Sonnet 15 serves as part of the transition between the earlier Procreation Sonnets, in which the speaker urges the addressee to have children and thus "copy" himself to achieve immortality, and later sonnets in which the speaker emphasizes the power of his own 'eternal lines" (18.12) to immortalize the addressee. Stephen Booth, professor emeritus at the University of California Berkeley, notes that the "dividing line between the procreation sonnets and sonnets 18-126" has a curious "imperceptibility," but he goes on to assert that Sonnet 15's closing line "As he Time takes from you, I engraft you new" (15.14) is the "first of several traditional claims for the immortalizing power of verse." This theme of poetic immortality is continued in later sonnets, including sonnet 17's closing couplet "You should live twice: in child and in my rhyme," in sonnet 18's last few lines "Nor shall death brag thou wander'st in his shade / When in eternal lines to time thou grow'st. / So long as men can breathe or eyes can see, / So long lives this, and this gives life to thee," and sonnet 19's final line "My love shall in my verse live ever young."