Iago makes Othello believe that Desdemona is cheating on Othello with Cassio because when Cassio goes to Desdemona for help Iago words the situation to Othello in a way where he would believe that Desdemona was being unfaithful to him with Cassio. When Cassio went to talk to Desdemona Iago notices that Cassio holds Desdemona’s hand as he talks to her, so once Iago realized this was when he made the plan to make it seem as if Cassio has a liking for Desdemona. Iago makes Othello believe that Desdemona is is not as pure as she appears to be. By doing this he causes Othello to become upset with Desdemona and Cassio.
The next step Iago takes to manipulate Othello is when he steals the handkerchief that Othello gave Desdemona from her and plants it on Cassio. Iago manages to get the handkerchief because when Desdemona tried to offer it to Othello while they were at dinner Othello pushed her away and she dropped it. Iago then retrieves the lost handkerchief from Emilia and uses it to convince Othello, along with his other false stories, that Desdemona is an unfaithful wife. Once Iago gets Othello to see that his wife does not have the handkerchief but Cassio does, he begins to believe Iago’s lies, and that makes Othello even more angry towards them. Now that Iago has Othello begun to believe Iago’s stories even more, that helps Iago’s plan to make Othello turn against his wife and Cassio. Iago realizes that his plan is working, so he continues to lie to Othello.
Lastly, Iago arranges for Othello to overhear a conversation between himself and Cassio so that Othello believes he is hearing a confession. Iago tells Othello that he will talk to Cassio and ask him about his sexual relations with Desdemona, allowing Othello to listen to the conversation. Instead, when Cassio comes to talk Iago asks him about Bianca, not Desdemona. By doing this Iago is making his plan easier for Othello to believe. This upsets Othello even further because he believes that he is hearing all the details from Cassio’s and Desdemona’s affair not Cassio’s and Bianca’s. The purpose of Iago making up these false stories is to make Othello upset with Cassio and Desdemona. His greatest intention was for Othello to be upset with Cassio. Iago wanted this because Othello gave the job of lieutenant to Cassio instead of more than him. When Othello did this it upset Iago greatly because he believed that he deserved the job over Cassio because he had more battle experience than Cassio, but Iago didn’t realize that Othello gave the job to Cassio because he had more book knowledge than him. Iago stole the handkerchief from Desdemona because he knew how much it meant to Othello, and the fact that she didn’t have it but Cassio did made him the most upset because that handkerchief is very important to Othello. In the end Othello vows to attain vengeance against Cassio and Desdemona. Iago does this by first, lying to Othello and making him believe that Desdemona is cheating on Othello with Cassio. The next step Iago takes to manipulate Othello is when he steals the handkerchief that Othello gave Desdemona, from Desdemona and plants it on Cassio. Finally, Iago arranges for Othello to overhear a conversation between himself and Cassio so that Othello believes he is hearing a confession. Iago ends up manipulating Othello to the point where he kills his wife and himself as well, because Othello gives in to his fears and his natural jealousy.
Shakespeare, William. The_Arden_Shakespeare_Complete_Work. Thomas Nelson and Sons LTD; 1998.