Arsis thesis musica

Aristoxenus appears to be the first writer in whose surviving work the word arsis is used specifically in connection with rhythm. Instead of thesis, he uses the word basis ("step"). However, in other Greek writers from Plato onwards, the word basis referred to the whole foot (i.e. the sequence of arsis and thesis).

In a metrical dactyl (– ⏑⏑), according to Marius Victorinus and other writers on metre, the first syllable was the arsis, and second and third were the thesis; in an anapaest (⏑⏑ –) the arsis was the first two syllables, and the thesis the third.

In music and prosody, arsis and thesis (plural arses and theses) are the stronger and weaker parts of a musical measure or poetic foot. However, because of contradictions in the original definitions, writers use these words in different ways. In music, arsis is an unaccented note ( upbeat ), while the thesis is the downbeat.

Arsis and thesis in music. In measured music, the terms arsis and thesis "are used respectively for unstressed and stressed beats or other equidistant subdivisions of the bar". Thus in music the terms are used in the opposite sense of poetry, with the arsis being the upbeat, or unstressed note preceding the downbeat.