Of the 154 sonnets published in Shakespeare’s famous 1609 quarto, “Sonnet 18” is, by far, the most famous. The poem is one of the quarto’s first 126 sonnets, which address or discuss an unnamed figure termed the “Fair Youth” by scholars. This specific sonnet begins with the oft-quoted line: “Shall I compare thee to a summer’s day?” This iconic question comments on the Fair Youth's beauty and places it in natural contexts. Although written to praise his visage, the final couplet redirects the readers to the idea of the sonnet itself. The speaker praises the form for its capacity to preserve and explains that the sonnet has the power to immortalize that which must inevitably fade. Unlike the Petrarchan sonnet, composed of fourteen lines split across two stanzas, an octave and a sestet, the Shakespearean sonnet relies on a structure of three quatrains and a final couplet, where the volta or “final turn” of the sonnet occurs. 

The first quatrain introduces the sonnet’s defining question, speaking to the fair youth and asking if he, the speaker, should compare the youth’s appearance to a summer’s day. The speaker ponders if the comparison is apt but quickly rejects the supposition and provides several reasons that highlight the season’s fallibility as a metaphor for the youth’s beauty. Indeed, the speaker argues that the youth is “more lovely and more temperate” than such a day, meaning that the youth in question is of fairer appearance and consistent demeanor than a potentially volatile summer’s day. “Rough winds” impede the beauty of early summer in May and the season’s “lease” is short. Indeed, the speaker argues, this fair youth is nothing like the days of this unpredictable and brief season.

In the second quatrain, the speaker continues to list his qualms with such a comparison, presenting other reasons why summer is an inaccurate metaphor for the sonnet’s subject. Referring to the sun as the “eye of heaven,” the speaker explains that summer days might be too hot for comfort. Their “gold complexion” might also be marred by bad weather and their beauty “dimm’d.” Though often “fair,” summer days are vulnerable to “chance or nature’s course,” and their unpredictability means their fairness is volatile and inconsistent: nothing like the speaker’s fair youth. 

By comparison, as the third stanza indicates, the youth’s beauty will never fade nor mar. It is a constant truth, an “eternal summer” unaffected by time or nature. The summer of youth will not ebb nor will the subject lose possession of his appearance. The speaker tells the youth that even “death” cannot “brag thou wander’st in his shade,” for no end shall ever reach his beauty nor shall he succumb to Death’s embrace. The final line of the quatrain, “When in eternal lines to time thou grow’st,” shifts the tone of the poem. It is not the youth himself who shall live on in beauty; indeed, the speaker’s lines alone immortalize him, preserving that which, much like a summer’s day, will fade. Physically, the youth’s beauty will wane. However, it is sealed forever in these lines, a feat only the speaker can accomplish.

In the final couplet, the speaker completes the tone shift. The sonnet remains on the subject of the youth’s loveliness, but the speaker writes in praise of his ability to communicate it long after it is lost. His work is a monument to the beloved and his beauty, and in his lines alone will he live on. For as long as men live and read, these lines act as amber, preserving his visage for all time. In so doing, the speaker “gives life” to the youth, rendering him immortal and unburdened by the demands of time. The sonnet deters death and, instead, grants him eternity.