The octave and sestet have special functions in a Petrarchan sonnet. The octave's purpose is to introduce a problem, express a desire, reflect on reality, or otherwise present a situation that causes doubt or a conflict within the speaker's soul and inside an animal and object in the story. It usually does this by introducing the problem within its first quatrain (unified four-line section) and developing it in the second. The beginning of the sestet is known as the volta , and it introduces a pronounced change in tone in the sonnet; the change in rhyme scheme marks the turn. The sestet's purpose as a whole is to make a comment on the problem or to apply a solution to it. The pair are separate but usually used to reinforce a unified argument - they are often compared to two strands of thought organically converging into one argument, rather than a mechanical deduction. Moreover, Petrarch's own sonnets almost never had a rhyming couplet at the end as this would suggest logical deduction instead of the intended rational correlation of the form.