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In music, consonance and dissonance form a structural dichotomy in which the terms define each other by mutual exclusion: a consonance is what is not dissonant, and reciprocally. However, a finer consideration shows that the distinction forms a gradation, from the most consonant to the most dissonant. Consonance and dissonance define a level of sweetness / harshness, pleasantness / unpleasantness, acceptability / unacceptability, of the sounds or intervals under consideration. As Hindemith stressed, "The two concepts have never been completely explained, and for a thousand years the definitions have varied" . The opposition 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-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 consonant in the context of acoustics (e.g. a major triad in atonal music). 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 is heard. For this reason, consonance and dissonance have been considered particularly in the case of polyphonic Occidental 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, Noise music and Noise (acoustic).) While consonance and dissonance exist only between sounds and therefore necessarily describe intervals (or chords), Occidental music theory often considers that, in a dissonant chord, one of the tones alone is in itself the dissonance: it is this tone in particular that needs "resolution" through a specific voice leading. ==Consonance== The definition of consonance has been variously based on experience, frequency, and both physical and psychological considerations . These include: *Perception * *Blend/fusion: perception of unity or tonal fusion between two notes (Stumpf; ) *Frequency ratios: with ratios of lower simple numbers being more consonant than those that are higher (Pythagoras). Many of these definitions do not require ''exact'' integer tunings, only approximation. * *''Coincidence of partials'': with consonance being a greater coincidence of partials (called harmonics or overtones when occurring in harmonic timbres) (, ). 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 the entry under 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 . Although Helmholtz's work focused almost exclusively on harmonic timbres and also the tunings, subsequent work has generalized his findings to embrace non-harmonic tunings and timbres (; , ; , ; , ; , ). * *''Fusion or pattern matching'': fundamentals may be perceived through pattern matching of the separately analyzed partials to a best-fit exact-harmonic template (, ) or the best-fit subharmonic (). Harmonics may be perceptually fused into one entity—consonances being those that include: * * *Perfect consonances: * * * *unisons and octaves * * * *perfect fourths and perfect fifths * * *Imperfect consonances: * * * *major thirds and minor sixths * * * *minor thirds and major sixths *Both * *Continuity: consonances are continuous and dissonances are intermittent in sensation, determined by coincidence of partials (, ). These may be generalized as ''simplicity''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Consonance and dissonance」の詳細全文を読む スポンサード リンク
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