Origins
The word 'consonance' entered English around 1432 from Old French 'consonance,' derived from Latin 'consonantia,' meaning 'agreement' or 'harmony of sounds.' The Latin word is built from the present participle of 'consonāre' — to sound together — combining the prefix 'con-' (together, with) and 'sonāre' (to sound). At its root, consonance is the experience of sounds that agree, that blend, that seem to belong together.
The concept predates the word by many centuries. The Pythagorean school of ancient Greece, active from the sixth century BCE, discovered that the most pleasing musical intervals correspond to simple mathematical ratios between string lengths. The octave (2:1), the perfect fifth (3:2), and the perfect fourth (4:3) were deemed consonant because their frequency ratios are simple whole numbers, producing sound waves that align regularly. More complex ratios — like the major second (9:8) or the tritone (45:32) — produce waves that clash, creating the restless, tense quality called dissonance.
This Pythagorean framework shaped Western music theory for over two millennia. The Latin terminology of 'consonantia' and 'dissonantia' formalized the distinction, and it passed into every European language. What changed over the centuries was not the terminology but the classification: intervals once deemed intolerably dissonant (the major third, for example) were gradually accepted as consonant, expanding the harmonic vocabulary available to composers. What sounded like discord to a medieval monk sounded like sweetness to a Renaissance choirmaster.
Later History
The relationship between consonance and dissonance has been one of the central questions of Western music aesthetics. In medieval and Renaissance theory, the distinction was treated as quasi-moral: consonance was good, dissonance was deviation requiring correction. In the common-practice period (roughly 1600–1900), dissonance was permitted as a source of tension that must resolve to consonance — the entire harmonic language of Bach, Mozart, and Beethoven rests on this principle of tension and resolution. In the twentieth century, composers like Schoenberg, Webern, and Varèse challenged the distinction itself, arguing that all sound combinations are equally valid and that the consonance-dissonance hierarchy is a cultural construction rather than a natural law.
The metaphorical use of 'consonance' — to describe ideas, values, or actions that agree — preserves the original Latin meaning with remarkable fidelity. When we say that someone's actions are 'in consonance with' their stated values, we are using a sound metaphor: their deeds and words 'sound together' without clashing. The persistence of this metaphor across centuries testifies to the deep human intuition that harmony among sounds and harmony among ideas are, at some fundamental level, the same kind of experience.