(2) As an examination of the rimes will show (a b b a a b b a: c d d e c
e), there is a natural metrical division at the end of the eighth line.
The first eight lines in technical language are called the "octave," the
last six lines are called the "sestet." The octave is sometimes said to
consist of two quatrains, and the sestet of two tercets.

(3) There is not only a metrical division between the octave and the
sestet, but the character of the thought also undergoes a subtle change
at that point. It is to be understood, of course, that in the whole poem
there must be both unity of thought and mood. Yet, at the ninth line,
the thought which is introduced in the octave is elaborated, and
presented as it were under another aspect. As Mr. Mark Pattison has
admirably expressed it: "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. 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. 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. The conclusion should be a resultant summing
the total of the suggestion in the preceding lines. . . . While the
conclusion should leave a sense of finish and completeness, it is
necessary to avoid anything like epigrammatic point."

(4) An examination of the rimes again will show that greater strictness
prevails in the octave than in the sestet. The most regular type of the
octave may be represented by a b b a a b b a, turning therefore upon two