The Petrarchan sonnet, also known as the Italian sonnet, is a sonnet named after the Italian poet Francesco Petrarca, although it was not developed by Petrarch himself, but rather by a string of Renaissance poets. Because of the structure of Italian, the rhyme scheme of the Petrarchan sonnet is more easily fulfilled in that language than in English. The original Italian sonnet form consists of a total of fourteen hendecasyllabic lines (in English sonnets, iambic pentameter is used) in two parts, the first part being an octave and the second being a sestet.
The rhyme scheme for the octave is typically ABBAABBA. The sestet is more flexible. Petrarch typically used CDECDE or CDCDCD for the sestet. Some other possibilities for the sestet include CDDCDD, CDDECE, or CDDCCD (as in Wordsworth's "Nuns Fret Not at Their Convent's Narrow Room," a sonnet about sonnets). This form was used in the earliest English sonnets by Wyatt and others. For background on the pre-English sonnet, see Robert Canary's web page, The Continental Origins of the Sonnet. In a strict Petrarchan sonnet, the sestet does not end with a couplet, since this would tend to divide the sestet into a quatrain and a couplet. However, in Italian sonnets in English, this rule is not always observed, and CDDCEE and CDCDEE are also used.
The octave introduces a problem or conflict in the mind of the speaker, in the first four lines (known as the first quatrain). The next quatrain explains the problem or provides an exposition to the reader. The sestet begins with a volta which marks the change in rhyme scheme as well as the change of the conflict into a solution or some form of resolution.
Sir Thomas Wyatt and Henry Howard, Earl of Surrey are both known for their translations of Petrarch's sonnets from Italian into English. While Surrey tended to use the English sonnet form in his own work, reserving the Petrarchan form for his translations of Petrarch, Wyatt made extensive use of the Italian sonnet form in the poems of his that were not translation and adaptation work.