The older sense of the word in relation to the four humours.The outward appearance of the face as compared with the sun ('the eye of heaven') in the previous line, or.'Complexion' in line six, can have two meanings: In this view, it can be seen as part of a transition to sonnet 20's time theme. Some scholars, however, contend that it is part of the procreation sonnets, as it addresses the idea of reaching eternal life through the written word, a theme they find in sonnets 15– 17. It is also the first of the cycle after the opening sequence now described as the procreation sonnets. The poem is part of the Fair Youth sequence (which comprises sonnets 1–126 in the accepted numbering stemming from the first edition in 1609). = ictus, a metrically strong syllabic position. So long as men can breathe or eyes can see, (18.13) The couplet's first line exemplifies a regular iambic pentameter rhythm:

It also contains a volta, or shift in the poem's subject matter, beginning with the third quatrain.

Petrarchan sonnets typically discussed the love and beauty of a beloved, often an unattainable love, but not always. The poem reflects the rhetorical tradition of an Italian or Petrarchan Sonnet. It also has the characteristic rhyme scheme: ABAB CDCD EFEF GG. Sonnet 18 is a typical English or Shakespearean sonnet, having 14 lines of iambic pentameter: three quatrains followed by a couplet. There is an irony being expressed in this sonnet: it is not the actual young man who will be eternalized, but the description of him contained in the poem, and the poem contains scant or no description of the young man, but instead contains vivid and lasting descriptions of a summer day, which the young man is supposed to outlive. The speaker then states that the Fair Youth will live forever in the lines of the poem, as long as it can be read.

He also notes the qualities of a summer day are subject to change and will eventually diminish. In the sonnet, the speaker asks whether he should compare the Fair Youth to a summer's day, but notes that he has qualities that surpass a summer's day, which is one of the themes of the poem. ' Sonnet 18' is one of the best-known of the 154 sonnets written by the English playwright and poet William Shakespeare.

Sonnet 18 iambic pentameter uses