The octave and the sestet are usually found in a manner in which they contrast each other. The Shakespearean sonnet however, follows a different pattern and setting as it is not divided merely into two parts but into four parts. If one was to examine the structure, it would be evident that the first three parts are our lines long and are named as quatrains; following the rhyme sequence of ABAB. The last part is defined as the couplet and follows a rhyme sequence of CC.
The Shakespearean sonnet is used more often for the purposes of developing a theme or a metaphor of ideas. The quatrain part usually contains the ideas while the couplet part usually contains the summary or a new presentation of the ideas.