THE GHOST AND THE KING

The Ghost is referred to by the characters as the shadow or the likeness of the king.  But Hamlet recognizes that despite its outward appearance, the apparition may not necessarily be the king.  For example, it could be a demon tempting him to kill Claudius on false pretenses.   



Of course, Hamlet is using this possibility as a justification for his inaction.

"The body is with the king but the king is not with the body."  IV.ii.   Hamlet says this in reference to Claudius, but it also alludes to the ghost of his dead father.