#7

I believe that Hamlet's "antic disposition" is both of surprise and self interest. Of course Hamlet is astounded at the sight of his fathers ghost, but he does see the use of the ghost to his advantage. By appearing to have gone crazy, he has won a specific perspective from his friends upon himself and can use that to construct his next move. In other words, if he knows the king is thinking one way, that he is indeed mad, then he can shape his approach to his murder, play etc. the way he chooses without fear of being discovered.