Dramatic irony exists when the audience knows more than a character knows in a dramatic scene. How does the duke’s statement to Brabantio, that whoever beguiled his daughter will be punished, create dramatic irony?

Light and dark are juxtaposed in the Duke's declaration to Brabantio, that "if virtue no delighted beauty lack/ your son-in-law is far more fair than black." Black is associated with sin, evil, and darkness; these negative things are also associated to black people, merely because of the color of their skin. The Duke's statement is ironic, since Othello is black, but truthful, because his soul is good and light. Light/white/fairness all convey innocence, goodness, etc.; any symbol that is white has these qualities. The juxtaposition of black and white, light and dark shows up again and again in the play, as the colors become symbolic within the story.