The sonnet is an extremely rigid form of poetry. From Mary Oliver’s Rules for the Dance (discussed previously):
The Petrarchan sonnet, fourteen lines long, is made up of two parts, an eight-line section (octave) followed by a six-line section (sestet). These two parts may be, but are not always, separated by a line of space. In usual practice, the octave sets forth a situation, or a question; the sestet “solves” it, or in some cohesive or or resonant way comments upon this original premise. The rhyme scheme of the Petrarchan sonnet is exact and difficult. The octave pattern is a,b,b,a—that is, the eight-line octave operates with two rhyming sounds. The sestet’s design varies, it may be c,d,e c,d,e or c,d,c d,c,d.
The sonnet is slightly less rigid in the English or Shakespearean version, which loosens these patterns somewhat. It is still a poem of fourteen lines and it is still written traditionally in iambic pentameter. But the design of the rhyme is less fearsome; the English or Shakespearean sonnet is composed of three quatrains and a final couplet. Thus, with an occasional variation in the third quatrain, the pattern is a,b,a,b c,d,c,d e,f,e,f g,g.
The fact that Mary Oliver describes the Shakespearean sonnet’s rhyme pattern as “less fearsome” than its “exact and difficult” Romance counterpart aptly conveys the rigor of this poetic form.
Such specificity makes me wonder how the sonnet came to be—did it evolve naturally, as folk poetry does? If so, what forces shaped it? Why the final sestet and not, say, a quatrain? Or, perhaps, the sonnet was invented, maybe by Petrarch himself—but if it was, what made it stick?
The answer may lie in the sonnet itself:
So much has been said—memorably—within [the sonnet’s] mere fourteen lines! The form is comfortably recognizable. The composure of the pentameter; the progression of thought through the quatrains; the “turn” between octave and sestet, as though back into a mirror; the extravagance and yet applicability of its imagery—these are all unforgettable. After a little reading of sonnets, we count the lines no more, but feel what is being said developing toward a wholeness, and know, reliably, when it has come.