Diction, or a writer's choice of words, has a particularly important place in poetry, as the meaning, sound, and number of syllables in each word is often very important. Diction in poetry defines the tone and many aspects of the style of a given poetic work. In many cases, particularly in poems that must conform to rigid stylistic constraints, the poet must pick words that contain a certain number of syllables and that rhyme with other specific words. Diction is important even in less structured works of poetry as well, as most poetic forms are far less wordy than most works of prose. While a prose writer can often spend several paragraphs on description, a poet often needs to convey a significant piece of information about something in only a few well-chosen words.
Many poems are written in highly-structured forms that must conform to specific rules. In heroic couplets, for instance, the poet must write in iambic pentameter, with five stressed and five unstressed syllables arranged in an alternating manner. Furthermore, the end syllables of each pair of lines must rhyme. Within these restraints, diction becomes extremely important, as the poet must choose words that fit these restraints without compromising the meaning that he wishes to convey. Each word must be assessed based on its meaning and its role in the rhythm and rhyme scheme.
Diction in poetry is also incredibly important because of its ability to convey tone. Words conveying ideas of dreariness, darkness, and melancholy will convey a drastically different tone than those suggestive of joy, brightness, and energy. The tone of a poem is often used to influence its emotional impact beyond the literal meanings and sounds of the words. A skilled poet crafts his diction not only to convey a certain meaning and to sound a certain way, but also to evoke a particular set of emotional responses from readers. Sloppy and careless diction in poetry may succeed in meaning and sound, but is likely to fail to evoke the specific emotional response intended by the poet.
In some forms of poetry, particularly in narrative poems, the choice of words is used to tell the reader something about the narrator. Diction in poetry can be used to convey that the speaker is from a certain background or age group, for instance. This use of diction, though much more common in prose, still has an important place in many forms of poetry, particularly when the identity of the speaker is essential to fully understanding the poem.