My masters are you mad? Or what are you? Have you
no wit, manners, nor honesty, but to gabble like
tinkers at this time of night? (II.iii.)

Here, Malvolio admonishes Sir Toby and Sir Andrew for their drunken rowdiness. He even goes so far as to suggest that their roguish behavior and blatant disregard for others is a sign of madness. Malvolio’s attitude becomes significant as later in the play, Sir Toby enacts his revenge on Malvolio by making him appear mad in Olivia’s company, essentially forcing on Malvolio some of his own medicine, albeit in a much larger dose. Madness has a more liberal sense here, and seems to include anything that falls outside the bounds of civil order.

Sir Topas, never was a man thus wronged. Good Sir
Topas, do not think I am mad. They have laid me here
in hideous darkness. (IV.ii.)

These lines are spoken by Malvolio once he has been imprisoned as a madman. In order to exploit the joke even further, Sir Toby pressures Feste to dress up as a priest and perform a mock-exorcism on Malvolio. The reference to darkness here is significant as it not only refers to the physical darkness of the prison itself but is also a figurative allusion to madness as a state of confusion. Indeed, Malvolio is not the one who is mad (as he rightly points out) but those around him; everything has been turned upside down. Civility has been pushed aside so that other characters in Twelfth Night can freely indulge in silly antics and ribaldry.

I am as mad as he,
If sad and merry madness equal be. (III.iv.)

In these lines Olivia suggests that she is as mad as Malvolio, who has been acting quite strangely after reading Maria’s letter. However, Olivia makes a distinction here. Her “madness” functions as an expression of her love for Cesario, which remains unreturned and has plunged her into a state of deep melancholy. Hers is a gloomy madness, essentially stemming from a state of lovesickness, while Malvolio’s is a merry kind, and originates instead from an over-inflated optimism, as he is convinced that Lady Olivia really loves him. This line is important as it links the theme of madness to lovesickness and melancholy, and suggests that romantic desire has the power to inhibit rational decision making. In this way, the many raucous antics of Twelfth Night speak to the enormous influence of love and erotic desire in this play.