What is it?
Allusion is a literary device in which the writer or speaker refers either directly or indirectly to a person, event, or thing in history or to a work of art or literature.
Why is it important?
Allusion connects the content of a text with the larger world. Allusion calls to mind the ideas and emotions associated with a well-known event or published work. Those ideas and emotions then contribute to what the author conveys.
How do I do it?
Refer either directly or indirectly to a well-known work of literature or an historical person or event.
"Four score and seven years ago our fathers brought forth on this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal."—Abraham Lincoln, the Gettysburg Address
Note: Here, Lincoln refers to the American Revolution using an allusion to the date 1776, the year the Declaration of Independence was signed. Four score and seven years ago means eighty-seven years, since a score is twenty years. Eighty-seven years earlier than 1863 is 1776.
"She was almost ready to go, standing before the hall mirror, putting on her hat, and he, his hands behind him, appeared pinned to the door frame, waiting like Saint Sebastian for the arrows to begin piercing him."—Flannery O'Connor, "Everything That Rises Must Converge"
Note: O'Connor compares her character with the religious figure Saint Sebastian in order to call to mind the idea of martyrdom associated with Saint Sebastian's story.