He recognizes two kinds of measure—triple or perfect, and duple or imperfect.
Duple (sometimes called even measure, or even time), in which there are two beats, the first one being accented.
The Pavan has been mentioned before, as the dance in Duple time which preceded the Galliard which was in a triple rhythm.
Duple time did not come into general use until the beginning of the fourteenth century.
In many bars it is almost impossible to distinguish whether the tune is triple or duple.