The speaker in Sonnet 18 by Petrarch uses negative words and phrases throughout the sonnet to express the fact that he was unable to put in words how gorgeous his beloved one was.
During the time he wrote this sonnet he was passing by a writers' block and he was incapable to show his beloved Laura how beautiful he thought she was by words so he repeats in many ways that there's nothing that can describe, capture or equal her beauty.
