What are the main themes in Hamlet?

Uncertainty: Hamlet wishes to avenge his father and punish both his mother and uncle, but he does not know the moral or proper way to achieve justice.
Fortune or Chance: Hamlet could not save his father. No matter how carefully he plots his revenge, chance events lay waste to his plans. In Act 3, Scene 1, Hamlet believes his uncle is hiding behind the curtains in his mother’s room. In fact, however, the person who is hiding is Polonius, Ophelia’s father. Hamlet kills him and sets off an unanticipated chain of events.
Mortality: Hamlet is grief-stricken by the loss of his father. When he comes upon Yorick’s skull, Hamlet realizes the permanency of death. He thinks of all the great men who have come before him and not a single one has escaped death.
“Alexander died, Alexander was buried, Alexander returneth / into dust; the dust is earth; of earth we make loam; / and why of that loam, whereto he was converted, might / they not stop a beer barrel? / Imperious Caesar, dead and turn'd to clay / Might stop a hole to keep the wind away”