This happens in Act 1, Scene 5, after the ghost has spoken to Hamlet and revealed that he is his father, the King. He tells Hamlet that he was murdered by his brother, Claudius, who then married Hamlet's mother, Gertrude. The ghost also reveals that he is now trapped in purgatory and cannot rest until his murder is avenged.
It is this revelation, specifically the ghost's desire for revenge, that convinces Hamlet that the ghost is not evil. Here's why:
* The ghost's identity: The ghost reveals itself as Hamlet's father, a figure Hamlet loved and respected deeply. This instantly makes the ghost more sympathetic and less likely to be a demonic trickster.
* The ghost's motive: The ghost's desire for justice and his longing for peace are understandable, even noble. This reinforces Hamlet's belief that the ghost is genuine and seeks to right a wrong.
* The ghost's character: The ghost is described as sorrowful, mournful, and burdened by his fate. This further adds to his credibility and convinces Hamlet that he is a real, suffering being.
While Hamlet still struggles with doubt and grapples with the implications of the ghost's revelation, he is ultimately convinced that the ghost is genuine and deserves his trust. This conviction drives him to seek revenge against Claudius, the murderer who has taken his father's life and his rightful place on the throne.