Othello the protagonist of the play is the first and most important victim of the psychological manipulation by Iago, who slowly and carefully puts the infectious and poisonous doubt about Desdemona's moral character. Iago manages the conspiracy so cleverly: he makes Cassio drink and behave irresponsibly so that Othello dismisses Cassio.
Then he tells Cassio to go and plead Desdemona for his lost job; but he brings Othello at a moment when poor Cassio steals out 'guilty-like'. This had already had some effect on Othello's mind. To this, Iago adds many kinds of doubts and comments, and finally gives him certain 'evidence' by making them up instantly and cleverly. Othello loses his common sense, and an open and critical mind; he is blinded by the jealousy and anger against his wife. He becomes a psychologically imbalanced kind of person; he believes whatever the false and dangerous villain says and he doubts whatever his wife says. Then he madly rushes into the disgusting action of killing his innocent wife.
The other characters like Desdemona, Cassio and Roderigo are also all victims of lago's psychological manipulation. They are all mentally weak. Desdemona is too innocent and ignorant to doubt her husband who has begun to think of her as a 'whore’! She can't believe her ears, even when he openly calls her a 'whore'. Her blind love for Othello is the cause of such madness. Roderigo is a victim due to his irrational hope for Desdemona, even when he knows that she is a very loving wife of someone. Cassio is also duped because he is blinded by the hope of his lost job. He is a simpleton like Roderigo and Desdemona. In this way, the theme of psychological manipulation is maintained by raising the issues of gullibility, jealousy, lack of critical outlook, and the blinding passions of love or hope
The Theme of Jealousy
In a sense, Shakespeare's domestic play Othello is a play about sexual jealousy; the main tragic character Othello brings about his own disaster due to jealousy, and two other male characters are also somehow the victims of jealousy and self-consuming revenge. Othello is a great and wise man, except for his blindness of thought and the rashness of action caused by his sexual jealousy. He never pauses to think what the reality of anything may be, once he is blinded and maddened by a small seed of jealousy. Othello becomes so angry when he sees a very, very small possibility of Cassio's infidelity. No other sane man in the world would doubt his innocent wife so easily; we never see any other smallest bit of the reason that Desdemona was or is possibly untrue to her wedlock. But we also understand that Othello would not be so mad and blind as to believe whatever Iago says, if it was not related to sexual matters. He would never believe a lie in his military field! Once it comes to the point of harm against his marital bliss, he loses all power to look beneath the surface. Poor man, he does make some feeble effort to disbelieve the villain, but his irrational mind rules him as soon as it touches his hypersensitive mind about his love and marriage. He is too loving and therefore too unloving when pricked by doubt and a possible betrayal. He becomes hateful because of a blind jealousy that suspends and exterminates all his goodness and happiness.
In a limited sense, Roderigo and Iago are also involved in some sort of jealousy. Roderigo is jealous of Othello's marriage with Desdemona and he is blinded by his obsessive passion for beautiful Desdemona. But, by far the most important motivation in the drama is Othello's jealousy against the innocent Cassio. It is Othello's jealousy that complicates and develops the plot of the play, and it is his jealousy that brings about the catastrophe and tragedy in the life of the otherwise heroic Othello.
Othello's Gullibility
Othello's first identity is his gullibility. He is the protagonist of the play and is a complex, round character; but he is so pig-headed that once he is thrust towards a belief or doubt, he leads it to its extreme. He is tough, determined and committed to justice and righteousness. The tale of Othello's bygone days is an enchanting romance through which beautiful Desdemona easily falls in love with him. He is also a public figure, the commander of Venetian army and the pillar of security for the state of Venice. The fall of so much nobility embodied in him is really shocking but convincing if every step of Othello's disposition is taken into account. Othello is ruined because he is gullible. Indeed, Othello changes much for the worse in play revealing himself weak in mind and weak in heart. His gullibility is 'the hamartia, his tragic weakness.
