Also, the sheer numbers of excuses that Iago gives are proof of his ulterior motives. He seems to conveniently add new reasons for his hate every time he needs to encourage Roderigo to do something for him. He first announces that he wants to get revenge on Othello and Cassio
because Iago was passed up for the promotion. Then, he adds that he has reason to believe that Othello may have slept with Emilia, Iago’s wife. After Cassio has been demoted he goes on to say that Cassio must be killed since he is too good looking. His supposed motives look solid on
the surface, but turn out to be quite flimsy and based on unreliable sources. Even so, one, even two, of these excuses would be more plausible than the ever-changing answers that Iago gives as reasons for his hatred.