In an effort to win Othello’s good graces, Cassio sends musicians to play music beneath the general’s window. Othello sends his servant, a clown, or peasant, to tell the musicians to go away. Cassio asks the clown to entreat Emilia to come speak with him, so that he can ask her for access to Desdemona. When the clown leaves, Iago enters and tells Cassio that he will send for Emilia straightaway and figure out a way to take Othello aside so that Cassio and Desdemona can confer privately. After Iago exits, Emilia enters and tells Cassio that Othello and Desdemona have been discussing his case. Desdemona has pleaded for Cassio, but Othello worries that Montano’s influence and popularity in Cyprus would make Cassio’s reappointment impractical, no matter how much Othello cares for his former lieutenant. Emilia allows Cassio to come in and tells him to wait for Desdemona.

Iago, Othello, and a gentleman walk together at the citadel. Othello gives Iago some letters to deliver and decides to take a look at the town’s fortification.

Desdemona, Cassio, and Emilia enter mid-conversation. Desdemona has just vowed to do everything she can on Cassio’s behalf when Othello and Iago enter. Cassio quickly departs, protesting to Desdemona that he feels too uneasy to do himself any good. Othello asks whether it was Cassio he saw leaving the room, and Iago responds that surely Cassio would not behave like a guilty man at Othello’s approach.

Desdemona entreats Othello to forgive Cassio and reinstate him as lieutenant. Othello assures her that he will speak to Cassio, but he answers evasively when she tries to set a meeting time. She criticizes Othello for responding to her request so grudgingly and hesitantly, and he tells her that he will deny her nothing but wishes to be left to himself for a little while.

Alone with Othello, Iago begins his insinuations of an affair between Cassio and Desdemona by reminding Othello that Cassio served as Othello and Desdemona’s go-between during their courtship. Othello asks Iago whether he believes Cassio to be honest, and Iago feigns reluctance to answer. Iago plants in Othello’s mind thoughts of adultery, cuckoldry, and hypocrisy, until Othello screams at the ensign to speak his mind. Iago suggests that Othello observe his wife closely when she is with Cassio.

Othello tells Iago to have Emilia watch Desdemona when she is with Cassio. Iago appears to retreat from his accusations and suggests that Othello leave the matter alone. But he has already made his point. By himself, Othello muses that his wife no longer loves him, probably because he is too old for her, because he is black, and because he doesn’t have the manners of a courtier. “She’s gone,” he laments (III.iii.271).

Desdemona and Emilia enter to inform Othello that he is expected at dinner. Othello says that he has a pain in his forehead, and Desdemona offers to bind his head with her handkerchief. Othello pushes her handkerchief away, telling her that it is too small. The handkerchief drops to the floor, where it remains as Othello and Desdemona exit. Emilia, staying behind, picks up the handkerchief, remarking that her husband has asked her to steal it at least a hundred times. Iago enters, and Emilia teases him with the promise of a surprise. He is ecstatic when she gives it to him, and sends her away.

As Iago gleefully plots to plant the handkerchief in Cassio’s room, Othello enters and flies into a rage at him. Othello declares that his soul is in torment, and that it would be better to be deceived completely than to suspect without proof. He demands that Iago bring him visual evidence that Desdemona is a whore. Iago protests that it would be impossible to actually witness Desdemona and Cassio having sex, even if the two were as lustful as animals. He promises that he can provide circumstantial evidence, however. First, he tells Othello that while Cassio and Iago were sharing a bed, Cassio called out Desdemona’s name in his sleep, wrung Iago’s hand, kissed him hard on the lips, and threw his leg over Iago’s thigh. This story enrages Othello, and Iago reminds him that it was only Cassio’s dream. Iago then claims to have witnessed Cassio wiping his beard with the handkerchief Othello gave Desdemona as her first gift. Furious, Othello cries out for blood. He kneels and vows to heaven that he will take his revenge on Desdemona and Cassio, and Iago kneels with him, vowing to help execute his master’s vengeance. Othello promotes Iago to lieutenant.

The timing of events is very important in Act III. Iago anticipates and manipulates the other characters so skillfully that they seem to be acting simultaneously of their own free will and as Iago’s puppets. For example, it takes only the slightest prompting on Iago’s part to put Othello into the proper frame of mind to be consumed by jealousy—Iago exploits Cassio’s discomfort upon seeing Othello by interpreting it as a sign of guilt. Iago’s interpretation of Cassio’s exit, combined with Desdemona’s vigorous advocating on Cassio’s behalf, creates suspicion in Othello’s mind even before Iago prompts Othello. Othello manifests his confusion about his wife by telling her that he wishes to be left alone, and by spurning her offer of help when he tells her that he feels unwell.

