The Italian or Petrarchan sonnet consists of two parts; an octave and a sestet. The octave can be broken down into two quatrains; likewise, the sestet is made up of two tercets. The octave presents an idea to be contrasted by the ending sestet.The particular quatrains and tercets are divided by change in rhyme.he octave can be broken down into two quatrains; likewise, the sestet is made up of two tercets. The octave presents an idea to be contrasted by the ending sestet. The particular quatrains and tercets are divided by change in rhyme.