Mechanics of Verse
In poetry, metre (meter in American English) is the basic rhythmic structure of a verse or lines in verse. Many traditional verse forms prescribe a specific verse metre, or a certain set of metres alternating in a particular order. The study of metres and forms of versification is known as prosody. (Within linguistics, "prosody" is used in a more general sense that includes not only poetical metre but also the rhythmic aspects of prose, whether formal or informal, which vary from language to language, and sometimes between poetic traditions.) Qualitative vs. quantitative metre
The metre of much poetry of the Western world and elsewhere is based on particular patterns of syllables of particular types. The familiar type of metre in English-language poetry is called qualitative metre, with stressed syllables coming at regular intervals (e.g. in iambic pentameter, typically every even-numbered syllable). Many Romance languages use a scheme that is somewhat similar but where the position of only one particular stressed syllable (e.g. the last) needs to be fixed. The metre of the old Germanic poetry of languages such as Old Norse and Old English was radically different, but still was based on stress patterns. Many classical languages, however, use a different scheme known as quantitative metre, where patterns are based on syllable weight rather than stress. In dactylic hexameter of Classical Latin and Classical Greek, for example, each of the six feet making up the line was either a dactyl (long-short-short) or spondee (long-long), where a long syllable was literally one that took longer to pronounce than a short syllable: specifically, a syllable consisting of a long vowel or diphthong or followed by two consonants. The stress pattern of the words made no difference to the metre. A number of other ancient languages also used quantitative metre, such as Sanskrit and Classical Arabic (but not Biblical Hebrew). Feet
In many Western classical poetic traditions, the metre of a verse can be described as a sequence of feet, each foot being a specific sequence of syllable types — such as relatively unstressed/stressed (the norm for English poetry) or long/short (as in most classical Latin and Greek poetry). Iambic pentameter, a common meter in English poetry, is based on a normative sequence of five iambic feet or iambs, each consisting of a relatively unstressed syllable (here represented with "×" above the syllable) followed by a relatively stressed one (here represented with "/" above the syllable) — "da-DUM" = "× /" : × / × / × / × / × /
So long as men can breathe, or eyes can see,
× / × / × / × / × /
So long lives this, and this gives life to thee.
This approach to analyzing and classifying metres originates from ancient Greek tragedians and poets such as Homer, Pindar, Hesiod, and Sappho. Note that some metres have an overall rhythmic pattern to the line that cannot easily be described using feet. This occurs in Sanskrit poetry; see Vedic metre and Sanskrit metre). (Although this poetry is in fact specified using feet, each "foot" is more or less equivalent to an entire line.) However, it also occurs in some Western metres, such as the hendecasyllable favoured by Catullus, which can be described as: x x - u u - u - u - -
(where "-" = long, "u" = short, and "x x" can be realized as "- u" or "- -" or "u -") Half-lines
In place of using feet, alliterative verse of old Germanic languages such as Old English and Old Norse divided each line into two half-lines. Each half-line had to follow one of five or so patterns, each of which defined a sequence of stressed and unstressed syllables, typically with two stressed syllables per line. Unlike typical Western poetry, however, the number of unstressed syllables could vary somewhat. For example, the common pattern "DUM-da-DUM-da" could allow between one and five...