enharmonos

Enharmonos, from the Greek enharmonós meaning "in tune" or "harmonious," is a term used in ancient Greek music theory to designate the enharmonic genus, one of the three genera used to describe the diatonic tetrachord. In this scheme, a tetrachord spanning a perfect fourth is divided into four pitches with two very small intervals in the upper part, formed by microtonal adjustments (limma or diesis) that are smaller than a semitone. The result is a theoretical system that allows a richer microtonal color within the same span, distinguishing it from the diatonic and chromatic genera.

Historically, enharmonos was developed by Greek theorists such as Aristoxenus and further elaborated by later writers like Aristides Quintilianus and Ptolemy in their treatises on tuning and harmony. It remained a theoretical construct rather than a standardized tuning used in everyday performance, complemented by other genera in the Greek tradition. With the shift toward the diatonic and later modal and tonal systems, the enharmonic genus gradually fell from practical use, though it continued to influence medieval and Renaissance interest in microtonality.

In modern usage, the term enharmonos survives mainly in historical and theoretical discussions of Greek music theory. The related adjective enharmonic is more common in describing pitches that are identically pitched but differently named in contemporary Western notation, a concept only loosely connected to the ancient genus.