Traditionally, poems follow a rhyme scheme. This usually means the last words in two or more lines contain similar sounds, such as "sky" and "eye." However, rhymes also can be internal, which entails a word in the middle of a line rhyming with the word at the end, as in "I silently laugh at my own cenotaph." Rhymes do not always have to be exact. "Eye rhymes" have similar spellings but different pronunciations, as in "ear" and "bear." Rhymes with feminine endings end on unstressed syllables, while masculine endings fall on stressed syllables.
The meter of a poem determines the number of syllables in a line of poetry. English speakers naturally stress certain parts of words and rush the others, as in "today," where "to" is rushed and "day" is stressed. A "foot" denotes one unit of a stressed and unstressed pattern. For example, one foot of "iambic" denotes a rushed syllable followed by a stressed syllable, as in "today," while "anapestic" contains two rushed syllables followed by a stressed syllable, as in "The Assyrian came down like a wolf on the fold." Because this line contains four "feet" of anapestic meter, it is an "anapestic tetrameter."
Genre governs the rhyme and meter of a poem. For example, the Shakespearean sonnet follows iambic pentameter, which means every line contains 5 feet of unstressed/stressed units, for a total of 10 syllables per line. Ballads contain quatrains, a stanza of four lines, that alternate between iambic tetrameter and iambic trimester.
Poetic genres also govern the content of a poem. Sonnets express love toward an object of affection. Odes extol a certain subject, such as a hero or a victory at war, for example. However, odes do not follow any given rhyme or meter scheme, although they often contain intricate structures. Epics traditionally do not rhyme either. Epics narrate the story of a hero who performs a mighty feat. (See Reference 1)
Not all poems follow predetermined structures or topics, however. Free verse poetry allows poets to write freely, creating line breaks, stanza breaks, metric stresses and rhymes where they wish. Free verse poems can contain a structure or scheme, but generally free verse poems do not maintain such structures consistently. Free verse poetry appeals to many contemporary poets, both amateur and experienced, as it allows for the greatest artistic freedom.
In addition to structures, poets also can incorporate poetic devices into their poems for effect. Common poetic devices include alliteration, where words in succession begin with the same letters, such as smooth as silk; assonance, repetition of vowel sounds, such as thin sticks; hyperbolic exaggeration, such as hungry enough to eat a horse; and imagery and simile, such as fast as the wind. All of these devices create complexity in poetry, not only enhancing a reader's intellectual experience but creating interesting tactile sensations.