A catalectic line is a line of poetry that is not complete in rhythm, missing a syllable at the end or ending with a part of a rhythm unit that is not finished. One type of catalexis is called headlessness, which happens when the first syllable, which is not stressed, is left out of the line.

A line that is missing two syllables is referred to as brachycatalectic. A line that has one extra syllable is called hypercatalectic.

In English

Poems can be written using lines that are shorter than usual, lines that are complete, or a mix of both, as shown in the carol written by Cecil Frances Alexander in 1848. In this carol, the lines with 7 syllables are shorter than usual.

It has been argued that in many Indo-European languages, when shorter and complete lines are used together, the shorter lines are often placed at the end of a section or group of lines.

Blunt and pendant catalexis

Catalexis can be divided into two types. (Here, "x" represents an anceps syllable.)

An example of a line ending with a short syllable becoming longer in catalexis is found in Goethe's poem Heidenröslein, or in the English carol Good King Wenceslas, which uses the same meter.

Another example is the children's song Here We Go Round the Mulberry Bush. The first stanza ends as follows:

In these songs, when music is added, the second-to-last syllable is made longer to balance the two lines. However, there is not enough evidence to show if this happened in Ancient Greek.

When a poem is shortened by two syllables (called brachycatalectic), the ending that was already short remains short.

Quantitative metres

In languages that use measured rhythms, such as Latin, Ancient Greek, Arabic, Persian, and Sanskrit, the final syllable of any line is called "anceps," meaning it can be either long or short. One ancient view suggests that even if the final syllable is short in pronunciation, it is treated as long because of the pause that follows it (known as "brevis in longo"). Therefore, a line ending with a short syllable followed by a long one (x – u –) becomes u – x when it is shortened (catalectic).

An example in Ancient Greek is the iambic tetrameter, which has both normal and catalectic forms. In classical Arabic, the most common rhythm, the ṭawīl, also has normal and catalectic forms. In Sanskrit, comparing the traditional śloka with the mandākrāntā rhythm shows the same pattern of shortening. The first line of the Bhagavad Gita follows the śloka rhythm, while the mandākrāntā rhythm is structured differently. A similar pattern appears in classical Persian, such as the choriamb rhythm (– u u –), which has a shortened version. In Latin and Greek, the rarely used trochaic octonarius rhythm is not shortened, but the more common trochaic septenarius rhythm is. The anapaestic octonarius and anapaestic septenarius rhythms differ in that when the final syllable is removed, the last part must be a long syllable, not two short ones (as seen in the metres of Roman comedy).

In ancient Greek

Catalexis was often found in the poetry of ancient Greece and Rome, as well as in ancient Sanskrit verse. Catalectic endings are especially common in lines with dactylic ( – u u ), trochaic ( – u ), or anapestic ( u u – ) rhythms. These endings are frequently used at the end of a section or period in a poem, so much that acatalectic lines (which are not missing a syllable) rarely end a section. In classical poetry, the last syllable of a line was always considered long. If a dactyl ( – u u ) becomes catalectic, it changes into a spondee ( – – ), which has two long syllables instead of one long and two short.

Ancient poetry was often performed with music, and the type of music used for catalectic endings is a topic of interest. A few ancient Greek poems have survived with actual musical notes. Four of these were written by Mesomedes, a poet from the early second century CE. In two of his poems, To Helios and To Nemesis, the catalectic meter used is called apokrota, meaning "sonorous." In these poems, the missing syllable is often marked with symbols that indicate a longer note. In two parts of To Helios, this appears to be a musical technique called a melisma, which uses three notes instead of one. This suggests that ancient poets may have used catalexis to signal a change in melody or continued singing in place of the missing syllable.

In ancient Greek drama, catalectic meters may have been linked to a specific musical instrument called the aulos, played by a male musician known as an aulete. For example, in the surviving plays of Menander, most are written in iambic trimeters. However, in one long scene from his play Misanthrope, the meter changes to a 15-syllable catalectic iambic tetrameter, which was recited with the accompaniment of an aulos.

In Latin poetry

Poem 25 by Catullus uses a special type of meter called iambic tetrameter catalectic. Out of Catullus's surviving 114 or so poems and parts of poems, this meter is only found in this one poem.

In classical Persian

There are about 115 different metres used in Persian poetry, but most are not used often. Around 30 metres are commonly used. Most Persian metres are made up of repeating patterns of three, four, or eight syllables. This makes it easy to see that some metres are catalectic, meaning the last part of the metre has one fewer syllable than the others. For example:

The first four metres listed above have 11 syllables each and are often used in long masnavi poems, which are written in rhyming couplets, such as Ferdowsi’s Shahnameh. Longer metres are used for lyric poems. However, one masnavi metre has only 10 syllables:

Bruce Hayes suggests a rule to explain this. He says that when a pattern ends with two short syllables ("uu"), both are omitted at the end of the line, making the metre catalectic.

Catalexis in music

The hymn Pange lingua by Venantius Fortunatus uses a meter called trochaic tetrameter catalectic, which was also used in the marching chants of Roman armies. This hymn is one of the oldest with surviving musical notation.

Greek meter terms are often used to describe musical phrasing. Some well-known examples include:

• The slow movement of Haydn's Surprise Symphony (spondaic dimeter catalectic)
• The theme of Weber's Rondo brillante in E-flat (anapestic tetrameter brachycatalectic)
• The slow movement of Beethoven's 7th symphony (alternating acatalectic and catalectic dactylic tetrameter)