What are Iago's motives in Othello?

Iago works against and tries to ruin Othello, Desdemona, and Cassio in the play and the chief aim of his life is to destroy the happiness of all these three honest and innocent people. He is eminently successful in the plans and schemes which he engineers against these three victims. The question that naturally rises is: what are the motives of Iago’s actions and schemes against his enemies? Apparently and so far as all outward appearances are concerned; Iago has certain definite and well-defined motives for the action which he undertakes against Cassio and Othello.

           The main cause of complaint and grudge which Iago has against Othello is that instead of appointing him as his lieutenant, he has chosen Cassio for this post, and has given to him (Iago) the humiliating and low rank of the ensign or the ancient or the standard-bearer. The appointment of Cassio as lieutenant in preference to his own valiant self-gnaws deep into the heart of Iago and makes him angry with the Moor because he has chosen a mere arithmetician, a debtor and creditor, and a counter-caster i.e. Cassio, as his lieutenant and has ignored his claims, when he knows that Michael Cassio:

“Never set a squadron in the field,

Nor the devision of a battle knows,

More than a spinster”,

               Iago is incensed because the Moor who had seen him fighting on the battlefield at ‘Rhodes, at Cyprus and on other grounds, Christian and heathen’, should completely ignore him and give the post of the lieutenant to Cassio who was not half so brave and experienced in military matters as Iago was. Another reason for Iago’s hatred for the Moor is that he (Othello, the Moor) has established illicit relation with his (Iago’s) wife:

 “I hate the Moor,

And it is thought abroad, that ‘twixt my sheets

He’s done my office; I know not if ‘t be true…

Yet I, for mere suspicion in that kind,

Will do, as if for surety, he holds me well

The better shall my purpose work on him”.

             Iago intends to take revenge against Othello and he desires to be “even’d with him, wife for wife”. So far as Cassio is concerned, Iago has the suspicion of illegitimate sexual relationship between the lieutenant and his (Iago’s) wife. He says:

 “For I fear Cassio with my night-cap, too--”

                  Iago is infuriated against Cassio primarily because of his appointment as lieutenant and secondly because he thinks that he (Cassio) has illicit sexual relations with his (Iago’s) wife. Actuated by these motives, he seeks to bring about the ruin of these people. But these motives are considered too feeble by critics, for the kind of action that Iago actually takes against his victims.

In Iago’s soliloquy, he (Iago) gives us the above stated motives of action against Othello and Cassio, but, in fact, they are not his true motives. He is simply trying to hunt motives in order to justify his malignity against virtuous and innocent people. As Dr. A.C. Bradley points out, “Iago did not clearly understand what was moving his desire, though he tried to give himself reasons for his actions, even those that had some reality made but a small part of the motive force”. Brandes is of the opinion that Iago’s apparent motives of action against Othello and Cassio are not his real motives. His real motives lie elsewhere and are deeply rooted in his inherent malignity and evil mindedness.