One dominant theme in Shakespeare's Othello is the illusion of appearances, or even deception. In the very first scene, we see some very poignant literary devices in Iago's speeches when he is explaining to Roderigo exactly why he hates Othello and trying to enlist Roderigo's assistance in revenge; these literary devices serve to underscore the theme of appearances.
One device is the metaphor Iago uses in saying it is not long that he "will wear [his] heart upon [his] sleeve for daws [crows] to peck at" (66-68). Here, Iago is saying that in a very short time, he will stop showering Othello with the praises and loyalty that Iago's own post commands, because Iago will soon enact his revenge. Interestingly, as we progress through the play, we soon see that Iago is not the only character who is falsely wearing his heart on his sleeve. Othello also proves to be wearing his heart on his sleeve as he showers Desdemona with affection. But, just like Iago, it's not long before Othello stops showering Desdemona with affection, showing just how much of an illusion his love truly is.
A second poignant literary device can be seen in Iago's final statement in this speech: "I am not what I am" (68). This sentence is a form of parallelism called antithesis, and both parallelism and antitheses are considered rhetorical devices. Parallelism is simply when authors create patterns using grammar and sentence structure; such patterns can create dramatic emphasis. There are many different types of parallel structures. Antithesis specifically happens when a writer reveals "contrary ideas" in a "balanced sentence" (Dr. Wheeler, "Schemes"). Dr. Wheeler gives us the example, "One small step for a man, one giant leap for all mankind" ("Schemes"). In Iago's sentence, we can clearly see how the ideas "I am" and "not what I am" contrast, making the sentence an excellent example of antithesis. What's more, the use of antithesis helps to dramatically emphasize the fact that Iago is not all he is presently showing himself to be, which underscores the theme of the illusion of appearances.