Alongside Hamlets major themes, like death, revenge and Hamlets inability to act, a number of sub-themes emerge in the play:
The State of Denmark
The political and social condition of Denmark is referred to throughout the play and the ghost is an embodiment of Denmarks growing social unrest. This is because the blood-line of the monarchy has been unnaturally disrupted by Claudius, an immoral and power-hungry king.
At the time this play was written, Queen Elizabeth was 60 and there was concern about who would inherit the throne. Mary Queen of Scots son was an heir, but had the potential to ignite the political tension between Britain and Scotland. Therefore, the state of Denmark in Hamlet could be a reflection of Britains own social unrest.
Sexuality and Incest
Gertrudes incestuous relationship with her bother-in-law plagues Hamlet more that his fathers death. In Act 3, Scene 4, he accuses his mother of living In the rank sweat of an enseamed bed, / Stewed in corruption, honeying and making love / Over the nasty sty.
Gertrude has destroyed Hamlets faith in women, which is perhaps why his feelings towards Ophelia become ambivalent.
Yet, Hamlet is not so angered by his uncles incest it is Gertrude, not Claudius that he blames. Perhaps the reason for this is a combination of womens passive role in society and Hamlets overpowering (maybe even verging on incestuous) passion for his mother.
Ophelias sexuality is also controlled by the men in her life. Laertes and Polonius are overbearing guardians and insist that she rejects Hamlets advances, despite her love for him.
Uncertainty
In Hamlet, Shakespeare uses uncertainty more like a dramatic device than a theme. The uncertainties of the unfolding plot are what drive the actions of each character.
From the very beginning of the play, the ghost poses a great deal of uncertainty for Hamlet. He (and we) are uncertain about the ghosts purpose is it a sign of Denmarks socio-political instability, a manifestation of Hamlets own conscience, an evil spirit provoking him to murder, or his fathers spirit unable to rest?
Hamlets uncertainty delays him from taking action, ultimately causing the unnecessary deaths of Polonius, Laertes, Ophelia, Gertrude, Rosencrantz and Guildenstern.
Even at the end of the play, we are left with a feeling of uncertainty when Hamlet bequeaths the throne to the rash and violent Fortinbras. In the closing moments of the play, Denmarks future looks less certain than it did at the beginning.

