The idea is ancient — Pythagoras described it in the sixth century BCE — and central to the classical music of India, where melody is built directly on the natural resonances of a drone. Western music largely abandoned pure tuning with the adoption of equal temperament, which divides the octave into twelve mathematically equal semitones, enabling free modulation at the cost of slightly mistuning every interval. Michael Harrison's work reclaims Just Intonation as a compositional foundation, building tuning systems in which the precise proportions between pitches determine not only harmony but structure, duration, and form.