In the seventy-second and seventy-fourth sonnet we have the unusual schemes c d e e d c and c d e d e c. The worst form, according to the Italian critics, was that which ended in a rhyming couplet. This kind of ending, as we shall see later on, is one of the chief characteristics of the specifically English form of the sonnet.
The original and oldest form of the sonnet, however, as recent inquiries seem to show, was that with crossed rhymes both in the quatrains and in the terzetti, on the scheme a b a b a b a b c d c d c d. But this variety had no direct influence on the true English form, in which a system of crossed rhymes took a different arrangement.
An essential point, then, in the Italian sonnet is the bipartition, the division of it into two chief parts; and this rule is so strictly observed that a carrying on of the sense, or the admission of enjambement between the two main parts, connecting the eighth and ninth verse of the poem by a run-on line, would be looked upon as a gross offence against the true structure and meaning of this poetic form. Nor would a run-on line be allowed between the first and the second stanza; indeed some poets, who follow the strict form of the sonnet, do not even admit enjambement between the first and the second terzetto, although for the second main part of the poem this has never become a fixed rule.
The logical import of the structure of the sonnet, as understood by the earlier theorists, especially Quadrio, is this: The first quatrain makes a statement; the second proves it; the first terzetto has to confirm it, and the second draws the conclusion of the whole.
§ 308. The structure of this originally Italian poetic form may be illustrated by the following sonnet, equally correct in form and poetical in substance, in which Theodore Watts-Dunton sets forth the essence of this form of poetry itself:
The Sonnet’s Voice.
A metrical lesson by the sea-shore.
Yon silvery billows breaking on the beach
Fall back in foam beneath the star-shine clear,
The while my rhymes are murmuring in your ear