Recognition of some of the literary devices enhance our appreciation of the poem. The dominant metaphor is the beloved is a "summer's day." The first two lines make an assertion, and the colon indicates that the succeeding 2 lines explain why the beloved is more "temperate"--less volatile--in that he lacks "rough winds"--a metaphor for emotional turmoil--and the beloved is also better than "summer" (usually considered a perfect time of year) because summer is only borrowed time (leased). The "eye of heaven" in line 5 is the sun, and the personification of the sun continues by giving him a "gold complexion." "Ow'st" (owns) in line 10 contrasts with "leased" in line 4, and the personification of death, by means of capitalizing it and giving it the quality to brag, becomes the antagonist over which the beloved wins out. The "grow'st" in line 12 gives the beloved more qualities of nature. Then, in the concluding couplet, the poet has the power of nature in that he can give life to his beloved through the poetry he writes.
Anthony Hecht in his introduction to Blakemore Evans’s edited collection of Shakespeare’s sonnets argues that ‘Sonnet 18 “[…] is decisively Petrarchan, notwithstanding its Shakespearean rhyme scheme. To begin with, it is rhetorically divided into octave and sestet, the change between the two parts balanced on the fulcrum of the word but at the beginning of the ninth line.” (See The New Cambridge Shakespeare, p.9) Shakespeare’s ‘Sonnet 18’, therefore, can be interpreted from another perspective. The first eight lines (the Petrarchan octave) offer a comparison between the beloved’s beauty and a summer’s day. Shakespeare claims that his beloved is more beautiful than a summer’s day and argues that beauty from summer and nature “declines” as time progresses. In the last six lines (the Petrarchan sestet) Shakespeare notes why and how the beloved’s beauty will remain “eternal”. Shakespeare claims that his lines are “eternal” and in his “eternal lines” the beloved’s beauty will remain unchanged in perpetuity.
Sonnet 18 is one of Shakespeare's most well-known and recognized pieces of poetry.
The first quatrain is a comparison of a young man to a summer's day-and the outcome is "thou art more lovely and more temperate". The young man is perfection, and outdoes even nature. The poet is unable to give adequate crdeit to all the young man is.
The second quatrain describes the conditions that will affect such perfection. Time is fleeting, and perfection is not permanent. It is hard to remain perfect where mortals are concerned. The summer is only one season in the year, and this refers to the inevitable aging that will occur.
The last quatrain suggests that through this poem, the young man will achieve immortality. The poet has written lines that will keep the young man alive in the minds of the reader. "So long lives this, and gives life to thee".