In the prologue, Congreve uses verbal irony (saying the opposite of what he means, through the actor who plays Fainall) to set up the witty satire that is about to follow:
Satire, he thinks, you ought not to expect;
For so reformed a town who dares correct?
To please, this time, has been his sole pretence;
He’ll not instruct, lest it should give offence.
Should he by chance a knave or fool expose,
That hurts none here, sure here are none of those.
In short, our play, shall (with your leave to show it)
Give you one instance of a passive poet.
Who to your judgments yields all resignation;
So save or damn, after your own discretion.
This sounds at first like the highest flattery of the audience. Congreve claims his play is not like other Restoration comedies, which satirize society, because the audience is "reformed" and surely beyond reproach. He does not mean to "give offence" by "instructing" them in how to behave because they already know how to behave. He admits that he might "expose" some of the characters as fools, but he insists that these foolish characters do not reflect anyone who is in the audience. Congreve presents himself as a "passive poet" (rather than an active satirist) who just wrote a play for fun and is presenting it to the audience. They are free to judge the characters as they wish. In fact, Congreve suggests that the audience probably knows better than him which characters ought to be judged.
But Congreve does not really intend this prologue as straightforward flattery. The first clue to this is that the actor who plays Fainall, a chronic liar and manipulator, delivers the speech. By getting the audience to believe they are beyond reproach, Congreve has already gained a point against them. As the play goes on, it becomes clear that only a fool, like Lady Wishfort, can be taken in by this kind of flattery. The play goes on to critique a society of "manners" where people avoid "giving offence" openly by making backhanded compliments and performing politeness more than embodying it. Congreve is having his own fun with performing manners. The prologue sounds extremely polite but is itself one long backhanded compliment.
Nonetheless, the prologue does soften the blows of the play's satire. The fact that Congreve makes fun of his audience by doing exactly what he critiques (couching criticisms in politeness) establishes right away that the satire is good-natured. He is not above is own critique, and he thinks the pettiness of all this "polite" rudeness is at least as amusing as it is bad for society.
In Act 2, Scene 2, Mrs. Fainall asks Mirabell to walk with her to finish the story that was interrupted the night before, when her mother threw him out of her house. She uses verbal irony to explain why it makes sense for the two of them to walk together without Fainall:
[Fainall] has a humour more prevailing than his curiosity and will willingly dispense with the hearing of one scandalous story, to avoid giving an occasion to make another by being seen to walk with his wife. This way Mr Mirabell, and I dare promise you will oblige us both.
Mirabell has suggested that Fainall will disapprove of his gossiping with Mrs. Fainall, ruining reputations. He has reason to believe that Fainall with disapprove: earlier in the day, Fainall described the gossip sessions at Lady Wishfort's house as horrible, frivolous, judgmental affairs where people satiate their appetite for scandal on the corpses of ruined reputations. In this passage, Mrs. Fainall retorts that her husband is simply more obsessed with appearances than satisfying his own curiosity about his neighbors. She claims that as someone obsessed with appearances, Fainall wouldn't want to create yet another scandal by letting himself be seen walking together with his wife. By this logic, Fainall will be happy to let Mrs. Fainall and Mirabell go on together without him.
On the surface, Mrs. Fainall is claiming that her husband is simply worried about politeness and public image. In the world of the play, everyone is supposed to have a healthy concern for public image, so this is a polite enough claim about him. But the idea that it would be fodder for gossip if she and her husband were seen together indicates that their marriage is not in good shape. They must not spend much time together, at least in public. Furthermore, underlying Mrs. Fainall's claim that her husband has "a humour more prevailing than his curiosity" is the idea that Fainall has somehow overridden his basic humanity. How could someone not want to know the latest neighborhood gossip? She does not specify which "humour" prevails. In this period, a healthy person was supposed to a balanced mix of the four humours (phlegm, blood, yellow bile, and black bile). Fainall has too much of one. As the play goes on, it seems likely that it is yellow bile. Too much yellow bile was said to make people hot-tempered and ambitious.
Mrs. Fainall thus uses the pretense that everyone (even Fainall) is concerned about manners to insult her husband by walking off with another man—and her former lover, no less! If he were to stop them, it would disprove her backhanded compliment and reveal that Fainall is not governed by the rules of politeness. After several backhanded compliments, Mrs. Fainall at last outwits Fainall and alerts the audience to the fact that something is off about him.
In Act 2, Scene 4, Mrs. Fainall and Mirabell discuss a plan of Mirabell's. Mrs. Fainall asks about who Mirabell got to play his fake uncle. Dramatic irony comes into play here:
MIRABELL: Injustice to you, I have made you privy to my whole design, and put it in your power to ruin or advance my fortune.
MRS FAINALL: Whom have you instructed to represent your pretended uncle?
MIRABELL: Waitwell, my servant.
MRS FAINALL: He is an humble servant to Foible, my mother’s woman, and may win her to your interest.
