Consonance and dissonance

In music, the terms consonance and dissonance describe how simultaneous or successive sounds relate to each other. In the Western tradition, consonance is often linked to sweetness, pleasantness, or acceptability, while dissonance is tied to harshness, unpleasantness, or unacceptability—though listeners’ familiarity with the music and their level of expertise can shift these associations. The two concepts form a binary where each is defined by the absence of the other: a consonance is simply what is not dissonant, and vice versa. Yet a closer look reveals that the distinction is actually a sliding scale, ranging from the most consonant to the most dissonant. As composer and theorist Paul Hindemith noted, the definitions have shifted over a thousand years and have never been fully settled. The term “sonance” has been suggested as a catch-all for both ideas.

Definitions of the opposition vary by context. In acoustics or psychophysiology, the distinction can be objective, typically based on how the harmonic partials of sounds are perceived—but this only holds for sounds that actually have harmonic partials. In music, the opposition often draws on that objective foundation but is more subjective, cultural, and style-dependent. Dissonance in a musical sense can mean a combination that doesn’t fit the style in question; in some recent music, what is acoustically consonant (like a major triad) may be treated as stylistically dissonant. For example, a major second (C and D together) would sound dissonant in a Bach prelude from the 1700s, but the same interval might feel consonant in a Debussy piece from the early 1900s or in atonal contemporary work. The distinction mostly applies to simultaneous sounds; for successive sounds, consonance or dissonance depends on how well the listener retains the memory of the first pitch while hearing the second. Because of this, the concepts have been studied especially in Western polyphonic music, and this article focuses on that tradition. Since about the 16th century, most historical definitions have stressed pleasant/unpleasant or agreeable/disagreeable qualities. This makes sense in a psychophysiological context but less so in a musical one: dissonances often help make music enjoyable, even in a generally consonant setting—which is why the musical definition can’t match the psychophysiological one. Moreover, equating dissonance with unpleasantness confuses it with noise.

Consonance and dissonance only exist between sounds, so they describe intervals or chords—like perfect intervals (unison, octave), which are often viewed as consonant. In Western music theory, a dissonant chord often has one tone that is considered the dissonance itself; that tone requires resolution through a specific voice-leading procedure. For instance, in the key of C major, the F in a G7 chord (G, B, D, F) is deemed dissonant and normally resolves to E during a cadence, turning the G7 into a C major chord.

Scientific definitions have been based on experience, frequency, and physical or psychological factors. One approach uses numerical ratios: in antiquity, these were string-length ratios; from the early 17th century onward, they became frequency ratios. Consonance is often linked to simpler ratios (lower small numbers), though exact integer tunings aren’t required—only approximation. Another approach is fusion, where different tones or their partials are perceived as a single tone. A third approach involves the coincidence of partials: consonance increases when more partials align. This means consonance depends not only on the interval’s width (tuning) but also on the combined spectrum and timbre of the notes. For example, a note and its octave are highly consonant because the higher note’s partials are already partials of the lower note.

In music theory, a stable tone combination is a consonance—a point of arrival, rest, or resolution. An unstable combination is a dissonance, whose tension pushes the music toward a stable chord. Dissonant chords are thus “active” and have traditionally been considered harsh, expressing pain, grief, or conflict. Consonances are divided into perfect (unisons, octaves, perfect fourths and fifths) and imperfect (major thirds and minor sixths, minor thirds and major sixths). Dissonances include major seconds and minor sevenths, tritones, and minor seconds and major sevenths.

Physiologically, when two notes with slightly different frequencies are played together, they produce a beating “wah-wah-wah” sound. This effect is used to create the Voix céleste.