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I quote: "For instance, when a structuralist critic analyzes Robert Browning's "My Last Duchess", she wouldn't isolate the poem as a liberal humanist would do. She feels that the only way to truly understand the poem is to put it in a larger context, to take into consideration other 19th century poetry, to understand the events that inspired this poem, to understand Browning's background, etc. If language is a structure of arbitrary signs, then the structuralism believe that language isn't a true reflection of the world (Barry, 42)."
Try these sites for a start: "My Last Duchess" - Analysis
My Last Duchess: Study Guide