“Sonnet 18″ by Williams Shakespeare can be described as one long metaphor, where the person speaking makes a comparison between his beloved and a summer’s day. He goes on to emphasize that his beloved is more *temperate” than the summer, which he describes as having “rough winds”.
The line, “Shall I compare thee to a summer’s day?” goes on all through the poem. With the like, the speaker, Shakespeare, describes his beloved as being lovelier than the extent of the comparison.
He also says that his beloved has a better complexion than the sun that often fades, implying that his beloved would always retain her youth and vitality to him. More than that, he declares that his beloved will always have her young glow, no matter how much time passes.
The line “… But thy eternal summer shall not fade” is metaphorical, and is used to symbolize her eternal youth.