Arsis and thesis
[3] However, in discussions of Latin and modern poetry the word arsis is generally used to mean the stressed syllable of the foot, that is, the ictus.
[4] Since the words are used in contradictory ways, the authority on Greek metre Martin West[5] recommends abandoning them and using substitutes such as ictus for the downbeat when discussing ancient poetry.
[7] The ancient Greek writers who mention the terms arsis and thesis are mostly from rather a late period (2nd-4th century AD), but it is thought that they continued an earlier tradition.
However, in other Greek writers from Plato onwards, the word basis referred to the whole foot (i.e. the sequence of arsis and thesis).
[14] More frequently Aristoxenus refers to arsis and thesis respectively as the "up time" (ὁ ἄνω χρόνος, ho ánō khrónos) and the "down time" (ὁ κάτω χρόνος, ho kátō khrónos), or simply the "up" (τὸ ἄνω, tò ánō) and the "down" (τὸ κάτω, tò kátō).
Especially in instrumental music, this must have included a dynamic element, so that it makes good sense to transcribe the larger rhythmical units by means of modern bars.
The Roman writer Marius Victorinus (4th century AD), in part of his work attributed to a certain Aelius Festus Aphthonius, gave both definitions when he wrote: "What the Greeks call arsis and thesis, that is raising and putting down, indicate the movement of the foot.
Arsis also means the elatio ("elevation") of a time-duration, sound or voice, thesis the placing-down (depositio) and some sort of contraction of syllables.
[19] Aristides refers to the sequence (– ⏑ ⏑) not as a dactyl but as ἀνάπαιστος ἀπὸ μείζονος (anápaistos apò meízonos) (i.e. an anapaest "starting from the greater") and regards it as consisting of a thesis followed by a two-syllable arsis.
[24] In the Seikilos epitaph, a piece of Greek music surviving on a stone inscription from the 1st or 2nd century AD, the notes on the second half of each six-time-unit bar are marked with dots, called stigmai (στιγμαί).
According to a treatise known as the Anonymus Bellermanni these dots indicate the arsis of the foot; if so, in this piece the thesis comes first, then the arsis: According to Tosca Lynch, the song in its conventional transcription of 6/8 rhythm corresponds to the rhythm referred to by ancient Greek rhythmicians as an "iambic dactyl" (δάκτυλος κατ᾽ ἴαμβον (dáktulos kat᾽ íambon) (⏑⏔ ⁝ ⏑⏔) (using the term "dactyl" in the rhythmicians' sense of a foot in which the two parts are of equal length) (cf.
[27] In Mesomedes' Hymn to the Sun, on the other hand, which begins with an anapaestic rhythm (⏑⏑– ⏑⏑–), the two short syllables in each case are marked with dots, indicating that the arsis comes first:[28] In some of the short examples of music in the Anonymus Bellermanni treatise the dots marking the arsis are found not only above notes but also above rests in the music.
Tosca Lynch writes: "Differently from rhythmicians, metricians employed the term arsis to indicate the syllables placed at the beginning of a foot or metrical sequence; in such contexts, the word thesis designated the syllables appearing at the end of the same foot or metrical sequence."
"[31] 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.
A fugue per arsin et thesin these days generally refers to one where one of the entries comes in with displaced accents (the formerly strong beats becoming weak and vice versa).
