This mass on a plainchant cantus firmus for the feast of the Assumption is thought to have been the exercise or test-piece submitted by Fayrfax to support his application for the Oxford degree of MusD granted to him in June 1511. It displays considerable learning in its exploration of subtleties of notation and of numerically powerful musical construction based on interlocking symmetries and proportions, but these recondite properties are largely inaudible and indeed invisible in the simplified notation of all the surviving sources. Those who find the work even more lofty in style than most of Fayrfax’s music may be unduly influenced by knowledge of its background. For five voices: SATBarB. 2025. xvi + 68 pages.