The structure of William Shakespeare's Sonnet 11, "As fast as thou shalt wane, so fast thou grow'st" is comprised both of repeated patterns of sound and of rhetorical patterns giving shape to the ideas and argument of the sonnet.
As is typical of Shakespeare's sonnets, Sonnet 11 takes the form of a Shakespearean or English sonnet. It consists of 14 lines of iambic pentameter. Its rhyme scheme consists of three open quatrains followed by a couple, i.e. ABAB CDCD EFEF GG.
As is also structurally typical of the Shakespearean sonnet, the poem is divided into three rhetorical parts with clear logical breaks or "turns" (Italian: "volta") between them. The first part, consisting of the first eight lines (or first two quatrains), sets out the premise that although humans are mortal, we live on in our children, expressed in the lines:
And that fresh blood which youngly thou bestow'st,
Thou mayst call thine when thou from youth convertest.
The focus shifts between the end of line 8 and the beginning of line 9, in the first of the two "turns" of the poem. The third quatrain (lines 9-12) emphasizes that while it doesn't matter if "harsh, featureless, and rude" people refrain from reproducing, it is the duty of those blessed with nature's bounty to pass it on to descendants.
Another minor turn occurs at the end of line 12, leading up to the conclusion that the addressee is so attractive that he should act as a "seal" stamping out copies by having many children.