Өлең жолындағы екпінді және екпінсіз буындар

Accented and unaccented parts of a poetic foot, respectively, in prosody

[[File:Arsis and thesis breathe. png|thumb|Binary and ternary rhythms and meter are said to originate in human movement. are respectively 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. 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. Since the words are used in contradictory ways, the authority on Greek metre Martin West recommends abandoning them and using substitutes such as ictus for the downbeat when discussing ancient poetry. However, the use of the word ictus itself is very controversial.

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. For example, it is believed that Aristides Quintilianus (3rd or 4th century AD) adopted much of his theory from Aristotle's pupil Aristoxenus (4th century BC), who wrote on the theory of rhythm. Arsis ("raising") and thesis ("putting down or placing") originally seem to have meant the raising and lowering of the foot in marching or dancing. A Greek musicologist, Bacchius or Baccheios (c. 4th century AD), states: "What do we mean by arsis? When our foot is in the air, when we are about to take a step. And by thesis? When it is on the ground." Aristides Quintilianus similarly writes: "Arsis is the upwards motion of a part of the body, while thesis is the downwards motion of the same part." And in general Aristotle (4th century BC) wrote: "All walking (poreia) consists of arsis and thesis." Because of the association between rhythm and stepping, the parts of a rhythmic sequence were referred to as "feet". Aristides Quintilianus (3rd or 4th century AD) writes: "A foot is part of an entire rhythm from which we recognise the whole. It has two parts: arsis and thesis." 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). More frequently Aristoxenus refers to arsis and thesis respectively as the "up time" (ὁ ἄνω χρόνος, ) and the "down time" (ὁ κάτω χρόνος, ), or simply the "up" (τὸ ἄνω, ) and the "down" (τὸ κάτω, ). The division of feet into "up" and "down" seems to go back at least as far as the 5th century Damon of Athens, teacher of Pericles. Stefan Hagel writes: "Although the significance of the ancient conception [of upbeat and downbeat] and the applicability of the modern terms are disputed, there is no doubt that arsis and thesis refer to some type of accentuation actually felt by the ancients. 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."

However, writers discussing poetic metre seem to have used the terms arsis and thesis in a different way. 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." (Lynch (2016), p. 506.) 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 the later works of Latin writers on metre, the arsis is invariably considered the first part of the foot (see below). A Greek work on metre compiled in the 13th century AD, the Anonymus Ambrosianus, refers the words arsis and thesis to a whole line: "Arsis refers to the beginning of a line, thesis to the end."

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 natura, 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. Contradicting this, however, Julian of Toledo (Iulianus Toletanus) (7th century AD) writes: "In three syllable words, if the first syllable has the accent, as in dominus, the arsis claims two syllables and the thesis one; but when the accent is on the penultimate, as in beatus, the arsis has one syllable and the thesis two." Similar statements are found in Terentianus Maurus, Aldhelm, and other grammarians. In disassociating arsis from raised pitch, these writers clearly use the terms in a different way from pseudo Priscian. In their writings, arsis means the first half of a word, and thesis the second half; if the penultimate syllable in a three syllable word is accented, the second half is deemed to begin at that point.

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. 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). An example is the bass line at bar 37 of no. 17 Book 2 of Bach's Das Wohltemperierte Clavier. In the past, however, a fugue per arsin et thesin could also mean one where the theme was inverted.

Ancient Greek ἄρσις ársis "lifting, removal, raising of foot in beating of time", from αἴρω aírō or ἀείρω aeírō "I lift". The i in aírō is a form of the present tense suffix y, which switched places with the r by metathesis. Ancient Greek θέσις thésis "setting, placing, composition", from τίθημι títhēmi (from root θε/θη, the/thē, with reduplication) "I put, set, place".