In Shakespeare's Sonnet 18, what is the metaphor in the line "When in eternal lines to Time thou grow'st"?

This line from Shakespeare's Sonnet 18 contains layers of meaning. Since the entire poem to this point has referred to summer and nature, and this line speaks of growing as the opposite of death, the metaphor is that the woman the poet is addressing will continue to grow like a treesince the poem will keep her alive, nurturing her always. Although any living thing can grow, in the context of the poem where the...

This line from Shakespeare's Sonnet 18 contains layers of meaning. Since the entire poem to this point has referred to summer and nature, and this line speaks of growing as the opposite of death, the metaphor is that the woman the poet is addressing will continue to grow like a tree since the poem will keep her alive, nurturing her always. Although any living thing can grow, in the context of the poem where the writer mentions "darling buds of May" and "shade," a tree seems most appropriate for the metaphorical meaning.

Another metaphor is apparent in the line, and that is the reference to "Time." The capitalization of the word suggests Shakespeare wishes to personify time. In the poem, the woman being immortalized by the poem grows "to Time"; that is, in the sight or perspective of Time, she continues to live on and thrive. It is as if Time is an audience, or possibly a parent, watching the woman grow over the years. What is meant literally is that future generations of living people will see the woman continue to grow in reputation as she becomes more and more revered through the centuries because of the sonnet that has been written in her honor.

Another way of looking at this reference to "Time" is to understand it as metonymy, a figure of speech in which an item is named for something with which it is closely associated—such as saying "life" instead of "blood" or "flesh" instead of "humanity." Here "Time" is used as a substitute for "future generations of people," who will live in the time to come.

This line from Shakespeare's sonnet contains two metaphors as well as metonymy.