Twelfth Night’s major preoccupation is the difference between appearance and reality. Viola, one of the major characters of the play dresses as a boy and becomes Cesario.
This false appearance earns her entry into the court of Duke Orsino. When one is a woman, society restricts her in many ways but Viola as Cesario enjoys freedom differently.
When Olivia falls in love with her, we come to know how superficial is the idea of love in human beings. They fall in love with mere appearance many times and bring on the tragedy.
In Elizabethan theatre, men used to play the role of women so Shakespeare subverts the whole tradition by making a woman acting like a man. This alteration of reality makes us rethink the whole concept of what is reality and what is an illusion.
When Olivia falls in love with Cesario, Viola feels sad about her situation and says that “she were better love a dream.” Yet it is a play where such a dream comes true because Sebastian looks like in reality what Viola looks like in disguise.
On the other side, Viola is Cesario for Orsino so even when she is in love with him, she can not express it to him. Her reality as Viola is actually Cesario in appearance.
Malvolio becomes a laughing stock due to his appearance. His pompous self makes him a source of comedy. He believes in the false letter and dresses as what he is not.
He wears something so offending that Feste, Maria and other characters take advantage of it and condemn him to a dark room to torture him further. His humiliating tragedy is also the result of the contrast between appearance and reality.
When the play starts straightening out the confusion between appearance and reality, we see a return to truth. The play teaches us the harms of falseness. Feste shows himself as a fool but is actually very wise.
His reality and appearance are actually deliberate wisdom on his part. In the play, we see the passage of its major character from illusion to reality. The contrast between appearance and reality is what constitutes the course of the play.