The scene is the same as the opening of Act II. Lord Goring stands in front of the fireplace in Sir Robert's morning room. Summoned by a bell, the footman enters and tells Lord Goring Mabel has just returned from riding, Lady Chiltern is elsewhere in the house, and Lord Caversham is waiting for him in the library. Lord Caversham enters and asks his son if he has thought about their discussion of marriage. Lord Goring assures his father he has thought of nothing else, but Caversham, sensing his son's sarcasm, says he can never tell when he is being serious. Lord Goring states he can't tell either. Caversham encourages Goring to propose to Mabel, even though he doubts she would ever accept him. Lord Caversham then tells his son about Sir Robert's rousing speech to Parliament denouncing the Argentine Canal scheme, which the newspapers are praising as a turning point in his already excellent career.
Mabel enters and chats with Lord Caversham, ignoring Lord Goring as punishment for standing her up for their riding appointment. Finally, Mabel acknowledges Lord Goring, only to say she will never speak with him again. Pointedly, Mabel asks Lord Caversham if he can make his son behave more appropriately, but he responds by saying he has no influence over his son. Lord Caversham exists, leaving Mabel and Lord Goring to themselves. Mabel says people who fail to keep appointments in the park are horrid, and Lord Goring agrees. However, he tells her she must remain with him, because in her presence he cannot help but feel pleased. He then tells her has something to say and asks her to be serious for once. He declares his love and asks if she can love him in return, thus proposing marriage. Mabel quickly replies that she thinks it silly that he does not know how much she loves him, especially since the rest of London knows it. They kiss, and he tells her he was afraid of being refused.
Lady Chiltern enters and greets the couple before Mabel exits to wait for Lord Goring in the conservatory. Lord Goring tells Lady Chiltern he has obtained the letter from Mrs. Cheveley and burned it, and thus Robert is safe. With great relief, Lady Chiltern tells him how good a friend he has been to them. Lord Goring reveals that Mrs. Cheveley stole the letter Lady Chiltern had sent him and plans to send it to Sir Robert to "reveal" a non-existent affair. Lord Goring wants to tell Sir Robert the entire story to clear everything up, but Lady Chiltern forbids him to. They devise a plan to have Tommy Trafford intercept the letter before it reaches Sir Robert, but as Lord Goring moves to go speak to the secretary, he sees Sir Robert coming up the stairs with the letter in his hand.
Sir Robert enters and makes it clear he believes his wife wrote the letter to him. He shows pure joy that she needs him and wants him. He asks her to verify the truth of the letter, and with the urging of a pointed look from Goring, Lady Chiltern says she does indeed trust him. Lord Goring exits to the conservatory. Lady Chiltern then tells Sir Robert he is safe from the threat of Mrs. Cheveley, and relates how Lord Goring burned the letter. He proclaims how wonderful it is to see this one sin of his youth disappear and asks her if he should retire from public life. She suggests he should, but he fears he will surrender much by retiring. Lady Chiltern argues that rather than losing, he will gain much from this noble decision.
Sir Robert approaches Lord Goring and thanks him profusely for his help. Lord Caversham enters, congratulates Sir Robert on his brilliant speech and "high moral tone", and tells him the Prime Minister is hoping Sir Robert will fill his vacant seat in the cabinet. Sir Robert looks proud and triumphant, but after meeting eyes with his wife, he realizes he cannot take the offer. Sir Robert reveals to Lord Caversham that he plans to retire from public life and therefore must decline the offer. Lord Caversham is shocked and urges Lady Chiltern to convince her husband otherwise. She tells him she agrees with his decision and admires him for it. The two leave together, with Sir Robert looking rather bitter on his way to write his regrets to the Prime Minister.
Lord Caversham calls their behavior idiocy, while his son believes is an example of "high moral tone". Ironically, Caversham claims he does not understand such a "newfangled phrase". Lord Goring persuades his father to go to the conservatory where Mabel is waiting. Lord Caversham exits, and Lady Chiltern enters the room. Lord Goring asks her why she is following Mrs. Cheveley's example in trying to ruin her husband's career potential. At first she does not understand, but Goring explains that Gertrude is driving her husband out of public life by urging him to decline the vacant cabinet seat. He tells her that women are meant to forgive men, not judge them, and that by robbing him of his ambition she will eventually kill his love for her. She responds that Sir Robert wishes to retire from public life, but Lord Goring points out that Sir Robert will do anything to keep Lady Chiltern's love. However, the sacrifice he is about to make is one she should not ask of him. She ponders all that has been said, and finally agrees she has placed him on too high of an altar.
Sir Robert enters and hands Lady Chiltern the letter prepared for the Prime Minister, turning down the cabinet seat. She reads it and then tears it up, repeating much of Lord Goring's words regarding the appropriate roles of men and women, and her refusal to allow him to sacrifice and spoil his life. Gertrude says she can forgive Sir Robert, and that she finally sees that forgiveness is how women help the world.
Sir Robert embraces his wife, and thanks Lord Goring. Lord Goring then asks for his sister Mabel's hand in marriage. Sir Robert quickly changes demeanor, based on his belief that Lord Goring is still involved with Mrs. Cheveley. Lady Chiltern finally reveals to Sir Robert that it was she who Lord Goring expected at his house that night, and that the letter Sir Robert received was originally sent to Lord Goring. Upon understanding the complicated situation, Sir Robert immediately forgives his wife, saying she is the image of all good things. He turns to Lord Goring and consents to him marrying Mabel.
