Act IV opens still in Lady Wishfort's house, as the rest of the play will take place there. Lady Wishfort and Foible are in conversation about the imminent arrival of Sir Rowland, with Lady Wishfort reminding Foible of the various things that need to be made ready and asking about her appearance and demeanor for when he comes. Lady Wishfort also wishes for Sir Wilfull to call upon Ms. Millamant that night, though Fainall's plot to get him drunk seems to be beginning offstage. Lady Wishfort exits, telling Foible to get Millamant and Sir Wilfull together and then to call on her while she is with Sir Rowland so that they are not alone for too long.
Ms. Millamant and Mrs. Fainall enter and Foible tells Ms. Millamant that Mirabell has been waiting to talk with her, though Lady Wishfort wishes for her to go spend time with Sir Wilfull. Ms. Millamant says that she will not see Mirabell, and instead begins reciting lines of poetry. She then tells Foible to show Sir Wilfull in and asks Mrs. Fainall to speak with him, herself continuing to pace around reciting verse. Sir Wilfull enters and Mrs. Fainall encourages him to pursue his interest in Ms. Millamant now, since circumstances are perfect with them alone, she contemplative, and he a bit drunk. Sir Wilfull is timid and tries to escape the situation, but Mrs. Fainall leaves the two of them in the room together, locking the door behind her.
Sir Wilfull approaches Ms. Millamant, but she continues reciting verse. He does not understand the verse, revealing is bumbling less-than-learnedness. Ms. Millamant makes her self difficult, insulting his idea to take a walk together and saying she hates diversions of both the country and the town. Sir Wilfull beats around the bush for a while longer, until Ms. Millamant asks him to leave her. Chagrined, he leaves through of the other, unlocked door in the room.
Laughing, she recites another line of verse, and the rhymed couplet is completed by Mirabell as he enters the room. They discuss marriage together, and Ms. Millamant takes a feminist tack, demanding a list of privacies and conditions including sleeping in late, not engaging in public displays of affection of any kind, and being able to give and receive visits and letters without "interrogatories or wry faces." Mirabell parries back, accepting her conditions but placing requirements on her including forbidding secretive relationships with other women and telling her she must like her own face as long as he does, rather than attempting to change it with night-masks. When he begins to talk about "breeding" Ms. Millamant attempts to cut him off, but he goes on to say that she should not wear a corset which would squeeze his child's head "like a sugar-loaf."
Mrs. Fainall enters as Mirabell requests to kiss Ms. Millamant's hand to seal the deal, and they welcome her. Ms. Millamant somewhat reservedly professes her love for Mirabell aloud and allows him to kiss her hand but nothing more. Mrs. Fainall warns that her mother, Lady Wishfort, is going to come soon and so Mirabell had better leave. Mrs. Fainall also announces that Sir Rowland has been having success with Lady Wishfort but that Lady Wishfort has had to leave him to deal with a very drunk arguing pair - Sir Wilfull and Petulant. Mirabell exits and Anthony Witwoud enters laughing, announcing that the drunken argument going on is based on nothing but that the two men are very enraged nonetheless. Petulant enters, drunk. He asks Ms. Millamant whether she can love him, and he and Witwoud spar with words. Petulant leaves angrily and the scene ends with Witwoud saying it was Fainall's advice to get so drunk.
Scene II opens in the dining room of Lady Wishfort's house with the same configuration of people - Witwoud, Ms. Millamant, and Mrs. Fainall - along with Lady Wishfort and a now very drunk Sir Wilfull. Lady Wishfort berates Sir Wilfull for his drunkenness and in response he sings a song. Sir Wilfull now proposes marriage to Ms. Millamant, again referencing his life outlook of always doing things he sets his mind to. He sings again and monologues at length, going so far as to touch upon Ms. Millamant's virginity. Ms. Millamant leaves disgustedly, taking Mrs. Fainall with her, and Lady Wishfort scolds him again to with he again sings and talks at length. Foible enters to tell Lady Wishfort that Sir Rowland grows impatient and Lady Wishfort asks Anthony Witwoud to deal with his half-brother. The two men exit and Lady Wishfort briefly laments that Sir Wilfull is not ready to marry Ms. Millamant, at least until he has come back from abroad.
