The rhythm of a sonnet is called iambic pentameter. An iamb refers to a pair of syllables in which the second syllable is stressed. A line of iambic pentameter consists of five iambs in a row, leading to a repetitive alternation of unstressed and stressed syllables. The third line of Shakespeare's sonnet 18 provides a clear example of iambic pentameter: "Rough winds do shake the darling buds of May." The stress falls on "winds," "shake," "dar-," "buds" and "May."
Sonnets are 14 lines long, usually divided into stanzas whose lengths depend on the style of sonnet. The classic English sonnet is divided into three quatrains and a couplet. A quatrain is a set of four lines, while a couplet is a set of two lines. The couplet at the end usually provides commentary or a twist on the subject of the rest of the poem. Other styles of sonnets divide the 14 lines differently, but maintain the same length.
An English sonnet has a set rhyme scheme organized by stanza. The first stanza has an ABAB rhyme scheme, meaning that the first and third lines rhyme with each other, and the second and fourth lines rhyme with each other, but not the first and third. The second and third stanzas have the same pattern with different rhymes, creating CDCD and EFEF patterns. The lines of the final couplet rhyme with each other but no other lines, indicated with GG.
While the Engish (or Shakespearean) sonnet has become one of the most widespread sonnet conventions, there are other variations on the style. An Italian (or Petrarchan) sonnet is divided into an octave (eight lines) and a sestet (six lines) with a rhyme scheme of ABBAABBA and either CDECDE or CDCCDC. A Spenserian sonnet is a variation of the English sonnet that uses a linked rhyme scheme, sharing rhymes between stanzas for a rhyme scheme of ABAB BCBC CDCD EE.