“Sonnet 138” is an English sonnet, and more specifically, a Shakespearean sonnet. Most sonnets, in both English and Italian, have 14 lines. However, the rhyme scheme differs in Italian and English sonnets. Shakespeare uses the rhyme scheme ABAB CDCD EFEF GG in this and most of his other sonnets. The ending couplet (the final two lines that rhyme with one another) makes an English sonnet stand out from an Italian sonnet. Overall, Shakespearean sonnets have four sections: three quatrains (groups of four lines) and one couplet.

Italian sonnets, which are the predecessors of English sonnets, have an octave and a sestet. An octave is two quatrains, and the sestet is a group of six lines. The rhyme scheme of the Italian octave is ABBA ABBA. The rhyme scheme of the sestet can be CDE CDE or CDC DCD. Petrarch made the Italian sonnet popular a couple hundred years before Shakespeare wrote his sonnets. While Petrarch’s sonnets have a cruel mistress who rejects her lover, Shakespeare’s sonnets include a Dark Lady who is intimate with the speaker. In “Sonnet 138,” this is described with the words “I lie with her and she with me” (Line 13).