The speaker opens the poem with a question addressed to the beloved: "Shall I compare thee to a summer's day?" The next eleven lines are devoted to such a comparison. In line 2, the speaker stipulates what mainly differentiates the young man from the summer's day: he is "more lovely and more temperate." Summer's days tend toward extremes: they are shaken by "rough winds"; in them, the sun ("the eye of heaven") often shines "too hot," or too dim. And summer is fleeting: its date is too short, and it leads to the withering of autumn, as "every fair from fair sometime declines." The final quatrain of the sonnet tells how the beloved differs from the summer in that respect: his beauty will last forever ("Thy eternal summer shall not fade...") and never die. In the couplet, the speaker explains how the beloved's beauty will accomplish this feat, and not perish because it is preserved in the poem, which will last forever; it will live "as long as men can breathe
This sonnet is certainly the most famous in the sequence of Shakespeare's sonnets; it may be the most famous lyric poem in English.
Among Shakespeare's works, only lines such as "To be or not to be" and "Romeo, Romeo, wherefore art thou Romeo?" are better-known. This is not to say that it is at all the best or most interesting or most beautiful of the sonnets; but the simplicity and loveliness of its praise of the beloved has guaranteed its place.
On the surface, the poem is simply a statement of praise about the beauty of the beloved; summer tends to unpleasant extremes of windiness and heat, but the beloved is always mild and temperate. Summer is incidentally personified as the "eye of heaven" with its...