Iago's soliloquies and asides, in contrast to his speeches in the presence of other characters, reveals quite clearly his deceitfulness and self-disguise. The audience is not duped for a moment, as, through dramatic irony and our privileged position, we come see that he is engaged in "double-knavery" (1.2.318), and not at all the "honest and true" Iago that others believe him to be. The audience would be amazed at the absolute faith that the character have in Iago's honesty, which we know to be a lie even from his first appearance onstage.
Iago's aim throughout the play is to "blacken" Othello's reputation to match the latter's face, in revenge for what he sees as a slight in Othello's appointing Cassio lieutenant over him. In his first soliloquy in Act I, scene iii, he gives three motives for his plotting: to fatten his purse (1.2.308), "to get [Cassio's] place" as lieutenant (1.2.318), and to make "sport" on Othello whom he hates (1.2.311). He later admits that he is somewhat in love with Desdemona, and reiterates his suspicion that "the lusty Moor/ Hath leap'd into [his] seat; the thought whereof/Doth gnaw at [his] inwards" (2.1.310-14), and that one of his motives is to be avenged "wife for wife" (2.1.315).
Jealousy, susJealousy, suspicion and envy are not only key motives to Iago's actions, but are key elements of his character, as his soliloquies reveal. Not only does he harbor unfounded suspicions that Othello "hath done office 'twixt [his] sheets" (1.2.312-313), he suggests that Cassio also is likely to cuckold him (2.2.320). He gives a further reason for his jealousy of Cassio, who "hath a daily beauty in his life/That makes [him, Iago] ugly" (5.1.19-20). It is not surprising then, that the method he employs to embroil Othello in jealousy is based on the working of his own suspicious mind, where "mere suspicion /Will do as if for surety" (1.2.314-15).
On the other hand, his soliloquies reveal that he is an astute observer of character. He knows people's nature well, and thus is able to use their weaknesses and foibles to his advantage. For example, he shows keen insight into the relationship between Othello and Desdemona, in particular the latter's influence on her husband. As a result, he plans to manipulate Desdemona's liberal tongue and goodness to "enmesh them all" (2.3.366) and "turn her virtue into pitch" (2.3.364). He is also aware of Othello's own insecurities, and inferiority complex due to his race. Despite the fact that Desdemona, "had eyes, and chose [him]", Othello is convinced that she is unfaithful and gives as a reason:
Haply, for I am black
And have not those soft parts of conversation
That chamberers have, or for I am declined
Into the vale of years (3.1.402-5),
giving Iago fodder to work on his jealousy. Knowing that Cassio cannot hold drink, Iago manipulates him into drinking himself "full of quarrel and offence" (2.3.48), which action will lead him to a fight not becoming to his station, discrediting him in Othello's eyes, and allowing Iago to have the coveted position. He also reveals the means by which he will achieve his "monstrous" ends: by insinuating false motives to Cassio, who is handsome, charming, "framed to make women false" (1.2.323). Iago soliloquies further reveal his real thoughts about these