Hypolydian

What it means

Hypolydian is the plagal form of the Lydian mode. Plagal means that the tonal space does not lie predominantly above the finalis but extends substantially below it. Finalis and pool of notes remain the same as in the Lydian mode; different are the ambitus and the reciting tone around which the melody circles.

Musical use

The system of the eight church modes rests on this doubling: to every authentic mode belongs a plagal one with the same finalis. Dorian and Hypodorian, Phrygian and Hypophrygian, Lydian and Hypolydian, Mixolydian and Hypomixolydian each form a pair. The distinction is not theoretical ornament but practically founded: it says in which register a melody moves and where its points of emphasis lie — both important for performance and for assigning the fitting psalm formula.

The Lydian peculiarity, the raised fourth degree above the finalis, is preserved in the plagal form. In practice, however, this note was often lowered, whereby the mode comes close to later major; the sources are inconsistent in this, and editors mark corresponding interventions.

The plagal mode is to be distinguished from the authentic not by the pool of notes but solely by ambitus and reciting tone — whoever looks only at the accidentals cannot tell the two apart.

Hypolydian is in the medieval order the sixth church tone. The finalis is F as with authentic Lydian, but the tonal space runs from C to C. The reciting tone lies on A, a third above the finalis. Many chorales in this mode use B♭ instead of B natural, whereby they sound like modern F major. This shows how closely the later major keys are related to the Lydian modes.

Performance practice

With modal music, first determine finalis and ambitus; only both together tell which mode is present. Watch where the melody has its point of emphasis, and phrase from there. And check in editions the small accidentals above the staff — with Lydian modes this regularly concerns the fourth degree.