Equivalence class (music)

This article is about equivalency in music; for equivalency in mathematics see Equality (mathematics) and equivalence class.

In music theory, equivalence class is an equality (=) or equivalence between sets or twelve-tone rows. A relation rather than an operation, it may be contrasted with derivation. "It is not surprising that music theorists have different concepts of equivalence [from each other]..." "Indeed, an informal notion of equivalence has always been part of music theory and analysis. Pitch class set theory, however, has adhered to formal definitions of equivalence."