Consonance is a combination of pitches that merge into a blended, balanced whole. Perfect consonances include the unison, octave, and fifth; imperfect ones, the thirds and sixths. Physically, consonance is linked to simple frequency ratios (the octave 2:1, the fifth 3:2).
Consonance and dissonance are the two poles between which all harmony lives. Consonance gives a sense of repose, completion, of a “home” to which the musical thought returns; a work usually ends on a consonant triad. Yet the notion of consonance has changed through history: what the medieval ear heard as tension (the third) is for us a mild consonance. Without the alternation of tension and repose, dissonance and consonance, music would lose its motion and its breath.