Waitwell, disguised as Sir Rowland, now enters, and the audience sees him in upper class costume for the first time. He woos her heavy-handedly and Lady Wishfort seems taken by it. According to the plan, he pushes for them to get married as soon as possible. Foible enters and summons Lady Wishfort to receive a letter, which the audience should remember has been sent by Ms. Marwood to reveal Mirabell's plan. Unaware, Waitwell and Foible flirt while Lady Wishfort is out of the room, Waitwell calling Lady Wishfort "the antidote to desire." Lady Wishfort re-enters with the letter and calls for a dance, which is performed onstage. As she makes to open in, Foible recognizes Ms. Marwood's handwriting on the outside and Waitwell attempts to get the letter away from her. Waitwell attempts to convince her that the letter is from Mirabell and meant to slander him, and Waitwell promises, perhaps hyperbolically to kill him for this rudeness. His words work; Lady Wishfort tells the man she supposes to be Sir Rowland to come back with the marriage for her that night, so long as he comes back not having fought to death with Mirabell.
Act IV contains more verse and song than any other act. Building on the directorial choices of the prior act, the director may choose to have these moments (Ms. Millamant's verses while Mrs. Fainall speaks to Sir Wilfull, Sir Wilfull's drunken songs, the dance performed for Lady Wishfort and Sir Rowland) brought to attention or kept short. Focus can also be drawn to the words of the verses and songs which continue to be wittily romantic in content. For example, Ms. Millamant's background repetition and apparent interposition of Sir John Suckling's poem and "The Story of Phoebus and Daphne, Applied," if spoken loudly enough, might underscore the youthful amorousness of Sir Wilfull's fear of proposing his love to her.
Poetry is also used to demonstrate in the in sync nature of some relationships in the play - Ms. Millamant and Mirabell and later Waitwell and Foible. In the former example, Ms. Millamant recites a line from "The Story of Phoebus and Daphne, Applied" about Phoebus and Mirabell counters with the second line of a rhymed couplet, a line about the beauty of Daphne. Their foolish love parallels that of the characters in the poem and his completion of the couplet, especially with a rhyme, is a poetic display of true connection with one another. In the case of Foible and Waitwell the situation is perhaps even more pronounced, as they are not quoting but speaking together one of the rhymed couplets that end each act. Foible uses her addition to parallel the flirtatious secrecy of the exchange when Lady Wishfort briefly left the room and again demonstrate the strength of their relationship though forced upon them.
A certain Restoration feminism is displayed in the requirements of both Ms. Millamant and Mirabell regarding their marriage (freedom to talk to whomever, his requirements about keeping her real face and shape). Perhaps the most surprising is Mirabell's request that she not create a fake face with makeup when she ages, even with so much focus for women in the play on not aging to retain their power. This "proviso scene" is one of the most famous in the play as the "legalese" is used to cover a joyful lovingness.
Of some interest is Sir Wilfull's phrase "Wilfull will do't," a phrase he seems intent to live his life by. This motto is contrasted with his humorous timidity earlier in the act, but adds to his apparent foolishness with an element of impulsiveness. This same impulsiveness perhaps contributes his getting as drunk as he does, losing the chance to pursue Ms. Millamant and allowing for the chance of a Millamant and Mirabell marriage.
The acting of Waitwell as Sir Rowland is an important directorial choice, as it easily lends itself to comedy but this comedy may be directed at making fun of lower class people, upper class people, or both through any ineptitude at acting in the ways of the upper class. This choice will also impact Lady Wishfort's character in what it means that she does not notice his act. Fun can be had at her desperateness or perhaps a hardness of sight, both embarrassing signs for an aging woman.