Give 2 examples of dramatic irony in Oedipus Rex. Explain what the audience knows and the effect that knowledge has on the reader.

Going into any reading or viewing of Oedipus
Rex, the audience would know
that:

• Oedipus has already killed his
  father


• married his mother (committed
  incest)


• fathered four children who are also his siblings
  

Oedipus is a universally known myth, and all
of the background information (or antecedent action) is common knowledge.  I don't know
if those count or not, since they have taken place before the play
begins.

During the play, we (the audience) know more than
any of the characters on stage, except for Tiresias.  The play is driven by dramatic
irony, and here are the main ironies of part I
only:

• We know the cause of the plague in Thebes:
  incest and murder


• We know Oedipus' curse on the murderer
  of Laius will lead to his banishment


• We know that
  Oedipus' search for the murderer will lead to his knowledge of his own
  crimes


• We know that Creon is telling the truth, that he's
  not a traitor


• We know that Tiresias is telling the truth,
  that Oedipus is the murderer


• We know that Jocasta will
  know the truth sooner than Oedipus, and her suicide will finally confirm the
  truth


• We know that Oedipus will gouge his eyes, an ironic
  punishment for not knowing or seeing the
  truth

The effects lead to
katharsis (purgation of pity and fear) in the audience.  We pity
Oedipus for seeking to know the truth only to have that truth backfire on him and make
him suffer.  We fear that his plight might be our own: not that we will commit his two
crimes necessarily, but that we may never know the truths about ourselves and our
families, and even when we do, it leads only to pain and
suffering.