to make cassio mad to he can get in a fight with him because cassio has a hot temper
so iago tell this to roderigo to Othello could release Cassio of his position as lieutenant .
Iago gets Cassio drunk in the night so after he is drunk Roderigo comes out and makes Cassio angry again so they get in a fight during they fighting some one goes and ring the bell to Othello could be awerd so Otello comes out of his room and he ask whtas going on so Montano tells him and Othello said that even thouhg as much he loves him he has to discharged him out of his position of lieutenant .
Primarily the fact that Iago has suggested to him that that is what is being talked about. By this point, Iago has got Othello into such a state he cannot interpret anything Cassio or Desdemona does as being innocent.
Iago wanted Cassio to drink more wine because he wanted Cassio to be drunk and argumentative when Roderigo would approach him later that night. Iago told Montano that Cassio was drunk every night. He wanted to cast doubt on Othello's judgment for appointing Cassio, by implying that Cassio may be drunk during battle. This led to Othello stripping Cassio of his position. Othello thought that Cassio was irresponsible and dishonourable.
Bianca
Othello commits suicide. Iago is sentenced to torture. Cassio becomes governor of Cyprus.
Iago had lied to Othello and convinced him that Desdemona was secretly having sex with Cassio.
Iago advises Cassio to ask Desdemona to plead on his behalf. This will help Iago poison Othello's mind, as Desdemona will appear to be doing so out of her (illicit) love for Cassio.
The advice that overwhelmed Othello was to kill Desdemona and he will take care of Cassio
Iago feels that Cassio's promotion should have gone to him. He envies Cassio.
Iago says that he was sleeping next to Cassio and that Cassio was having a dream about making love to Desdemona.
He tells him that the best way for him to get his place back is to get Desdemona to plead with Othello, which would probably be good advice if Iago had not at the same time suggested to Othello that Desdemona was having an affair with Cassio. Because of Iago's suggestion, Desdemona's concern for Cassio looks like confirmation of her having an affair with him.
Othello was just out of earshot when Iago talks to Cassio. He has told Othello that he is talking to Cassio about Desdemona but he is really talking about the woman that Cassio is really having an affair with, Bianca. In 'Othello' Iago tricks Othello by planting Desdemona's handkerchief in Cassio's room.
Iago has been passed over for a promotion. Cassio got the promotion to Lieutenant even though Iago had more time in service as a soldier. Cassio got the promotion over Iago because his learning included theory and strategy whereas Iago's did not.
Othello said that Iago is such a loyal friend to Cassio that Iago told about the fight in a way that looked better on Cassio. Even so, Othello fires Cassio and understands that Iago did what any friend would do.
It would make it seem that Iago did his part in the plan, where Iago kills Cassio and Othello kills Desdemona. Even though Iago got Roderigo to do it for him.
Lieutenant.
Iago's plan is to make Cassio drunk and get him into a brawl that will ruin Cassio's reputation and cause him to lose his position. He urges Roderigo to provoke Cassio "to put our Cassio in some action/ that may offend the isle." As usual,Roderigo is duped by Iago's manipulative words and agrees to do this, even though all he ends up with is a sound beating from Cassio. Iago, however, succeeds in getting Cassio dismissed from his lieutenancy to Othello, which plays in toIago's master plan to ruin Othello.
He says that Othello placed Cassio as his lieutenant instead of him.