Consonance

Consonance is a perceptual quality of sound in which two or more tones sounded together are judged to be harmonically pleasant, stable, or resolved. It is typically contrasted with dissonance, which is heard as tense, unstable, or requiring resolution. Perception of consonance is influenced by context, timbre, and cultural background, and is not an absolute property of a sound.

Acoustically, consonance is often linked to the harmonic series and simple frequency ratios. Intervals with simple ratios such as the octave (2:1), the perfect fifth (3:2), and the unison (1:1) tend to align harmonics more closely and produce smoother, less beating sound. The fourth (4:3) is sometimes treated as consonant within certain harmonic contexts, though its status can vary by style and period. More complex ratios, and intervals with rapid beating between partials, are typically heard as less consonant or more dissonant. Instrumental timbre also affects the perception of consonance, since the presence of multiple overlapping overtones can reinforce or diminish the sense of stability.

In Western tonal music, consonance forms a hierarchy with perfect consonances (unison, octave, perfect fifth) at the top and imperfect consonances (major and minor third, major and minor sixth) considered stable but less so than the perfect intervals. Dissonant chords and intervals create tension that leads to resolution to consonant sonorities. Other musical cultures and tuning systems can shift these judgments, illustrating that consonance is both a physical phenomenon and a culturally informed perception.