“De preceptis artis musicae” was the theoretical treatise compiled by Guillelmus in the past due 15th century. It had been not arranged well repeating ideas and totally omitting others which were implied by the task. The discourse is certainly important for the reason that it provides instructions in the utilization and execution of gymel and fauxbourdon. The word gymel was utilized by the British in their explanation of an individual voice put into two elements of similar range. Hence if one component entends from A to D the next part could range between C to F. Likewise the fauxbourdon, though designed being a short-cut in sight-singing, supplied for the contratenor or supranus to sing another above or below the cantus firmus or the cantus firmus an octave above the real cantus firmus. The effect is some sixths or thirds and triads constructed in the first inversion. In the treatise by Guillelmus the design was constant except in the initial and last chord or the start and cadence. When he utilized the word “fauxbourdon” he was the first ever to mean a method for extemporaneous polyphony constructed upon an currently existing cantus firmus.