Mabel and Lord Caversham enter, and Lord Caversham is quite surprised at the engagement. He tells his son that he had better make an ideal husband, but Mabel counters she does not need an ideal husband. Rather, she merely wants to be a real wife to him. Lord Caversham agrees there is much common sense in that. He is very happy to hear Sir Robert has agreed to take the cabinet seat, and they all leave to have lunch. Sir Robert hangs back and asks his wife if it is merely pity, instead of love, that she feels for him. She responds that it is all love, and assures him their life together is beginning anew.
The complex action in this final portion of the play is quite notable. In addition to the confusion surrounding the note Lady Chiltern originally sent to Lord Goring, that Mrs. Cheveley then forwarded in malice to Sir Robert, and that finally unites Sir Robert and Gertrude, there are a variety of stolen conversations and entrances and exits that allow every aspect of the character's lives to find resolution. Clearly, the letter is a very important tool. It represents Lady Chiltern's love for her husband. Originally, she wrote that she needed and wanted Lord Goring, but only so she could speak with him about her troubled marriage, to which she held so dear. Re-sent to Sir Robert, the letter takes on new meaning, and with Lady Chiltern's revelation that she has in fact held her husband on too high of a pedestal, the statements inscribed in it apply directly to him. Thus, the letter seals their renewed love, and represents their bright future together.
The political thread in the play continues in Act IV. Ironically, the newspapers praise Sir Robert for his integrity, as they know nothing of the moral failure that almost caused his downfall. Lord Caversham tells Lord Goring the papers will never say anything like that about him, although in reality, Lord Goring seems to have lived with more integrity that Sir Robert. Lord Goring does not espouse a very high view of the House of Commons, and he certainly wants to avoid any involvement with a political life, yet his somewhat out of touch father and his morally failing friend are steeped in it. Thus, Wilde reveals his cynical views on the subject through Lord Goring, the character that mirrors him most.
In this same vein of public information, it is worth noting the power of the press in the play. Wilde understood the power of newspapers to make or doom a public figure. He promoted his own career through the media, and watched it ruin Parnell, a Scottish politician of the time who found great success and then was brought down through public scandals. One newspaper article brings Sir Robert public glory. Lord Goring, again a voice of Wilde himself, observes the irony, noting he certainly hopes the newspapers never discuss him in such terms. For the first three acts, the media was a threat to Sir Robert, and now it is a boost to his career.
The beginning of Act IV focuses on the separation between public and private information, and again, information is all-powerful. Sir Robert escapes his past because the public has no information about his corruption. Political corruption is only a problem to Sir Robert if it might possibly become known to the world. When he discovers Lord Goring has destroyed the corrupt letter, he rejoices. His own knowledge of his mistake does not haunt him, only the public disgrace it might cause. Even Lady Chiltern softens her staunch moral views after Sir Robert's name is protected from harm. Corruption only gets punished when it becomes a public matter, making political sense not a matter of principles, but rather of gamesmanship. Wilde criticizes the hypocritical society that condones this system of belief.
As Lord Goring refuses a career in politics, he refers to his youth as preventing him from taking on such serious responsibility. Goring sees youth as an art form, one with imperfections, but also breathtaking beauty. Goring wishes to live in a youthful world for as long as possible. In contrast, Sir Robert thinks of his youth as a reminder of his moral corruption and therefore tries to separate himself from it. Throughout the play, it would seem Wilde's perspective aligns more with Goring's, as he likens all the major characters to pieces of art. The small reference to art in this final act suggests that he continues to sculpt the characters throughout, and wants the reader to be aware of this process of creation. In this play, as the artist, Wilde promotes love over all other social forces, such as wealth or social status, as the key ingredient to happiness. In the end, Lord Goring, Mabel, Lady Chiltern, Sir Robert, and even Lord Caversham, are all pleased with the way things have turned out, and as with the opening scene, the tapestry of Boucher's "Triumph of Love" shines brightly in the final moments of the play.
Love and marriage triumph, and the roles of women and men in these aspects of life are defined clearly. Lord Goring fears a sensible wife will reduce him to idiocy very rapidly, but in advocating a sensible wife, Lord Caversham implies that a woman in touch with common social values, such as proper marriage, earns a respectable place in society. Lord Goring appears to take a cynical view of these notions, but also in a serious conversation with Lady Chiltern, argues that it is a woman's place to support her husband and forgive him for his faults. In fact, Lord Goring goes so far as to state a woman's life consists of "curves of emotion" and a man's consists of "lines of intellect". Moreover, he ironically extols the notion of the "ideal" Victorian woman, one who pardons rather than punishes her husband, and he urges Lady Chiltern to avoid following in Mrs. Cheveley's footsteps by trying to block her husband's success. Up to this point in the play, Lord Goring is a voice of moderate reason, but he disappoints the modern reader with this support of classic Victorian womanhood. In Goring's eyes, it appears women are inferior and should play supporting roles in their marriages.
Lady Chiltern originally adheres to the concept of an "ideal," morally perfect husband and marriage. However, her dream is shattered and she comes to terms with the reality of human faults. Interestingly, Lord Goring and Mabel have no foolish ideas about marriage and perfection, and when Lord Caversham offers his hope that his son will be an ideal husband, Mabel counters that she would rather him be a real husband. With this quick acceptance and demonstrated love of each other's faults, the reader clearly sees the mistake in Lady Chiltern's original expectations of perfection. Throughout the play, Mabel and Lord Goring have both vocally objected to the expectations society forces upon them, and balk at the notions of duty and respectability. Thus, their natural ease in entering a happy and tension free marriage seems to connote such disregard for the affectations of proper social behavior. It seems Wilde does not believe in the possibility of perfection, moral or otherwise, and believes those who accept their imperfections and avoid false affectation lead richer and more satisfying lives.