What are the poetic and literary devices used in the poem "Crazy Kate" by William Cowper?

In "Crazy Kate," Cowper uses personification to express the vicissitudes of fate to which Kate has been subjected. For example, in the beginning of the poem, he writes of a person who "better days / saw better clad, in cloak of satin trimmed / With lace." He makes "better days" the observer of Kate (and he also repeats the word "better" to emphasize Kate's decline). Later, he writes, "Her fancy followed him through foaming waves / To distant shores." In these lines, another example of personification, Cowper makes Kate's "fancy," or imagination, the subject of the action in which she is following her lost love, a sailor, to his destination. Cowper's use of personification stresses that Kate herself is hapless and can't follow her lost love, though she wants to. Instead, only her imagination can follow him. "Fancy" also "would oft anticipate his glad return," meaning that her imagination also believes falsely that he will come back. The poet's use of personification expresses the idea that her emotions and delusions are coming to take over her mind.

Later in the poem, Kate must spend her days alongside the shore and, "unless when Charity forbids, / The livelong night." In another use of personification, only "Charity" (meaning people's good will) can prevent Kate from being homeless day and night. The poet's use of personification to express charity also expresses that Kate is subject to the vicissitudes of fate and the whims of her fellow man to live. 

Cowper uses symbols, such as the "cloak of satin trimmed / With lace, and hat with splendid ribbon bound," to stand for Kate's sanity and better luck in earlier days. After her love is lost, her attire is described: "A tattered apron hides, / Worn as a cloak, and hardly hides a gown / More tattered still." Her clothes symbolize her decline, her inner pain, and her mental disintegration. As her clothes decline, so does she, mentally. Her clothes are the outward manifestation of her inner state. The "idle pin" that Kate begs from others is also a symbol of her mental decline, as she hordes the pins as if they were gold, but they serve no purpose. 

At the end of the poem, Cowper uses anaphora, or repetition of words at the beginning of clauses, in the lines: "Though pressed with hunger oft, or comelier clothes, / Though pinched with cold, asks never. Kate is crazed." The poet's repetition of the word "though" expresses that Kate is really oppressed by cold and hunger, but she never asks for food. Her extreme want, compared with what she asks for, shows her mental distress.