Consonance and dissonance

In music, consonance and dissonance are categorizations of simultaneous or successive sounds. Within the Western tradition, some listeners associate consonance with sweetness, pleasantness, and acceptability, and dissonance with harshness, unpleasantness, or unacceptability, although there is broad acknowledgement that this depends also on familiarity and musical expertise. The terms form a structural dichotomy in which they define each other by mutual exclusion: a consonance is what is not dissonant, and a dissonance is what is not consonant. However, a finer consideration shows that the distinction forms a gradation, from the most consonant to the most dissonant. In casual discourse, as German composer and music theorist Paul Hindemith stressed,

Perfect octave, a consonant interval

Minor second, a dissonance

"The two concepts have never been completely explained, and for a thousand years the definitions have varied".

The term sonance has been proposed to encompass or refer indistinctly to the terms consonance and dissonance.

Definitions

The opposition between consonance and dissonance can be made in different contexts:

In acoustics or psychophysiology, the distinction may be objective. In modern times, it usually is based on the perception of harmonic partials of the sounds considered, to such an extent that the distinction really holds only in the case of harmonic sounds (i.e. sounds with harmonic partials).
In music, even if the opposition often is founded on the preceding, objective distinction, it more often is subjective, conventional, cultural, and style – or period – dependent. Dissonance can then be defined as a combination of sounds that does not belong to the style under consideration; in recent music, what is considered stylistically dissonant may even correspond to what is said to be consonant in the context of acoustics (e.g. a major triad in 20th century atonal music). A major second (e.g. the notes C and D played simultaneously) would be considered dissonant if it occurred in a J.S. Bach prelude from the 1700s; however, the same interval may sound consonant in the context of a Claude Debussy piece from the early 1900s or an atonal contemporary piece.

In both cases, the distinction mainly concerns simultaneous sounds; if successive sounds are considered, their consonance or dissonance depends on the memorial retention of the first sound while the second sound (or pitch) is heard. For this reason, consonance and dissonance have been considered particularly in the case of Western polyphonic music, and the present article is concerned mainly with this case. Most historical definitions of consonance and dissonance since about the 16th century have stressed their pleasant / unpleasant, or agreeable / disagreeable character. This may be justifiable in a psychophysiological context, but much less in a musical context properly speaking: Dissonances often play a decisive role in making music pleasant, even in a generally consonant context – which is one of the reasons why the musical definition of consonance/dissonance cannot match the psychophysiologic definition. In addition, the oppositions pleasant/unpleasant or agreeable/disagreeable evidence a confusion between the concepts of "dissonance" and of "noise". (See also Noise in music and Noise music.)

While consonance and dissonance exist only between sounds and therefore necessarily describe intervals (or chords), such as the perfect intervals, which are often viewed as consonant (e.g., the unison and octave). Occidental music theory often considers that, in a dissonant chord, one of the tones alone is in itself deemed to be the dissonance: It is this tone in particular that needs "resolution" through a specific voice leading procedure. For example, in the key of C Major, if F is produced as part of the dominant seventh chord (G⁷, which consists of the pitches G, B, D and F), it is deemed to be "dissonant" and it normally resolves to E during a cadence, with the G⁷ chord changing to a C Major chord.

Acoustics and psychoacoustics

Scientific definitions have been variously based on experience, frequency, and both physical and psychological considerations. These include:

Numerical ratios: In classical antiquity, these mainly concerned string-length ratios. From the early 17th century onwards, the ratios were more often expressed as the equivalent ratios of frequencies. Consonance often is associated with the simplicity of the ratio, i.e. with ratios of lower simple numbers. Many of these definitions do not require exact integer tunings, only approximation.^[vague]^{[citation needed]}

Fusion: Perception of unity or tonal fusion between different tones and / or their partials.

Coincidence of partials: With consonance being a greater coincidence of partials.^[9] By this definition, consonance is dependent not only on the width of the interval between two notes (i.e., the musical tuning), but also on the combined spectral distribution and thus sound quality (i.e., the timbre) of the notes (see Critical band). Thus, a note and the note one octave higher are highly consonant because the partials of the higher note are also partials of the lower note.

Dynamic tonality
This section contains promotional content. Please help improve it by removing promotional language and inappropriate external links, and by adding encyclopedic text written from a neutral point of view. (March 2025) (Learn how and when to remove this message): Dynamic tonality^[buzzword] considers consonance to arise from the alignment of harmonic, inharmonic, or dynamic partials of note timbres. "Dynamic tonality" explicitly generalizes the relationship between the harmonic series and just intonation to pseudo-harmonic timbres in corresponding pseudo-just tunings.^[12]^{[page needed]}^{[page needed]}^{[page needed]} In this way, any musical interval can be made consonant or dissonant by aligning the timbre's partials with the interval's tuning.

Music theory

A stable tone combination is a consonance; consonances are points of arrival, rest, and resolution.

— Roger Kamien

An unstable tone combination is a dissonance; its tension demands an onward motion to a stable chord. Thus dissonant chords are "active"; traditionally they have been considered harsh and have expressed pain, grief, and conflict.

— Roger Kamien

Consonances may include:

Perfect consonances:
- unisons and octaves
- perfect fourths and perfect fifths
Imperfect consonances:
- major thirds and minor sixths
- minor thirds and major sixths

Dissonances may include:

Dissonance
- major seconds and minor seventh
- tritones
- minor seconds and major sevenths

Physiological basis

Consonance may be explained as caused by a larger number of aligning harmonics (blue) between two notes. Dissonance is caused by the beating between close but non-aligned harmonics.

Dissonance may be the difficulty in determining the relationship between two frequencies, determined by their relative wavelengths. Consonant intervals (low whole number ratios) take less, while dissonant intervals take more time to be determined.

One component of dissonance – the uncertainty or confusion as to the virtual pitch evoked by an interval or chord, or the difficulty of fitting its pitches to a harmonic series (discussed by Goldstein and Terhardt, see main text) – is modelled by harmonic entropy theory. Dips in this graph show consonant intervals such as 4:5 and 2:3 . Other components not modeled by this theory include critical band roughness, and tonal context (e.g., an augmented second is more dissonant than a minor third although in equal temperament the interval, 300 cents, is the same for both).

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