Function (music)

cIn music diatonic functionality is the assumption used in tonal music theory that a pitch or pitch class and its enharmonic equivalents can not be used in the same way. For example a C# cannot be used as a Db, however this is not to say that they are not enharmonic equivalents, for they are in equal temperament, but rather that a Bb minor chord does not have a C# as its third, but a Db, and an F# major scale does not have a Db as its fifth degree, but a C#.

Thus a pitch may or may not fulfill one or more functions. Functional tonality refers to tonality which uses diatonic functions, non-functional tonality being when the diatonic elements are present (for instance the major scale) but do not use or fulfill their possible function as in, for instance, pandiatonicism.

In theory as commonly taught in the US, there are seven different functions, while in Germany, from the theories of Hugo Riemann, there are only three, and functions besides the tonic, subdominant and dominant are named as "parallels" (US: relatives) to those functions. For instance in C major an a minor is the Tonic parallel or Tp.

In the United States, Germany, and other places the diatonic functions are:

Function	Roman Numeral	German	German abbreviation
Tonic	I	Tonic	T
Supertonic	II	Subdominant parallel	Sp
Mediant	III	Dominant parallel	Dp
Sub-Dominant	IV	Subdominant	S
Dominant	V	Dominant	D
Sub-Mediant	VI	Tonic parallel	Tp
Leading/Subtonic	VII	incomplete Dominant seventh	[slashed-D] Ð7

See: Function, chord progression.