1. Catalyst for the plot: The ghost's appearance and revelation of his murder by Claudius kickstart the entire plot. Hamlet's desire for revenge becomes the central driving force of the play, leading to a chain of events that ultimately culminate in tragedy.
2. Source of information and motivation: The ghost provides Hamlet with vital information about his father's murder, revealing Claudius's guilt and the circumstances surrounding the crime. This knowledge fuels Hamlet's desire for justice and motivates his subsequent actions.
3. Symbol of the past and unresolved conflict: The ghost represents the unresolved past, specifically the unresolved conflict between Hamlet's father and Claudius. His presence serves as a constant reminder of the injustice that has been done and the need for retribution.
4. Exploration of themes of revenge and morality: The ghost's presence raises questions about the morality of revenge and the consequences of acting upon it. Hamlet wrestles with the ethical dilemma of whether or not to avenge his father's death, highlighting the complex and ambiguous nature of justice.
5. Metaphor for the supernatural and the unseen: The ghost is a manifestation of the supernatural, representing the unseen forces that can influence human actions and destinies. His appearance underscores the play's exploration of the limits of human knowledge and understanding.
6. Device for dramatic effect: The ghost's presence creates suspense, mystery, and psychological tension throughout the play. His dramatic entrances and pronouncements contribute to the overall atmosphere of intrigue and impending doom.
7. Symbol of the "undivulged" truth: The ghost's knowledge of the murder, hidden from everyone else, makes him a symbol of the "undivulged" truth that only he knows. This adds to the play's exploration of the unreliability of appearances and the difficulty of discerning the truth.
In essence, the ghost in Hamlet is more than just a spectral figure. He is a crucial element of the play's narrative, thematic exploration, and overall dramatic effect. His presence serves as a catalyst for the plot, a source of information and motivation, and a powerful symbol of the play's central themes.