Hamlet's belief in the devil thesis

Thomas Alfred Spalding speculates, in his Elizabethan Demonology, that within the context of the time, Hamlet must have entertained the notion that the ghost that appears to him was diabolical.

...he [Hamlet] declares most forcibly that he believes the devil theory possible, and consequently that the dead do not return to this world; and his utterances in his soliloquy are only an accentuation and outcome of this feeling of uncertainty. The very root of his desire for death is that he cannot discard with any feeling of certitude the Protestant doctrine that no traveler does after death return from the invisible world, and that the so-called ghosts are a diabolic deception.  --T.A. Spalding, p. 61.

Such an interpretation offers a vision of Hamlet that is quite different than the one we have seen on our stages for the past two hundred years. In it, Hamlet is confronted with an incarnation of evil itself at the beginning of the play, and despite his own internal resistance, yields to its force by the end of the play. In effect, the trajectory of the play is such that while resisting the evil that he has been called to, he falls into it, and, in his decline, ends up wallowing in evil as the corpses pile up. While such an interpretation is consistent with the understanding of ghosts and walking spirits documented in this section, it is given further support by the Elizabethan concern with revenge which is documented in the next.