Modal scales are found in various forms. Plainchant, the traditional music of the Catholic liturgy, makes use of eight modes, the church modes, with names derived from very different, earlier Greek modes. The first church mode is the Dorian, the third the Phrygian, the fifth the Lydian and the seventh the Mixolydian. These are the so-called authentic modes, their range from D to D, E to E, F to F and G to G respectively. Each authentic mode has an associated plagal mode using the same final note, but within an octave range that starts a fourth below the final and extends a fifth above it. These plagal modes take the Greek prefix hypo-, as in Hypodorian, Hypophrygian, Hypolydian and Hypomixolydian. Theorists later distinguished two further pairs of authentic and plagal modes, the Aeolian, A to A, and the Ionian, C to C. The Locrian mode, B to B, is inaccurately named, but was early distinguished as Hyperaeolian. Early polyphony, reaching a height of perfection in the 16th century, is modal, and its techniques continue to be studied as modal counterpoint, a necessary element in the training of a musician. These listed modes and a variety of other modes may be distinguished in folk-music, while composers of the 20th century have constructed their own synthetic scales or modes.