Two of the main themes in "Othello" seem to be suspicion and envy, these factors combined lead to the downfall of not only Othello but also Iago. We learn how envy appears to destroy Othello; we see how Iago brings on this envy through the deception of Othello. Shakespeare constantly emphasizes and repeats the line, "Honest Iago" it creates such a feeling of frustration in the audience. Furthermore one can see how Iago's envy grows throughout the play due to the promotion of Cassio to lieutenant.
To explore the themes fully we must look at each character and the way they act toward others.
Othello for example harbours mainly suspicion but also envy toward Cassio. Suspicion toward Cassio later on as the play develops; due to the interference of Iago in convincing him that Cassio is sleeping with his woman. Othello's nature is actually a very trusting one; take his relationship with Iago for example, he becomes suspicious through Iago's convincing theories about Desdemona and Cassio.
Othello is an example of how suspicion can corrupt a person. Through almost no concrete evidence Iago has made Othello kill his own wife; because of envy, Iago's envy. In the beginning of the text, Iago is known as "honest Iago", however, throughout the play, he constantly lies and schemes plans to get at Othello. One cannot entirely blame Iago for Othello's doings. Othello never really questions Iago, he accepts it as if expecting it, his constant suspicions blind him to what Iago is really doing.
Othello's envious state at the point when Iago speaks of Cassio and Desdemona together we really see Othello opened up, he is enraged with envy and jealousy,
"Lie with her? Lie on her?
We say lie on her when they belie her.
Lie with her! Zounds, that's fulsome.