"Othello, the Moor of Venice"

Shakespeare develops a theme of deception early on in Othello, the Moor of Venice. In Scene one of the first Act, Iago and Roderigo go to the house of Brabantio and claim he has been deceived by Othello, the captain of the Venetian army, in that he married Brabantio's daughter without his knowledge or consent.  Roderigo, obviously angered by the fact that Desdemona did not choose him, presents the idea that Brabantio may have been deceived by his own daughter.  "Your daughter, if you have not given her leave, I say again, hath made a gross revolt, Trying her duty, beauty, wit, and fortunes, In a extravagant and wheeling stranger Of here and everywhere" (Shakespeare, I.i.131-135).  At first, Brabantio does not believe he has been deceived by his own flesh and blood, rather he supposes his daughter was drugged and did not freely consent to the marriage.  When Desdemona confesses her love for Othello, then he declares "treason of the blood."  At this point in the play Brabantio and Roderigo experience deception.
In Act 2 and Act 3, Shakespeare furthers this theme through dramatic irony.  The audience is aware that Othello, Desdemona, and Cassio are all being deceived.  The most obvious display of this deception occurs when Cassio is pressured to drink and fight by Roderigo and Iago which results in Cassio's loss of position in the Venetian army.  Desdemona, too, is being deceived by Iago.  Iago is making her appear as an adulterer to the eyes of Othello who, by default, is also being deceived.  In all but one of these cases of deception (Roderigo's feeling deceived by Desdemona), the culpability lies upon but one character: Iago.