The Petrarchan form has a two-part structure.
• The octave (the first 8 lines), usually rhyming abbaabba, establishes the speaker’s situation.
• The sestet (the last 6 lines), usually with the rhyme scheme cdcdcd or cdecde, resolves, draws conclusions about, or expresses a reaction to the speaker’s situation.
The Petrarchan sonnet has been called organic in its unity because the octave and sestet fit together naturally. Unity is also produced by the rhyme scheme, which involves only four or five different rhyming sounds.
The Shakespearean form also has 14 lines but is structured differently.
• Three quatrains (stanzas of 4 lines) are followed by a rhyming couplet (2 lines).
• The rhyme scheme is abab cdcd efef gg.
• The first quatrain introduces a situation, which is explored in the next two quatrains. The third quatrain (or sometimes the final couplet) usually includes a turn, or shift in thought. The couplet resolves the situation.