One objection to this method is that it produces, as you see, a rhymed couplet in the midst of the sestet.
The octet was finished and the first two lines of the sestet.
But there is a tendency to vary the rhyme scheme in the sestet—the octave usually is unchanged.
One of these must be in the octave and the other in the sestet.
I confess, though, that I did not know that Petrarch had made so frequent use of the 2-rhyme sestet.
The more important chamber compositions include a sestet for piano and strings, a trio, and a sonata for violincello and piano.
But there are many verse writers who use the couplet, unrelated in rhyme to the rest of the sestet, to conclude the sonnet.
It is divided into two parts: the first consisting of an octave or double quatrain, and the other of a sestet.
While following the Italian rime-schemes, however, he was not careful to observe any division between octave and sestet.
The rhymes of the first two quatrains are usually the same; those of the sestet are variously arranged.