Both name and structure are Italian in origin, "sonetto" being the diminutive of "suono," sound. Dante and Petrarch knew it as a special lyric form intended for musical accompaniment. It must have fourteen lines, neither more nor less, with five beats or "stresses" to the line. Each line must end with a rhyme. In the arrangement of the rhymes the sonnet is made up of two parts, or rhyme-systems: the first eight lines forming the "octave," and the last six the "sestet." The octave is made up of two quatrains and the sestet of two tercets. There is a main pause in passing from the octave to the sestet, and frequently there are minor pauses in passing from the first quatrain to the second, and from the first tercet to the last.
Almost all of Petrarch's sonnets follow this rhyme-scheme: for the octave, a b b a a b b a; for the sestet, either c d e c d e or c d c d c d. This strict "Petrarchan" form has endured for six centuries. It has been adopted by poets of every race and language, and it is used to-day as widely or more widely than ever. While individual poets have constantly experimented with different rhyme-schemes, particularly in the sestet, the only really notable invention of a new sonnet form was made by the Elizabethans. Puttenham's Arte of English Poesie (1589) declares that "Sir Thomas Wyatt the elder and Henry Earl of Surrey, having travelled into Italy and there tasted the sweet and stately measures and style of the Italian poesie,… greatly polished our rude and homely manner of vulgar poesie…. Their conceits were lofty, their style stately, their conveyance cleanly, their terms proper, their metre sweet and well-proportioned, in all imitating very naturally and studiously their Master Francis Petrarch."
This is charming, but as a matter of fact both Wyatt and Surrey, with natural English independence, broke away from the strict Petrarchan rhyme form. Wyatt liked a final couplet, and Surrey used a rhyme-scheme which was later adopted by Shakspere and is known to-day as the "Shaksperean" form of sonnet: namely, three quatrains made up of alternate rhymes—a separate rhyme-scheme for each quatrain—and a closing couplet. The rhymes consequently run thus: a b a b c d c d e f e f g g. To the Petrarchan purist this is clearly no sonnet at all, in spite of its fourteen five-beat, rhyming lines. For the distinction between octave and sestet has disappeared, there is a threefold division of the first twelve lines, and the final couplet gives an epigrammatic summary or "point" which Petrarch took pains to avoid.
The difference will be still more clearly manifest if we turn from a comparison of rhyme-structure to the ordering of the thought in the Petrarchan sonnet. Mark Pattison, a stout "Petrarchan," lays down these rules in the Preface to his edition of Milton's Sonnets: [Footnote: D. Appleton & Co., New York, 1883.]
"a. A sonnet, like every other work of art, must have its unity. It must be the expression of one, and only one, thought or feeling.
"b. This thought or mood should be led up to, and opened in the early lines of the sonnet; strictly, in the first quatrain; in the second quatrain the hearer should be placed in full possession of it.
"c. After the second quatrain there should be a pause, not full, nor producing the effect of a break, as of one who had finished what he had got to say, and not preparing a transition to a new subject, but as of one who is turning over what has been said in the mind to enforce it further.
"d. The opening of the second system, strictly the first tercet, should turn back upon the thought or sentiment, take it up and carry it forward to the conclusion.
"e. The conclusion should be a resultant, summing the total of the suggestion in the preceding lines, as a lakelet in the hills gathers into a still pool the running waters contributed by its narrow area of gradients.
"f. While the conclusion should leave a sense of finish and completeness, it is necessary to avoid anything like epigrammatic point. By this the sonnet is distinguished from the epigram. In the epigram the conclusion is everything; all that goes before it is only there for the sake of the surprise of the end, or dénouement, as in a logical syllogism the premisses are nothing but as they necessitate the conclusion. In the sonnet the emphasis is nearly, but not quite, equally distributed, there being a slight swell, or rise, about its middle. The sonnet must not advance by progressive climax, or end abruptly; it should subside, and leave off quietly."