In a Shakespearean sonnet, there are fourteen lines of iambic pentatmenter, consisting of three quatrains and a rhyming couplet. In this type of sonnet, the poet typically presents a problem or premise in the first twelve lines (the three quatrains) followed by a solution or conclusion in the last two lines, the rhyming couplet. Shakespeare's sonnets are grouped into three themes:
- "The brevity of life"
- "The transience of beauty"
- "The trappings of desire"
Sonnet 147 is a sonnet addressed to the "dark lady" that has desire and its "trappings" as the main idea, or theme. The tone of this sonnet is brooding and dark as the poet's desire finds itself becoming a sickness; it is "as a fever." This longing grows out of control: "Feeding on that which doth preserve the ill." For, the poet becomes mad with desire, even to the point of ignoring all reason, represented by the physician. In fact, "Desire is death"--this, then, is the problem of the first twelve lives.
The solution to this all-consuming and deadly desire is found in the final rhyming lines, the couplet: The poet realizes that he must be mad with love because somehow he has found his lady "fair," and has been enchanted by this vixen when she is really reckless and been unfaithful, "black as hell and dark as night."