Diesis (scale theory)

The diesis (precisely the mosdiesis) of a mos scale is the interval that is the difference between two enharmonic notes, i.e. the diminished mosstep or the negative diminished mosstep, whichever is positive. In soft (L:s < 2:1) scales, it is the diminished mosstep. In hard (L:s > 2:1) scales, it is the negative diminished mosstep, since the diminished mosstep itself is negative. In basic (L:s = 2:1) scales, it vanishes.

In particular, the diesis or enharmonic diesis in the diatonic scale is the diminished second or the negative diminished second, whichever is positive. For example, the interval of C#-Db or Db-C#.

If the fifth approximates the just interval 3/2, then the diesis or the negative diesis approximates the Pythagorean comma. In meantone, the diesis also approximates 128/125, the augmented comma, which traditionally goes by the name of diesis.

See also

• Diesis (disambiguation page)