differs. In the plagal modes, the tenor is a third lower than the tenor of the corresponding authentic mode, except in mode 8 (Hypomixolydian), where it is raised to a 4th above the finalis (a second below the tenor of the authentic mode 7) in order to avoid the "unstable" degree ti, which may be flattened (in the authentic mode 3, the tenor is similarly raised to the sixth above the finalis, and the tenor of plagal mode 4--Hypophrygian--is therefore also a fourth above the finalis).

In Byzantine modal theory (octoechos),