Quote 19
IAGO
Call up her father,
Rouse him. Make after him, poison his delight,
Proclaim him in the streets; incense her kinsmen,
And, though he in a fertile climate dwell,
Plague him with flies. Though that his joy be joy,
Yet throw such changes of vexation on 't
As it may lose some color. (1.1.74-80)
Yikes. When Iago talks about corrupting Brabantio's opinion of his fair daughter, Desdemona, he uses the language of poison and plague, which seems pretty appropriate given the nature of Iago's manipulation. When Iago tattles on Othello and Desdemona for eloping, he capitalizes on Brabantio's xenophobic attitude toward mixed race marriages. Here's what Iago says to get Brabantio riled up against Othello:
Even now, now, very now, an old black ram
Is topping your white ewe. Arise, arise;
Awake the snorting citizens with the bell,
Or else the devil will make a grandsire of you:
Arise, I say. (1.1.89-93.1)
Check out "Race" if you want to think about the implications of this.
Quote 20
IAGO
But for my sport and profit. I hate the Moor,
And it is thought abroad that 'twixt my sheets
He has done my office. I know not if 't be true,
But I, for mere suspicion in that kind,
Will do as if for surety. (1.3.429-433)
Iago cites multiple and incompatible motives for wanting to destroy Othello. Earlier, he said he hates Othello because "the Moor" passed him over for a promotion, but here, he tells us he hates "the Moor" because he's heard a rumor that Othello has been hooking up with Iago's wife, Emilia, "twixt [Iago's] sheets." It's just not clear whether or not we, as an audience, can believe anything Iago has to say.
Quote 21
IAGO
Virtue? A fig! 'Tis in ourselves that we are thus or
thus. Our bodies are our gardens, to the which our
wills are gardeners. So that if we will plant nettles
or sow lettuce, set hyssop and weed up thyme,
supply it with one gender of herbs or distract it
with many, either to have it sterile with idleness or
manured with industry, why the power and corrigible
authority of this lies in our wills. (1.3.361-368)
When Iago makes an analogy between gardening and exercising free will, we're reminded of the way that Iago is the ultimate master gardener, so to speak. Part of what makes him such a brilliant manipulator of Othello is his ability to plant the seeds of doubt and jealousy in Othello's mind.