What does Hamlet decide to do at the end of this speech? ("O what a rogue and peasant slave am I") Act 2, Scene 2

has been
paralyzed by indecision over whether or not to obey 's commands to kill .hesitates because is
unsure whether the ghost is a devil sent to lure him into evil or truly the ghost of his father.
After he sees the player so movingly act out Hecuba's grief, Hamlet, who feels genuine grief for
the death of his father, is spurred into action. He decides that a play that enacts a murder
just like the one the ghost described would so shock Claudius, if he were guilty, that he would
betray himself. Hamlet is behaving here rationally and logically: he doesn't want to have
innocent blood on his hands, and it does make sense to run an experiment to see if Claudius is
guilty. As Hamlet says of the ghost, it:

May be the
devil, and the devil hath power

T' assume a pleasing shape. Yea, and
perhaps

Out of my weakness and my melancholy,

As
he is very potent with such spirits,

Abuses me to damn me.

In other words, the devil may well be playing on Hamlet's intense
grief to lure him into finding a false scapegoat for his father's death, in order to 'damn'
Hamlet. Evil spirits, he says know, how to play on people's weaknesses.

 

Hamlet thus decides that he will find more solid (relative)
grounds to stand on than the hearsay of a spirit: 

Ill
have grounds

More relative than this. The plays the thing

Wherein Ill catch the conscience of the king.