The theme of appearance vs. reality is used all throughout the play and there are many instances in which something appears to be real but in actuality is something completely different. Listed below are a few instances:
One instance of appearance vs. reality occurs when Don Pedro dons a mask and pretends to be Claudio to woo Hero in Claudio's name. Hero has no idea whom she is talking to; she believes it is probably Don Pedro who is courting her because her father earlier encouraged her to accept should he ask for her hand. We see Leonato declare to Antonio that he will prepare Hero for Don Pedro's courtship in the lines, "I will acquaint my daughter withal, that she may be the better prepared for an answer" (I.ii.19-20). The reality of this situation is that Don Pedro is actually himself, but he is courting Hero not for his own sake, but for Claudio's.
Another instance of appearance vs. reality is that Don John tricks Claudio into believing that Don Pedro has deceived him and is actually courting Hero for himself. We see Don John deceiving Claudio in this regard when we see Don John tell him that Don Pedro is in love with Hero, as we see in his lines, "He is enamoured on Hero. I pray you dissuade him from her; she is no equal for his birth" (II.i.142-143). The reality is that Don Pedro is courting Hero on Claudio's behalf, just like he promised. Another reality is that Don Pedro may actually be in love with Beatrice, as we see him propose to her in this scene, but she turns him down (288).
A third instance of appearance vs. reality is that Don John tricks Claudio a second time, this time making him believe that Hero has been unfaithful. He deceives Claudio by pretending that Margaret, who is seen in Hero's window at midnight with Borachio, is actually Hero. The reality is that Hero is actually still very chaste and innocent.