Both scenes 1 and 2 in Act 3 are very brief, and do not give us any insight into shifts in feelings. Scene 3 is crucial, however, because it is the pivotal scene where Iago convinces Othello that both his wife and Cassio have committed adultery. At the end of the scene, Othello decides to take revenge by murdering them both with Iago's help. Iago is also promoted to lieutenant and pledges his loyalty to Othello.
Iago is the key character in this Act, as it is he who is responsible for the shift in Othello's feelings towards Desdemona. From the beginning of the scene, he immediately plants suspicion in Othello's mind when Cassio leaves because he is still too ashamed to see Othello. Iago suggests that his motives for talking to Desdemona have been less than innocent: 'Ha, I like not that' and 'Cassio my lord?...No, I cannot think it,/ That he would sneak away so guilty-like,/ Seeing you coming'.
Othello's doubt is immediately shown through the language he uses: 'I do believe 'twas he'. These short questions and riddled speeches by Othello show that Othello is not the assertive general and eloquent lover he once was.
Language is extremely important in this scene, as it is Iago's tool in manipulating Othello. The corruption of language corrupts Othello's perception. The key word, 'honest', is used fourteen times in scene 3 alone. It is ironic that Othello expects the truth from 'honest' Iago, and that Othello's proof for his own judgement is Iago's honesty. Not only does Othello surrender his judgement to Iago, but as seeing is believing (proof), his 'sight' is also surrendered to Iago by the end of the scene. It is the proof, which he gains through Iago, which leads...