The audience sees this as a harmless act of disguise, for the moment, although deceiving shouldn’t hurt people. We also see displays of deception as well for when Viola walks into Illyria, and meets Orsino, and later Olivia, they believe that she is a man. Orsino and Olivia are deceived in this act, which will affect their relationships towards her in the end of the play. The audience know this is so she can get close to him.
In act two we meet Viola’s identical twin brother, Sebastian, who thinks Viola is dead, and Malvolio persuses Cesario with Olivia’s ring. This is when Viola realises that Olivia likes Cesario. The three conspirators play a trick on Malvolio, to make him think that Olivia likes him, which affects his behaviour towards her.
All these acts of deception are all deceiving someone or another. First Cesario deceives Malvolio and Olivia in making him think that he is Cesario, and second is when Malvolio is deceived by the three conspirators (Maria, Fabian and Sir Toby). The effect of these deeds are that people think that Viola is a man and, soon Malvolio will approach Olivia dressed differently and Olivia will think that Malvolio is mad. The audience see this as a point that all the main plots start to take form. The audience also think that the deceiving characters are creul and manipulative to toy with other characters emotions and get away with it.
“I know this letter will make a contemplative idiot of him” (Act II v 16-17)
Maria says this, and this shows the audience that the characters dont think highly of Malvolio.
In act three, the audience see Sebastian and Antonio going to Illyria, and Antonio is giving Sebastian all of his money. Later when Antonio is arrested, he is with Cesario and wants him to bail him out. Cesario has never seen him before in his life and Antonio takes this the wrong way. This again is another case of Viola deciving people by pretending to be someone she is not. At Olivia’s house, Malvolio approaches Olivia who is shocked to see what he is wearing and how he is acting towards her, and so Maria declares that he is mad. He is acting this way in responce to Maria's letter, thinking that it was written by Olivia and trying to impress her.
“Lo, how hollow the fiend speaks within him” (Act III iv 90)
Malvolio shows self-deceit by pretending to be someone that he is not, just to impress Olivia. The audience think that this is a wrong thing to do because he is changing himself for another person and and you shoud be yourself. If that person you are trying to impress doesn't like who you are then you should not be together. Also Maria shows deception because she tells everyone that Malvolio is mad, and Malvolio is being lied to because he is told that Olivia loves him, by being purposely given the letter.
In this act, Maria is doing most of the deceiving, because she is telling everyone lies. She tells Malvolio that Olivia loves him, telling Olivia that Malvolio is mad, and telling herself that she is being reasonable in doing this.
"Pray god he not be bewitched" (Act 3 iv line 100)
The audience now think that Maria is not a very nice person and can be quite devious because she is always telling peole lies or tricking them into beliving something that isn't true. The effect of these characters is that Olivia gets a strong impression that Malvolio is mad, and Malvolio will be locked away.
"Good Maria, let this fellow be looked to." (Act III iv 57)
The audience are now also convinced that Malvolio is mad, as is all the characters in the play.
In act four, Sir Andrew mistakes Sebastian for Cesario and hits him but Olivia interrupts thinking that’s is Cesario, before anything else happens. Feste disguises himself as Sir Topas and confronts Malvolio, who is locked away, to make him believe he really is mad. Malvolio starts to doubt himself.
In this act, Sir Andrew shows self-deceit because he is pretending to be strong and tough, heroic man, by squaring up to Sebastian, although he knows that he isn’t. This is shown because he looses the fight. Sebastian shows deception, because he makes everyone think that he is Cesario. The result of these events is major confusion for all characters.
Later on the audience see a lot of deception, because Sebastian hits Andrew, and Cesario get accused, and doesn’t know why. This makes everyone confused because now strange things are happening and people are getting accussed of things that they haven't done. Also Feste shows deception because because he makes everyone think he is Sir Topas (except the conspirators).
In act five, Olivia and Sebastian get married. This again is deception because Sebastian has made Olivia belive that he is Cesario. Sir Toby and Sir Andrew claim that Cesairo injured Sir Andrew, when it was infact Sebastian.
“If a bloody coxcomb be a hurt you have hurt me” (Act V i 186)
The twins finally confront and realise that one another is alive, Viola reveals that she is a woman and Fabian, then tells the truth about Malvolio and that they played a trick on him, and Malvolio swears revenge on them all. This is self deceit becayse Malvolio belives that he can get revenge on them all but he knows deep down inside that he can't. The Duke and Viola get married and the play ends with a song from Feste.
“When that I was and a little tiny boy, with hey, ho, the wind and the rain…” (Act V I 385)
This adds empathy to the scene because it makes the audience feel sorry for Feste because everyone is happy and he isn't.
In this act Cesario and show self-deceit because they have their brother/sister in front of them and not know. Sebastain had an excuse, because his sister was in disguise but Viola must be stupid to have her brother in front of her and not recognise him.
"Sebastian was my father.
Such a Sebastian was my brother to." (Act 5 i line 228)
Sebastian shows deception because he makes everyone belive he is Cesario and doesn’t say anything to anyone.
“As I perceive she does, there’s something in’t, that is deceivable. But here the lady come” (Act V i )
The effect of this is that everything is resolved and goes back to normal and they all live happily. The audience see this as the final closing point to all the stories come to a close, and is the end of the play.
So to conclude, self-deceit and deception do take park in the play Twelfth Night a lot, and become main themes. I don’t think that the play would be very good without these themes because they are what make the play good and hold it together.