Consonance and dissonance are terms, used with varying degrees of precision and meaning, that describe the relative stability or instability, pleasantness or unpleasantness, sweetness or harshness, of a chord or interval. As the qualitative nature of this language suggests, perceptions of consonance and dissonance are highly contingent upon factors such as listening culture, musical style, and historical period. For example, some chords considered consonant or stable in Jazz would be considered dissonant and unstable in eighteenth-century music.

Notwithstanding these shifting notions, musical thinkers—from Greek philosophers to American academics—have attempted to categorize and rationalize our basic musical intuition that some things sound more stable or pleasing than others.

The terms consonance and dissonance do not commonly appear in judicial opinions dealing with music copyright infringement claims. The opinion in Swirsky v. Carey (2004) mentions the importance of consonance and dissonance as seasoning elements of a work, and part of a larger work of musical expression. Not surprisingly, the court in Tempo Music v. Famous Music (1993) a case dealing with the question of the eligibility of jazz harmonies as copyrightable expression, also touches upon the terms consonance and dissonance.

References to other Glossary terms: