In sonnet 18, Philip Sidney employs a conceit, or extended metaphor, throughout the poem. Metaphor is direct comparison of unlike things for effect. The speaker, Astrophil, uses numerous financial metaphors to support an overall comparison between money and behavior. This conceit is established in the first two lines as Astrophil speaks about “checks” and “Reason’s audit” and in the third line as he calls himself “a bankrupt.” With “checks,” however, he is also making a pun through reference to its meaning of restraint. Astrophil continues along these lines by talking about what was “lent” to him, and declares himself unable to behave properly, or “pay… Nature’s rent” which he owes “by birthright.” His “wealth” is his “youth,” which he has “spent” and “waste[d].” This continues into the ending, as the speaker refers twice to what he will “lose” for the sake of Stella’s love.
Sidney also uses personification within this conceit; both Reason and Nature are presented as humans capable of doing things such as conducting an audit or renting a space. He also personifies various traits he has, treating each one of them as a representation of his complete self; thus, he combines personification with synecdoche, the substitution of a part for the whole. “My youth doth waste, my knowledge brings forth toys, / My wit doth strive….” These clauses also use parallelism, the repetition of the same structure, and asyndeton, the omission of conjunctions.