Perhaps the most vital element of sound in poetry is rhythm. Often the rhythm of each line is arranged in a particular meter. Different types of meter played key roles in Classical, Early European, Eastern and Modern poetry. In the case of free verse, the rhythm of lines is often organized into looser units of cadence. Robinson Jeffers, Marianne Moore, and William Carlos Williams were three notable poets who rejected the idea that meter was a critical element of poetry, claiming it was an unnatural imposition into poetry.
Poetry in English and other modern European languages often uses rhyme. Rhyme at the end of lines is the basis of a number of common poetic forms, such as ballads, sonnets and rhyming couplets. However, the use of rhyme is not universal. Much modern poetry avoids traditional rhyme schemes. Classical Greek and Latin poetry did not use rhyme. Rhyme did not enter European poetry until the High Middle Ages, when adopted from the Arabic language. Arabs have always used rhymes extensively, most notably in their long, rhyming qasidas. Some classical poetry forms, such as Venpa of the Tamil language, had rigid grammars (to the point that they could be expressed as a context-free grammar), which ensured a rhythm. Alliteration played a key role in structuring early Germanic and English forms of poetry, alliterative verse. The alliterative patterns of early Germanic poetry and the rhyme schemes of Modern European poetry include meter as a key part of their structure, which determines when the listener expects instances of rhyme or alliteration to occur. Alliteration and rhyme, when used in poetic structures, help emphasise and define a rhythmic pattern. By contrast, the chief device of Biblical poetry in ancient Hebrew was parallelism, a rhetorical structure in which successive lines reflected each other in grammatical structure, sound structure, notional content, or all three; which lent itself to antiphonal or call-and-response performance.
Sound plays a more subtle role in free verse poetry by creating pleasing, varied patterns and emphasizing or illustrating semantic elements of the poem. Alliteration, assonance, consonance, dissonance and internal rhyme are among the ways poets use sound. Euphony refers to the musical, flowing quality of words arranged in an aesthetically pleasing way.
Poetry depends less on linguistic units of sentences and paragraphs. The structural elements are the line, couplet, strophe, stanza, and verse paragraph.
Lines may be self-contained units of sense, as in the well-known lines from William Shakespeare’s Hamlet:
To be, or not to be: that is the question.
Alternatively a line may end in mid-phrase or sentence:
Whether ’tis nobler in the mind to suffer
this linguistic unit is completed in the next line,
The slings and arrows of outrageous fortune.
This technique is called enjambment, and is used to create expectation, adding dynamic tension to the verse.
In many instances, the effectiveness of a poem derives from the tension between the use of linguistic and formal units. With the advent of printing, poets gained greater control over the visual presentation of their work. As a result, the use of these formal elements, and of the white space they help create, became an important part of the poet’s toolbox. Modernist poetry tends to take this to an extreme, with the placement of individual lines or groups of lines on the page forming an integral part of the poem’s composition. In its most extreme form, this leads to concrete poetry.
Rhetorical devices such as simile and metaphor are frequently used in poetry. Aristotle wrote in his Poetics that “the greatest thing by far is to be a master of metaphor”. Since the rise of Modernism, some poets have opted for reduced use of these devices, attempting the direct presentation of things and experiences. Surrealists have pushed rhetorical devices to their limits, making frequent use of catachresis.