How we cite our quotes:
If I can fasten but one cup upon him,
With that which he hath drunk to-night already,
He'll be as full of quarrel and offence
As my young mistress' dog. (2.3.9)
Iago schemes to get Cassio drunk because he knows Cassio, who is kind of a mean drunk, will end up getting into a fight. Why? Because he wants Cassio (a soldier) to get in trouble with Othello (Cassio's boss/general) so that Desdemona will try to intervene on Cassio's behalf, which will make Othello jealous and suspicious. If this sounds overly elaborate and unrealistic to you, you're not alone. Literary critics often point out that much of Iago's plotting is, well, pretty implausible.
Ha! I like not that.
What dost thou say?
Nothing, my lord: or if--I know not what.
Was not that Cassio parted from my wife?
Cassio, my lord! No, sure, I cannot think it,
That he would steal away so guilty-like,
Seeing you coming.
I do believe 'twas he. (3.3.1)
Gosh. Iago is an evil genius, don't you think? After watching Desdemona and Cassio chit-chat from afar, Iago suggests that something naughty is going on between Cassio and Othello's wife. He never comes right out and says, "Hey Othello, look at your wife flirt with Cassio," but he implies there's something tawdry happening and then acts all innocent when Othello presses the point.
Get me some poison, Iago; this night: I'll not
expostulate with her, lest her body and beauty
unprovide my mind again: this night, Iago.
Do it not with poison, strangle her in her bed, even
the bed she hath contaminated.
Good, good: the justice of it pleases: very good. (4.1.38)
Whoa. We know that Iago is out to destroy Othello, but why is he so intent on destroying Desdemona? After convincing Othello that Desdemona has been cheating, he manipulates Othello into strangling Desdemona "in her bed." What's up with that? More importantly, what's up with Othello thinking that killing his wife in her bed is "just"? By this point in the play, Othello's mind has been completely warped.