What are the delusions (madness) of Willy Loman in Death of a Salesman by Arthur Miller?

One of Willy's major delusions in Death of a
Salesman is his conjuring of Ben.  Whenever Willy begins to think about his
dreams, he imagines talking to Ben about making it big.  The audience knows that Ben
died long ago; however, Willy constructs Ben's persona as if he were alive and well. 
Willy's hallucinations go much farther than simply remembering times past with Ben--he
imagines that he tells Ben about all that is going on in the present.  Therefore, Ben
represents a form of Willy's madness.  In the play, Willy's madness is created by his
illusions of what he believes is the American Dream, so his delusions are all rooted in
Willy's irrational efforts to achieve "the dream."