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Some later grammarians applied the terms arsis and thesis to the prosody of words. Pseudo-Priscian (6th or 7th century AD), appears to have been considering not the metre but the pitch of the voice when he wrote: "In the word , when I say "natu", the voice is raised and there is arsis; but when "ra" follows, the voice is lowered and there is thesis. ... The voice itself, which is formed out of words, is assigned to arsis until the accent is completed; what follows the accent is assigned to thesis." Gemistus Pletho, a 14th–15th century Byzantine scholar, seems to adopt this meaning in one passage where he defines arsis as a change from a lower-pitched sound to a higher-pitched one, and thesis the reverse.