When Desdemona advocates on Cassio’s behalf, she initiates the first real onstage conversation she has had with her husband throughout the play. She also displays her strong, generous, and independent personality. In addition to his burgeoning suspicion, Othello’s moodiness may also result from his dislike of Desdemona herself. Only once Desdemona has left does Othello recover somewhat: “Excellent wretch!” he says affectionately. “Perdition catch my soul / But I do love thee, and when I love thee not, / Chaos is come again” (III.iii.91–93). Othello seems far more comfortable expressing his love for Desdemona when she is absent. Perhaps this is because her presence makes him conscious of her claim upon him and of his obligation to honor her requests, or perhaps this is because he is more in love with some idea or image of Desdemona than he is with Desdemona herself. The lines just quoted indicate how much his image of her means to him: if he stops loving her, the entire universe stops making sense for him, and the world is reduced to “Chaos.”

Given how much is at stake for Othello in his idea of Desdemona, it is remarkable how he becomes completely consumed by jealousy in such a short time. Moreover, it takes very little evidence to convince him of her unfaithfulness. All Iago has to do to Othello is make him doubt Desdemona, and jealousy spreads like a virus until he rejects her absolutely. Notably, Iago, too, has no evidence that Othello has slept with Emilia, but the suspicion or doubt seems to have been sufficient to make him spurn Emilia and persecute Othello. As Othello says, “[T]o be once in doubt / Is once to be resolved” (III.iii.183–184).

Othello soon learns, however, that to be once in doubt is to be never resolved. He leaves the stage briefly after the episode in which he rejects Desdemona’s handkerchief, at which point he seems resolved that his wife no longer loves him. A mere forty lines later, he returns, and all he can think about is garnering proof of her infidelity. The paradox in Othello’s situation is that there are few things—the nature of friends, enemies, and wives included—that a human being can know with certainty. Most relationships must be accepted based on faith or trust, a quality that Othello is unwilling to extend to his own wife. All Iago really has to do to provoke Othello is to remind him that he doesn’t know for certain what his wife is doing or feeling. Iago’s advice that Othello “[l]ook to [his] wife. Observe her well. . . .” appears harmless at first, until one considers how out of the ordinary it is for a husband to “observe” his wife as if she were a specimen under a microscope (III.iii.201). For a man to treat his wife as a problem to be solved or a thing to be known, rather than as a person with a claim upon him, is simply incompatible with the day-to-day business of being married. Othello’s rejection of his wife’s offering of physical solace (via the handkerchief), and his termination of the exchange in which Desdemona argues for Cassio, thereby asserting a marital right, clearly demonstrate this incompatibility.

Ironically, Iago doesn’t have to prove his own fidelity to Othello for Othello to take everything Iago suggests on faith. On the contrary, Othello actually infers that Iago holds back more damning knowledge of Desdemona’s offenses out of his great love for Othello. Again and again, Iago insists that he speaks out only because of this love. His claim, “My lord, you know I love you” (III.iii.121) even echoes Peter’s insistent words to Christ, “Lord, thou knowest that I love thee” (John 21:15–17).

Othello’s rejection of Desdemona’s offer of her handkerchief is an emphatic rejection of Desdemona herself. He tells her he has a pain “upon” his forehead and dismisses her handkerchief as “too little” to bind his head with, implying that invisible horns are growing out of his head. Horns are the traditional symbol of the cuckold, a husband whose wife is unfaithful to him. Othello’s indirect allusion to these horns suggests that the thought of being a cuckold causes him pain but that he is not willing to confront his wife directly with his suspicions.

The end of Act III, scene iii, is the climax of Othello. Convinced of his wife’s corruption, Othello makes a sacred oath never to change his mind about her or to soften his feelings toward her until he enacts a violent revenge. At this point, Othello is fixed in his course, and the disastrous ending of the play is unavoidable. Othello engages Iago in a perverse marriage ceremony, in which each kneels and solemnly pledges to the other to take vengeance on Desdemona and Cassio. Just as the play replaces the security of peace with the anxiety of domestic strife, Othello replaces the security of his marriage with the hateful paranoia of an alliance with Iago. Iago’s final words in this scene chillingly mock the language of love and marriage: “I am your own forever” (III.iii.482).