# Complement (music)

In music theory, * complement* refers to either traditional

**interval complementation**, or the

**aggregate complementation**of twelve-tone and serialism.

In interval complementation a complement is the interval which, when added to the original interval, spans an octave in total. For example, a major 3rd is the complement of a minor 6th. The complement of any interval is also known as its *inverse* or *inversion*. Note that the octave and the unison are each other's complements and that the tritone is its own complement (though the latter is "re-spelt" as either an augmented fourth or a diminished fifth, depending on the context).

In the aggregate complementation of twelve-tone music and serialism the complement of one set of notes from the chromatic scale contains all the *other* notes of the scale. For example, A-B-C-D-E-F-G is *complemented* by B♭-C♯-E♭-F♯-A♭.

Note that *musical set theory* broadens the definition of both senses somewhat.