Purpose of "madness" in Hamlet?
Is there truly a compelling reason for Hamlet's ruse of madness? He has ample opportunity to kill Claudius without this laborious and convoluted plan. Argue for or against, using textual evidence.
When Hamlet first aappears in Act 1, Scene 2, King Claudius shows that he already is suspicious of him and intends to keep him a virtual prisoner.
For your intent
In going back to school in Wittenberg,
It is most retrograde to our desire:
And we beseech you, bend you to remain
Here, in the cheer and comfort of our eye,
Our chiefest courtier, cousin, and our son.
This is before Hamlet has any intention of acting against the King. Hamlet is a scholar and only wants to go back to the university. He knows, however, that Claudius is trying to pry into his soul, because it is natural for the King to suspect that Hamlet would be angry about being passed over for his father's crown. Claudius is projecting his own thoughts onto his stepson. He has the power to have Hamlet executed without a trial. He is afraid of Hamlet and Hamlet is afraid of him. This contest of wills and wits goes on throughout the play. Claudius enlists Polonius, Gertrude, Ophelia, Rosencrantz, Guildenstern, and no doubt many others to spy on Hamlet. At one point Claudius uses a beautiful metaphor to express his fears and suspicions:
There's something in his soul,
O'er which his melancholy sits on brood;
And I do doubt the hatch and the disclose
Will be some danger (III.1)
Hamlet feels that his life is in danger if Claudius comes to regard him as a threat. This is before Hamlet even meets with the Ghost. Now, when he learns that his stepfather murdered his father and usurped the throne, he feels that this knowledge is so volatile that it will be hard for him to conceal his new attitude from the man who is so zealous and so expert in spying on him and cross-examining him. It is not until right after his meetinig with the Ghost that he expresses his intention to pretend to be mad. He swears Marcellus and Horation to secrecy:
Here, as before, never, so help you mercy,
How strange or odd soe'er I bear myself,
As I perchance hereafter shall think meet
To put an antic disposition on,
That you, at such times seeing me, never shall,
With arms encumber'd thus, or this headshake,
Or by pronouncing of some doubtful phrase,
As 'Well, well, we know,' or 'We could, an if we would,'
Or 'If we list to speak,' or 'There be, an if they might,'
Or such ambiguous giving out, to note
That you know aught of me: this not to do,
So grace and mercy at your most need help you, Swear. (I.5)
Presumably he meets with the others who have seen the Ghost and swears them to secrecy too. Secrecy is of the utmost importance. If the King suspected that Hamlet was having meetings with his own father's ghost, he would take drastic action. He is not above committing murder himself, as he has demonstrated by poisoning Hamlet's father.
As Lady Macbeth tells her husband:
Only look up clear.
To alter favor ever is to fear.
Hamlet is in a tough spot--especially for a courtier. He has been hiding his contempt as well as his disapproval of his uncle's marriage to Gertrude. Now he must hide his hatred, his knowledge of Claudius' villainy, and his own intention and obligation to assassinate him. If he makes specific plans to kill the king and claim the throne, he must hide those from the King's prying eyes and from those of his spies, including especially Polonius, Rosencrantz, and Guildenstern.
It does seem plausible that Hamlet might decide to pretend to be mad in order to account for possible slips of the tongue, odd body language, and other changed behavior. He has a very dangerous and wily enemy.