What is a summary of Shakespeare's Sonnet 18?
Shakespeare begins by comparing his beloved to a summer day. He says the beloved is more lovely than a day in summer because more consistently beautiful. A summer's day can be lovely, but it can also be windy and harsh, shaking the buds of the plants ready to burst into flower. The sun can be too hot or can move behind a cloud. Also, the season of summer doesn't last long enough:
summer’s lease hath all too short a date
Meaning, all too soon bad weather comes. The beloved, in contrast, lives in an "eternal summer" that will not fade as real summer does. Nor will death be able to brag that it has caught the beloved. This is because of the verses Shakespeare has written about his lover. These verses will never fade. They will immortalize the beloved for all time.
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Shakespeare's sonnet begins with a very straightforward question: "Shall I compare thee to a summer's day?" Then, there is a straightforward answer: "Thou art more lovely and more temperate." And, the rest of the sonnet supports his argument that the poet's love will remain constant while nature changes. For instance, in lines 7 and 8, the poet writes that nature changes its course and "every fair from fair sometimes declines." But, "thy eternal summer shall not fade." In other words, everything that nature produces--a summer's day, including--is transitory, but the poet's love is eternalized in verse. Summarizing his argument with the sonnet's couplet, the poet writes that as long as men can see and read, the beauty of his love shall be preserved in his verse.:
So long as men can breathe or eyes can see,
So long lives this and this gives life to thee.
Ironically, however, the subject of the sonnet receives immortality only because of the verse, and so, in a sense, the argument for the immortality of the loved one is somewhat flawed.