Themes are the fundamental and often universal ideas explored in a literary work.
What separates Hamlet from other revenge plays (and maybe from every play written before it) is that the action we expect to see, particularly from Hamlet himself, is continually postponed while Hamlet tries to obtain more certain knowledge about what he is doing. This play poses many questions that other plays would simply take for granted. Can we have certain knowledge about ghosts? Is the ghost what it appears to be, or is it really a misleading fiend? Does the ghost have reliable knowledge about its own death, or is the ghost itself deluded? Moving to more earthly matters: How can we know for certain the facts about a crime that has no witnesses? Can Hamlet know the state of Claudius’s soul by watching his behavior? If so, can he know the facts of what Claudius did by observing the state of his soul? Can Claudius (or the audience) know the state of Hamlet’s mind by observing his behavior and listening to his speech? Can we know whether our actions will have the consequences we want them to have? Can we know anything about the afterlife?
Many people have seen Hamlet as a play about indecisiveness, and thus about Hamlet’s failure to act appropriately. It might be more interesting to consider that the play shows us how many uncertainties our lives are built upon, how many unknown quantities are taken for granted when people act or when they evaluate one another’s actions.
Directly related to the theme of certainty is the theme of action. How is it possible to take reasonable, effective, purposeful action? In Hamlet, the question of how to act is affected not only by rational considerations, such as the need for certainty, but also by emotional, ethical, and psychological factors. Hamlet himself appears to distrust the idea that it’s even possible to act in a controlled, purposeful way. When he does act, he prefers to do it blindly, recklessly, and violently. The other characters obviously think much less about “action” in the abstract than Hamlet does, and are therefore less troubled about the possibility of acting effectively. They simply act as they feel is appropriate. But in some sense they prove that Hamlet is right, because all of their actions miscarry. Claudius possesses himself of queen and crown through bold action, but his conscience torments him, and he is beset by threats to his authority (and, of course, he dies). Laertes resolves that nothing will distract him from acting out his revenge, but he is easily influenced and manipulated into serving Claudius’s ends, and his poisoned rapier is turned back upon himself.
In the aftermath of his father’s murder, Hamlet is obsessed with the idea of death, and over the course of the play he considers death from a great many perspectives. He ponders both the spiritual aftermath of death, embodied in the ghost, and the physical remainders of the dead, such as by Yorick’s skull and the decaying corpses in the cemetery. Throughout, the idea of death is closely tied to the themes of spirituality, truth, and uncertainty in that death may bring the answers to Hamlet’s deepest questions, ending once and for all the problem of trying to determine truth in an ambiguous world. And, since death is both the cause and the consequence of revenge, it is intimately tied to the theme of revenge and justice—Claudius’s murder of King Hamlet initiates Hamlet’s quest for revenge, and Claudius’s death is the end of that quest.
The question of his own death plagues Hamlet as well, as he repeatedly contemplates whether or not suicide is a morally legitimate action in an unbearably painful world. Hamlet’s grief and misery is such that he frequently longs for death to end his suffering, but he fears that if he commits suicide, he will be consigned to eternal suffering in hell because of the Christian religion’s prohibition of suicide. In his famous “To be or not to be” soliloquy (III.i), Hamlet philosophically concludes that no one would choose to endure the pain of life if he or she were not afraid of what will come after death, and that it is this fear which causes complex moral considerations to interfere with the capacity for action.
Everything is connected in Hamlet, including the welfare of the royal family and the health of the state as a whole. The play’s early scenes explore the sense of anxiety and dread that surrounds the transfer of power from one ruler to the next. Throughout the play, characters draw explicit connections between the moral legitimacy of a ruler and the health of the nation. Denmark is frequently described as a physical body made ill by the moral corruption of Claudius and Gertrude, and many observers interpret the presence of the ghost as a supernatural omen indicating that “[s]omething is rotten in the state of Denmark” (I.iv.67). The dead King Hamlet is portrayed as a strong, forthright ruler under whose guard the state was in good health, while Claudius, a wicked politician, has corrupted and compromised Denmark to satisfy his own appetites. At the end of the play, the rise to power of the upright Fortinbras suggests that Denmark will be strengthened once again.