One theme that is very present in Act IV is madness. Hamlet's constant sense of feigned madness is still present in this Act, particularly when Hamlet is describing what he has done with Polonius' body. His twisted words and confusing directions make it appear if he is both insane and dangerous, prompting Claudius to quickly begin the process of sending him to England. Another, more genuine sense of madness is portrayed through Ophelia, after learning of the death of her father. This also pulls in the theme of appearance versus reality because some of Hamlet's madness is an act put on for his own purposes, while Ophelia's genuine madness is so deep and forceful that it leads her to an untimely death.
-Sam Slug