Metaphor in Sonnet 18
Metaphor Examples in Sonnet 18:
"thou grow'st,..." See in text (Sonnet 18)
The use of “grow’st” at the end of the line reveals an additional interpretation of “lines.” The poem itself, with its power to immortalize the youth, attaches him to time as if he were a scion, a grafted plant shoot. Thus “eternal lines” can take on a literal reference to tree branches. This metaphor evokes once again the thematic use of the natural world while deepening the idea of poetry as procreation.
"nature's changing course..." See in text (Sonnet 18)
Fairness fades as a result of both accidental decay as well as “nature’s changing course”—in other words, aging. The use of “untrimm’d” draws on a nautical metaphor: the adjustment, or trimming, of sails to fight the direction of the wind. Thus the “rough winds” in line 3 are reiterated, once again representing the unrelenting forces of nature.
"lease..." See in text (Sonnet 18)
“Lease” is an example of the financial metaphors that occur throughout Shakespeare’s Sonnets. The legal language of this metaphor implies a bad deal: the summer’s “lease” was “all too short” and this bad deal causes the summer to be ephemeral. This negative depiction of summer is later contrasted by the positive depiction of the youth’s “possession” of fairness in line 10.