There are four essential elements that distinguish metrical verse from free verse or prose, ie, rhythm, meter, rhyme (rime) and alliteration.
The rhythm of a poem is the recurrence of stresses and pauses within. The poet can produce it by doing any of several things: making the intervals between his stresses fixed or varied, long or short; indicating his pauses (cesura or caesura, which is often marked by double lines) within his lines; end-stopping lines or running them over; writing in short or long lines. Rhythm in itself cannot convey meaning. And yet if a poet's words have meaning, their rhythm must be one with it.
Meter is expressed by stressed (or accented) and unstressed (or unaccented) syllable. The unit which is repeated to give steady rhythm to a poem is called a poetic foot, such as:
The iambic foot (or iamb) consists of an unstressed followed by a stressed syllables.
The trochaic foot (trochee) consists of an stressed followed by an unstressed syllable.
The anapestic foot (anapest) consists of two unstressed followed by an stressed syllable.
The dactylic foot (dactyl) consists of a stressed followed by two unstressed syllables.
Iambic and anapestic meters are called rising meters because their movement rises from unstressed to stressed; trochaic and dactylic meters are called falling.
The line lengths are conventionally described as:
Monometer (one foot)
Dimeter (two feet)
Trimeter (three feet)
Tetrameter (four feet)
Pentameter (five feet)
Hexameter (six feet)
Heptometer (seven feet)
Octameter (eight feet)
3. Rhyme (rime)
Rhyme consists of a repetition of accented sounds in words at the end of verse line. If the rhyme sound is the very last syllable of the line (eg, rebound, sound), the rhyme is called masculine; if the accnted syllable is followed by an unaccented syllable (eg, hounding, bounding), the rhyme is called feminine.
Rhymes amounting to three or more syllables, like forced rhymes, generally have a comic effect in English, and have been freely used for this purpose. Rhymes occurring within a single line are called internal (eg, Mary, Mary, quite contrary). Eye rhymes are words used as rhymes which alike but actually sound different (eg, alone, done; remove, love). Off rhymes (sometimes called partial, imperfect, or slant rhymes) are occasionally the result of pressing exigencies or lack of skill, but are also, at times, used deliberately by modern poets for special effects (eg, years, yoours; tigress, progress).
Poetic assertions are often dramatized and reinforced by means of alliteration - that is, the use of several nearby words or stressed syllables beginning with the same consonant - for example: pious, priestcraft, polygamy.
Assonace, or repetition of the same or similar vowel sounds within a passage (ussually in accented syllables), also serves to enrich it - for example: drowsily, drown, soul.
A related device is consonance, or the repetition of a pattern of consonants with changes in the intervening vowels - for example: linger, longer, languor; rider, reader, raider, ruder.
Direct verbal imitation of natural sounds (known as onomatopoeia) has been much attempted. Often ingeniously exploited as a side effect, onomatopoeia is essentially a trick, with about the same value in poetry as it has in music.
Polysallables, being pronounced fast, often cause a line to move swiftly; monosyllables, especially when heavy and requiring distinct accents, may cause it move heavily.