Show how good versus evil, how they have power over the other.

Iago's battle against Othello and Cassio certainly counts as an embodiment of this theme. Iago and his evil battle to corrupt and turn the flawed natures of other characters, and he does succeed to some extent. By the end of the play, neither has won, as Desdemona and Emilia are both dead, and Iago revealed and punished. Othello is a tragic character, but one that is neither good nor evil. His flaws are easily manipulated, and he is unable to see the truth while blinded by pride. He is a good soldier and a good man, but this good is twisted and he commits an evil act.

Desdemona is the embodiment of goodness in the play, as she has done no wrong and seeks only to love and to help her friends. However, she resigns herself to her death out of this goodness. The ruin of innocence is a key ingredient to tragedy, but one could interpret that Desdemona did not have to suffer her fate. Othello represents a grey area between good and evil, where self-interest clouds even the best intentions, and people on both sides end up dead.