Leaving Home and Coming Back

Sing the first six notes of a scale and stop. Most people find it faintly unpleasant, and want to finish.

That wanting is the whole of tonal music. One note has been established as home, everything else is heard in relation to it, and the distance from home is a force the listener feels without any training whatsoever.

What makes a note the tonic is not any property of the frequency. It is behaviour: the music returns to it, cadences arrive on it, the notes around it lean towards it. Transpose the piece and a different frequency does the same job. Home is a role, and the interesting consequence is that a piece can quietly transfer the role to a new note while it is going on.

The local unit is the cadence (the harmonic formula that closes a phrase) and its varieties are effectively punctuation. A perfect cadence is a full stop: the dominant falls to the tonic and the phrase is closed. An imperfect cadence ends on the dominant, which is a comma: the sense is incomplete and something must follow.

The one worth knowing is the interrupted cadence. The music sets up the full stop, everything points at the tonic, and it delivers something else, usually the relative minor. The phrase cannot end, so it must continue. It is the harmonic equivalent of a sentence that runs on past where you expected the period, and it depends entirely on the listener having internalised the expectation, which nearly every listener in a Western musical culture has, without instruction.

That expectation is strong enough to produce physical discomfort, which is why film and advertising exploit it constantly. A cue that builds towards a cadence and cuts one chord short leaves the listener holding an unresolved expectation, and that unresolved feeling attaches to whatever is on screen. The effect works best when nobody notices the mechanism.

At the larger scale, the equivalent device is modulation: moving the sense of home to a new key.

This is how long pieces are built. A movement establishes a key, travels to another, spends time somewhere unstable and eventually comes back, and the return is an event because the absence was long. A listener who follows none of the technical detail still feels the arrival, because arriving after a long absence is perceptible without a vocabulary.

Which is also why a great deal of music does not work this way and is none the worse.

Modal music (plainchant, most folk traditions, a large part of rock, and much of what film composers reach for when they want atmosphere) establishes a home note without the strong pull of functional harmony. There is no dominant demanding resolution. The music can circle indefinitely, sustaining a mood rather than pressing towards a goal.

That difference explains something a listener notices immediately: a modal riff can hold an eight-minute track together, while an eight-bar classical phrase already sounds as though it needs to end. Different machinery, different natural durations. Neither is more sophisticated; they answer different questions about what music is for.

One final note on the chord progression everyone notices. The same four chords underlie an implausible number of songs, and people take this as evidence of laziness.

A progression is a shape of tension and release, and its meaning comes from that shape. What differs between songs built on it is everything else: melody, rhythm, timbre, words, the way the sections are proportioned. This is also why musical copyright is such a mess in the courts: the features that make two songs feel similar are frequently the ones that belong to everyone, and the features that are genuinely original are hard to describe to a jury.