In Act 1, Witwoud mentioned how Mirabell's uncle was coming to town and had plans to cheat him out of his inheritance. This moment is when it becomes clear that Mirabell was in charge of things all along. The audience gets the satisfaction of realizing, after the fact, that Witwoud and everyone who thinks Sir Rowland is Mirabell's antagonist is completely misreading the situation. There is an entire group of people (Mirabell, Mrs. Fainall, Foible, and Waitwell) who are in the know, and now the audience as part of that group as well.
This is one of many twists and turns in the play, where dramatic irony is layered on top of itself. The audience is always trying to stay one step ahead of the characters and keep track of who knows what, but characters keep revealing juicy tidbits like this and changing the landscape of the plot. In this instance, the audience is forced to completely reevaluate their interpretation of an earlier scene. As satisfying as it is to be brought into the loop regarding Mirabell's scheme, it is also a reminder to be on the lookout for the plot to turn on its head once more. A wit can turn into a fool at any time.
In Act 2, Scene 8, Waitwell and Foible arrive in the park. Mirabell lightly admonishes Waitwell for being late, and Waitwell responds in a way that highlights the situational irony of his happy new marriage:
MIRABELL: [....] Sirrah Waitwell, why sure you think you were married for your own recreation, and not for my conveniency.
WAITWELL: Your pardon, sir. With submission, we have indeed been solacing in lawful delights; but still with an eye to business, sir. I have instructed her as well as I could. If she can take your directions as readily as my instructions, sir, your affairs are in a prosperous way.
Waitwell's response is supposed to be comical: as was common in Restoration comedies, Waitwell makes a bawdy joke about his satisfying sex life with Foible, his new bride. "Solacing in lawful delights" simply means that they have been enjoying the fact that they are legally allowed to do whatever they want sexually now that they are married. Waitwell also hints that Foible, who has essentially married into Mirabell's service by marrying Waitwell, is going to make a good servant because she is good at following orders in the bedroom.
The crass jokes serve more than to delight the audience. They also demonstrate that Waitwell and Foible's marriage is going better than might be expected given that it came about as part of Mirabell's plot. Ironically, a marriage designed to trick people is actually a passionate marriage. By contrast, the other marriage represented in this act was Fainall and Arabella's marriage. The two of them supposedly have a more "real" marriage than Waitwell and Foible, but Arabella joked that she and her husband would spark rumors if they were seen walking together. The "real" marriage seems to be utterly devoid of passion if Fainall and Arabella are so rarely even seen together.
Waitwell's joke about the intertwined nature of sex and business also has a serious note: in the social environment Congreve was trying to capture, business, pleasure, performance, and authenticity are all intermingled. This is not necessarily a bad thing, but it can be. In the case of Waitwell and Foible's marriage, the fact that business is part of it is no problem because they have a genuine relationship as well. What Congreve criticizes is marriages like Arabella and Fainall's, which clearly have no basis in love or passion to accompany everything else.
In Act 3, Scene 6, Foible carefully finds out what Mrs. Fainall knows about Mirabell's plot. The scene is famous for the dramatic irony that unfolds while Foible tries to make sure the information doesn't get into Mrs. Marwood's hands:
Madam, I beg your ladyship to acquaint Mr Mirabell of his success. I would be seen as little as possible to speak to him. Besides, I believe Madam Marwood watches me.
Foible takes care not to reveal the plot to someone who might reveal it to Marwood or Lady Wishfort. She already believes Marwood is on the case. Ironically, Marwood overhears the entire conversation from her hiding place in a nearby closet. The audience, knowing that Marwood is eavesdropping, is invited to laugh when Foible says that she is worried Marwood is watching her. She, of course, means that Marwood has generally been keeping a close eye on her, not that Marwood is literally watching her right now. This is one of many examples in which the audience has the chance to see characters' plans foiled, even while they think they are being clever. Congreve is always making fun of the people who think they are wits and not fools: no one is exempt from being a fool, even a character as favorably depicted as Foible.
Marwood emerges from the closet after everyone leaves (taking a back route to avoid Mrs. Marwood) and delivers a soliloquy. She is essentially talking to herself, but in a way that allows the audience to see what is going on inside her head. The audience is now privy to Marwood's thoughts and motivations, which are somewhat different to what she reveals to other characters. This moment of dramatic irony at once positions the audience in an omniscient position (none of the characters know as much about what is going on as the audience knows) and also reminds the audience that there are probably more revelations to come.
In Act 4, Scene 4, Millamant and Wilfull have a comic scene shot through with dramatic irony. Millamant is reciting poetry, but Wilfull believes she is speaking to him:
MILLAMANT: That foolish trifle of a heart – Sir Wilfull!
SIR WILFULL: Yes – your servant. No offence I hope, cousin.
MILLAMANT [repeating]: I swear it will not do its part,
Tho’ thou dost thine, employ’st the power and art.
Natural, easy Suckling!
SIR WILFULL: Anan? Suckling? No such suckling neither, cousin, nor stripling; I thank heaven, I’m no minor.
MILLAMANT: Ah rustic! ruder than Gothic.
