Enharmonic.

A term used in modern theory to denote different ways of ‘spelling’ the name of one note: for example B = C = D, C = D etc. An ‘enharmonic change’ is the respelling of a note in accordance with its changing function, for instance D being renamed C in the modulation from D major to A major in Chopin's Second Scherzo op.31. An ‘enharmonic modulation’ involves the respelling of a key, usually when there is a change in mode, for example from C minor to D major in Chopin's Fantaisie-impromptu op.66. Two notes that sound the same but are spelt differently are said to be ‘enharmonically equivalent’; thus enharmonic equivalents are musical homonyms. In principle, enharmonic relationships can exist only in a system of equal temperament, in which the octave is divided into 12 equal semitones; but even in intonation systems where, say, F and G are not performed at exactly the same pitch, their enharmonic association can nevertheless be perceived by the listener, and exploited by the composer. For a definition of ‘enharmonic’ as applied to ancient Greek music, see Tetrachord.

JULIAN RUSHTON