What defining feature distinguishes an Italian sonnet from other sonnet forms?

The defining feature that distinguishes an Italian sonnet, also known as a Petrarchan sonnet, is the presence of a sestet. An Italian sonnet is characterized by its structure, which typically consists of an octave followed by a sestet. The octave usually presents a problem, situation, or emotional state, while the sestet provides a resolution or reflection on the octave. This distinct division is crucial because it shapes the thematic development throughout the poem.

In contrast, options related to rhyme schemes or metric forms do not uniquely define the Italian sonnet. For instance, the rhyme scheme of aabbcc is more characteristic of other types of poetry rather than the Italian sonnet, which commonly features an abbaabba pattern in the octave. Additionally, while iambic tetrameter can be used in various poetic forms, the Italian sonnet traditionally employs iambic pentameter, making the meter not a unique identifier. Lastly, the length of 10 lines is inaccurate, as the Italian sonnet comprises 14 lines in total. Thus, the presence of a sestet is the feature that accurately identifies the Italian sonnet among other sonnet forms.