In Act 2 Scene 3, How is Iago’s plan beginning to work?

Cassio has gotten drunk and into an arguement provoked by Roderigo. Cassio was supposed to be on duty so Othello is already really angry. Othello isn't rational when angered and he is easy play for manipulation. Iago is going to entreat Desdemona to appeal to Othello on Cassio's behalf.

He's sure that when Cassio is drunk he'll get quarrelsome. Furthermore, Roderigo is already drunk, and Iago has gotten three proud Cypriots drunk, too. All of these men are supposed to join Cassio on the watch, and Iago is sure that when these drunks all get together, Cassio will do something that will get him into deep trouble.

Soon enough Iago sees that his plan is on the road to success, because in comes Cassio with Montano and some others, saying, "'Fore God, they have given me a rouse already" (2.3.64). "Rouse" is a word for a drink of liquor; we might call it a "pick-me-up," and it looks like Cassio is already feeling pretty good. Now all Iago has to do is keep the party going, so he calls for wine, sings a drinking song, and talks about how the English can drink everyone else under the table. The drinking song and the drinking talk succeed in getting Cassio even more in the mood, and he drinks "To the health of our general!" (2.3.86). Then Iago sings another song, one about King Stephan and his breeches. It's not exactly a drinking song, except that it's silly and pointless, but Cassio exclaims, "'Fore God, this is a more exquisite song than the other" (2.3.98). When Iago asks him if he'd like to hear the song again, Cassio answers, "No; for I hold him to be unworthy of his place that does those things. Well, God's above all; and there be souls must be saved, and there be souls must not be saved" (2.3.101-104). This seems to show that Cassio retains some dim awareness that he shouldn't be drinking on duty, but then he rationalizes his drunkenness by saying "God's above all" and many of us are sinners.

The singing and drinking have made the time pass, and Cassio tells the rest that it's time to go on watch, but as he goes he reveals just how drunk he is by denying that he is drunk. He says, "Do not think, gentlemen. I am drunk: this is my ancient; this is my right hand, and this is my left: I am not drunk now; I can stand well enough, and speak well enough" (2.3.112-115). Most of us know that when someone starts talking like this, it's time to take his car keys away from him, but Cassio is off to command the watch which is supposed to guard the town and keep the peace during the night.

Montano is about to join Cassio and the others, but Iago detains him by making a comment about Cassio: "He is a soldier fit to stand by Caesar / And give direction: and do but see his vice; / 'Tis to his virtue a just equinox, / The one as long as the other" (2.3.121-125). A "just equinox" is an exact balance of dark and light; Iago first says that Cassio is a great soldier, then says that he is as great a drunk as he is a soldier. He adds that he's afraid that Cassio's drunkenness will sometime make him betray Othello's trust and disturb the peace of Cyprus. Montano asks if Cassio is often drunk, and Iago answers that he gets drunk every night, that he can't go to sleep without getting drunk.

It's obvious that Iago is lying. He certainly doesn't think that Cassio is a great soldier and he knows that Cassio isn't a habitual drunk. What's not so obvious is just why Iago is lying. Perhaps he wants to prepare Montano to draw the right conclusions when Roderigo gets into a brawl with Cassio. Perhaps he wants to plant the idea that Othello should share responsibility for any of Cassio's mistakes, since Othello appointed Cassio to his post. Or maybe Iago is just lying for the fun of it.

As Montano is saying that Othello should be told of Cassio's weakness, Roderigo appears, and Iago, in a quick aside, sends him away again, saying "I pray you, after the lieutenant; go" (2.3.137). It appears that Montano hasn't even seen Roderigo, because he keeps on talking about Cassio, saying that it's a pity that Othello should trust someone such as Cassio, and that Othello ought to be warned. Iago replies he can't do it because Cassio is his good friend. Just then Iago begins to reap some of the fruits of his scheming. We hear someone yelling "help!" and Roderigo comes running on stage, chased by Cassio. Montano asks what's the matter and Cassio rages, "A knave teach me my duty! I'll beat the knave into a twiggen bottle" (2.3.147-148). Apparently Roderigo has made some insulting remarks about how Cassio is performing his duties, and Cassio is determined to make him pay. Roderigo is drunk, and Cassio is threatening to stuff him back into the wine bottle he came from.

At this point Iago gets lucky. He had thought that Roderigo could get Cassio angry, but he didn't foresee the involvement of Montano, who is a leading citizen of Cyprus. Montano tries to calm Cassio down and apparently puts a hand on him, because Cassio, in his drunken rage, says, "Let me go, sir, or I'll knock you o'er the mazzard" (2.3.153-154). "Mazzard" is a slang word for "head," and saying "knock you o'er the mazzard" is like saying "knock your block off." Montano replies, "Come, come -- you're drunk" (2.3.155). This turns out to be exactly the wrong thing to say to Cassio, and they start to fight.

As Montano and Cassio are fighting, Iago sends Roderigo to "go out, and cry a mutiny" (2.3.157). He wants Roderigo to do whatever he can to stir up a riot. Roderigo goes, and in a moment we hear an alarm bell being rung, as though the town were on fire. Meanwhile, Iago pretends to try to stop Cassio and Montano from fighting, all the while yelling for help, so that people will come and see Cassio's shame.