Possibilities for patterns abound in poems, because much of the effect is visual. You have, in a poem, sentences suspended in between white spaces on a page, and it makes a difference where and how a line ends to be succeeded by another line. One of the easiest patterns to recognize, after metrical rhythms, is rhyme (the practice of putting two or more words that have assonant vowel sounds and similar consonants at the end of lines in a recognizable pattern), and it has a long history. If the rhyming words are both one syllable long, it’s a masculine rhyme; if not, it’s called a feminine rhyme. If the rhymed words have the same consonants, but different vowel sounds, that’s called consonance (like litter & letter, wade & wood). Half or slant rhyme is any imperfect rhyme which uses proximate, though not perfectly rhyming words to set up a pattern (room / worm / warm). To name the pattern of rhyme, assign a different letter to each differently rhymed line: “Westron Wind,” for example, has the rhyme scheme abcb. Once you’ve found the rhyme scheme (if any), you’re ready to consider whether the stanza form fits into any extra-poetic patterns. For example, if the stanza has fourteen lines, it’s a sonnet (period). There are various subgenres of sonnets, including the Shakespearean (or English) and the Petrarchan (or Italian) sonnet. The English sonnet has three quatrains and a closing couplet (abab cdcd efef gg); the Italian sonnet has an octet of two braced quatrains (which means it has non-alternating rhymed lines, in this case abbaabba) and a sestet of six (cdecde or cdccdc). Other stanza forms exist, and they are numerous. The trick is not to memorize them all, but to look them up when you come across an unfamiliar poem you suspect is in dialog with another poem.
Other patterns include the auditory ones: alliteration (one or more words beginning with the same sound in close succession of one another; a more specific variety is sibilance, alliteration with the letter ‘s’), internal rhyme and assonance, and the familiar onomatopoeia, words whose pronunciation approximates their own meaning (hiss, sizzle). The sound-sense features of poetry can be particularly maddening if an essay-writer uses them to back up a preexisting argumentative point without reflecting on the role the auditory feature plays in the overall tone of the piece. For example, Richard Wilbur’s poem “The Barred Owl” includes two entirely different types of sibilance as the speaker describes a parent’s effort to sooth a child after hearing a scary hoot:
Words, which can make our terrors bravely clear,
Can also thus domesticate a fear,
And send a small child back to sleep at night,
Not listening to the sound of stealthy flight
Or dreaming of some small thing in a claw,
Borne up to some dark branch and eaten raw.
These lines give the lie to the idea that sibilance is always comforting and soothing, since the line including “small” and “sleep” is followed immediately by the one including the much creepier “sound” and “stealthy” (which remind us of the hoot that woke her in the first place), and then the “some small thing” being devoured. In all cases, the point is not only to recognize any of these patterns, but to come to some conclusion as to the relevance of your finding. What does it mean that some words are rhymed with others? Or that particular groups of words call attention to themselves because they sound alike? If you find a rhyme scheme or other pattern in a poem, but can’t figure out how that pattern contributes to the overall meaning of the poem, don’t assume that it’s interesting evidence, and consider dropping it from your reading. Conversely, if you note that the rhyme scheme of the stanza seems to emphasize data that contradicts your reading of the poem, change your reading! The argument that incorporates and accounts for the most evidence within a text without buckling is the best argument.