Appearance versus Reality
Many characters appear the opposite of what they actually are, and the entire situation is also wrongly evaluated by the tragic hero. The best example of false character is Iago, We know him as a scheming rogue, but all the characters in the play, including his own wife, are deceived by his false appearance until the end. Desdemona is so chaste and loving and good, but she appears dirty to her husband. So is the case with the loyal Cassio. Even the minor character Brabantio is deceived by the appearance: he never knows how his ignorant and immature daughter prepares to elope with a black man. This theme of appearance and reality is best indicated in lago's description of his own personality: "I am not what I am", and when he teases Othello with an irony: "Men must be what they seem to be".
Service versus Betrayal
This theme is manifest in the contrast between Cassio and Iago. Cassio, who has always given loyal and responsible service to his general Othello gets hatred and violence in return; but silly Othello rewards the terribly evil lago with love and trust in return to his betrayal. The grateful and humble gets an injury, whereas the thankful and malicious gets respect. That irony is the cause of so much tension to the audience, and is also one of the thematic issues of the play.
Love versus Hatred
Desdemona blindly and sincerely loves Othello, but she gets hatred and humiliation in return. The same is the case of Cassio; his love for the couple of Desdemona and Othello is like that of a humble servant sincerely loving his masters, or that of an obedient brother loving his brother and sister-in-law. But he is also victimized by an unjustified, but terrible hatred. True love, that between Othello and Desdemona, is destroyed by blind jealousy; the love among other people is only false. lago's love for Roderigo and everybody else, including his own wife is false and devilishly deceptive. So the hatred dominates and destroys love in the drama.
Healthy Reasoning versus Blind Emotions
Othello's power of healthy and open-minded thinking is quickly destroyed by hatred, jealousy and revenge. It is the lack of sound reasoning and a critical mind that brings about all the disaster and, misery in the life of Othello, and even in the lives of other characters like Desdemona and Cassio. Desdemona lacks the power of critical thinking. Otherwise, she would have at least understood that Othello is jealous, and that it was good for her not to talk about any man in his mood of mad anger. Her foolish attempt to press the case of Cassio and her blindness towards the evil of the world is due to the blind passion of love for her husband. Roderigo is also another victim of the same type of blind hope, like Cassio, who is also destroyed by hopeless hopes that make him lose common sense and patient reasoning.
Dignity versus Malignity
Othello, the hero of the play, is a dignified (respected) personality as we see him in the beginning of the play. He is not only the general of the army of Venice he is so important that the government depends on his power and efficiency to protect their new-gained province of Cyprus. This dignity of Othello is such an advantage that the Duke trusts him as having genuinely persuaded Desdemona rather than charmed her with magic. On top of that, he jokes by saying that even his own daughter would fall in love when the brave young soldier told those stories of adventure and challenge. But, this dignity of the hero collapses into nothing very soon. When the seed of jealousy is sown in his mind, it begins to grow like moss in the sea. It overpowers his rational mind and blinds his reasoning. He becomes so mad with malignity (the desire to do harm to others) towards his wife and his assistant Cassio that he forgets to have any second thought about what might be the reality. The great Othello becomes a mean murderer of his wonderful wife. He becomes a disgusting villain if we think of how aggressive, arrogant and insane he is. That is the theme of dignity, turning into malignity. It is Iago the poisonous snake who turns all well into such evil as murderous malice.
Chastity versus Adultery
Desdemona is chaste, but she is charged with adultery. The issue of adultery comes up in the talk between Desdemona and Emilia before Desdemona is murdered by her husband. Desdemona can't even tolerate the thought of it, whereas Emilia suggests that she would take revenge of an immoral husband by involving herself in adultery! In this seventeenth century play, the issue of women's chastity becomes so serious, and indeed it is a serious matter. But the problem is that men do not seem to bother about their own purity! This is the reflection of the attitude of the people of the time, including the dramatist himself.