SIR WILFULL: Well, well, I shall understand your lingo one of these days, cousin; in the meanwhile, I must answer in plain English.
The fact that Wilfull doesn't understand the poetry, or even that Millamant is reciting poetry, is designed to make the audience feel wittier than him. The audience has already been clued into the poem by an earlier exchange between Millamant and Mrs. Fainall, in which Mrs. Fainall indicated that the poem is by John Suckling. This was a clever move on Congreve's part. Even audience members who don't recognize the poem right away are well set up to laugh at Wilfull for misunderstanding the situation. As is often the case, this moment starts to set up a dichotomy between Wilfull the fool and all the wise people in the audience. This scene is delivering on the prologue's promise to keep the audience separate from the people being called witless.
But the very move Congreve pulls to make sure the audience can recognize the poem also serves to subtly undermine some audience members' confidence in their wit. Those who relied on Mrs. Fainall's identification of the poem must pretend they knew it all along. Congreve has also suggested that poetry is artful and often performative. For instance, Millamant only curls her hair with love notes her suitors have written in verse. Millamant's halting performance of Suckling's poem gets in the way of her communicating effectively with Wilfull. The entire misunderstanding could have been avoided not only if Wilfull recognized the poem, but also if Millamant stopped reciting it for a moment to have a conversation. What's more, audience members who are too focused on the poem, or too busy congratulating themselves for recognizing it, might also have a hard time following the thread of the conversation. The audience and Millamant are as much the butt of the joke here as Wilfull is.
In Act 4, Scene 12, Lady Wishfort pleads with Waitwell (who she believes is Sir Rowland) to pardon her long absence to deal with her drunken nephew and his friends. Waitwell's response uses imagery that is laden with verbal irony:
My impatience madam, is the effect of my transport; and till I have the possession of your adorable person, I am tantalized on a rack, and do but hang, madam, on the tenter of expectation.
A rack is a torture device across which a prisoner's body is stretched. While the prisoner's hands and feet are tied at either end, rollers gradually pull the ends apart so that all the joints in the body are pulled apart. The stress on the entire body is very painful. The image of Waitwell hanging on a rack suggests that he is absolutely helpless to do anything because he is so enamored of Wishfort. He is her prisoner. The image is at once flattering and unflattering: he lets Wishfort know that he likes her a lot, but he also chides her a little for leaving him in such a vulnerable position. She is not being a good host, and manners are important to her.
Beneath all this, there is a second meaning to Waitwell's words here. He is waiting "on the tenter of expectation," but not the kind of expectation he allows Wishfort to think. Instead, he is dying to know whether he is going to be able to keep her convinced that he is Sir Rowland long enough for Mirabell to pull off his blackmail scheme. This is a fun caper for Waitwell, possibly in part because he is a servant who now gets to humiliate someone of higher social rank than him. Although his image suggests that he is Lady Wishfort's prisoner, there is a way in which the reverse is true. Because Lady Wishfort is so desperate for attention from a suitor, Waitwell has her captive to his affection. He is gradually stretching her to her limit, seeing how long he can keep her under the spell of his feigned romance.
In Act 4, scene 15, it seems that Marwood has at last foiled Mirabell's plan by delivering Wishfort a letter revealing that Sir Rowland is really Waitwell in disguise. In a twist of situational irony, Foible and Waitwell are able to use Wishfort’s hatred of Mirabell to further convince her that Sir Rowland is a real person:
Oh, what luck it is, Sir Rowland, that you were present at this juncture! This was the business that brought Mr Mirabell disguised to Madam Millamant this afternoon. I thought something was contriving, when he stole by me and would have hid his face.
Wishfort's deep suspicion of Mirabell and his ethics should lead her to spot his manipulation. The entire point of Marwood's letter is to disabuse Wishfort of the belief that this sham uncle of Mirabell's is real. This whole thing is a setup, and Mirabell is behind it all. This really is manipulative behavior on Mirabell's part, and Wishfort has reason to believe the worst of him. Ironically though, her low opinion of him backfires on her. Knowing that she will believe the worst of Mirabell, Waitwell and Foible convince her instead that Mirabell wrote the letter as another manipulation tactic. Supposing that Sir Rowland actually is real, Mirabell has an incentive to convince Wishfort that he is a fake so that he won't cheat Mirabell out of an inheritance. Wishfort, who desperately wants Sir Rowland to be real because she relishes his romantic attention, is all too ready to believe this version of the story. Where Marwood and the audience expected Mirabell's entire scheme to come crashing down with the delivery of this letter, it instead flourishes.
Not only does this make for a fun and surprising plot twist, it also allows Congreve to satirize the way a petty grudge like Wishfort's can lead to reductive thinking and underestimation of a rival. Wishfort's opinion of Mirabell is a little too low, at least in terms of his cleverness and competence. He is capable of far more than writing a fake letter to get what he wants. He has created an entire fake person to carry out a Restoration version of a modern "catfishing" scheme. Wishfort makes it easier on him than it needed to be.