. Write a B in G7 and move to A in the next chord and you hear immediately that something is wrong, without knowing the rule. The leading tone goes up — that is not a convention but the only direction in which it pulls.

Music without a leading tone: the church modes

Before roughly 1600 the leading tone was not a given. The church modes differ precisely in where their semitones fall. Mixolydian corresponds to a major scale with a lowered seventh degree — in G, an F instead of F♯. The cadence there no longer aims; it arrives without being pulled. Almost everyone knows the sound from folk and rock, where the progression G–F–C is typical.

Dorian is minor with a raised sixth degree and likewise has no leading tone. The English folk song “Scarborough Fair” is Dorian, and its peculiarly suspended, not exactly sorrowful character comes from exactly that: the mode has neither the drive of major nor the darkness of natural minor.

Historically, introducing a leading tone into modal settings was a practice known as musica ficta: singers raised the seventh degree at cadences although it was not written, because otherwise the ending felt open. The leading tone was therefore a performance habit first and became theory only afterwards — an observation of the ear that hardened into a rule.