Discuss the dramatic irony in "Macbeth".

In Macbeth, Shakespeare undercuts
much of the dramatic irony in the play through the use of equivocal language by the
witches and the Porter and by combining the roles of hero and villain into one
character, Macbeth.

In this way, we as audience do no know
much more than Macbeth regarding the validity of the prophecies.  We know Macbeth is a
villain, but we don't know for sure who is good and, therefore, his nemesis.  The play
is so devoid of goodness that we don't trust anyone (the witches, Malcolm).  We even
have doubts about Macduff, who leaves his family to
slaughter.

Granted, we are not as hopeful as Macbeth
regarding the prophecies, and we know this is a tragedy and that Macbeth will not
survive, but--in a way--we still root for him to defy the odds and fate.  We want a lone
individual with courage to succeed.  This drains much of the dramatic irony out of the
play.

About the only examples of dramatic irony regard
murder and madness.  The play is quite the opposite of a detective story,
for:

1) We know the Macbeths plan to kill
Duncan

2) We know Macbeth plans to kill
Banquo

3) We know Macbeth will kill Macduff's
family

4) We see signs of Lady Macbeth's
madness

5) We know Hecate and the Witches have it in for
Macbeth

Still, there is detective work to be done regarding
the second set of prophecies.  But, we cannot expect to know that riddles that will play
out in Act V: that Macduff's mother died before delivery; that the soldiers would use
wood as a disguise; that Macbeth will be beheaded.  We are in the same position as
Macbeth regarding these events.