Philinte recounts to Éliante the story of Alceste's partial apology to Oronte in Court. Éliante calls Alceste's behavior "peculiar," but also "noble and heroic" because of Alceste's honesty. Philinte and Éliante then discuss Alceste's affection for Célimène, questioning his decision to pursue a relationship with someone whose affections seem so fickle. Philinte says that Alceste would do better to turn his attention to Éliante. Éliante states that, although she would be reluctant to be Alceste's second choice, she would probably allow herself to fall for him. Philinte tells Éliante that he would like to win her favor if she fails to win Alceste's.
Having found a letter written by Célimène to Oronte, Alceste claims he has proof of her deceit. Alceste asks Éliante to help him avenge himself against Célimène, proposing that Éliante become the object of his affections. Éliante maintains that Alceste's relationship with Célimène is not lost, and Alceste vows to confront Célimène about her infidelity. Philinte and Éliante exit.
Furious, Alceste confronts Célimène, claiming that he cannot take responsibility for what his "wrath" might lead him to do. Célimène admits to writing a letter to Oronte, but considers Alceste's behavior ridiculous. She does not demonstrate any guilt for what she has done. Distraught, Alceste demands that Célimène tell him that the letter was intended for a woman, so that Alceste's heart and mind can rest, assured that she is loyal to him.
Alceste's protestations stir Célimène to anger, and she extorts that he does not deserve her love. Now in anguish, Alceste proclaims his love for her, hoping, perhaps against his better judgment, that she will remain his.
Alceste's manservant, Du Bois, enters in a panic, demanding that Alceste pack to leave at once. Du Bois claims that he has spoken with a man who has notified him that Alceste is in danger of arrest—a result of his ongoing lawsuit. Unable to glean enough information from Du Bois, Alceste leaves to find out more about the matter at hand. He tells Célimène that he will be back to speak with her.
In Act IV we learn that even the confident Célimène hides a sensitive interior life. The attention she pays Alceste indicates a true attraction to him, betraying the image of a carefree girl she puts forth. Célimène speaks vaguely of the love she feels for Alceste (IV.iii), and Éliante tells Philinte of Célimène, "She's not entirely sure of her feelings herself." In breaking apart the masks of his leading characters, Molière shows that The Misanthrope is not a simple, typical satire. The play is a comedy, but it seeks also to comment on human emotions and relationships. By the end of Act IV, we can no longer accept that Alceste and Célimène—or any of the other characters, for that matter—are stereotypes. Subtle human emotions and their accompanying actions are now at play. Even Alceste seems less inclined to criticize, as he seeks a reason to forgive Célimène for her love letter to Oronte. Ironically, Alceste wants to be lied to, to be told that Célimène sent the letter to a woman. The man who adheres to a doctrine of honesty would have that doctrine suspended to put him at peace.
Act IV welcomes the one true, pleasantly surprising love affair in the play, that between Philinte and Éliante. Although the depth of their mutual attraction is not fully realized in Act IV, a sweet and sincere romance begins. In uncovering this relationship, Molière hints that our—and his own—attention has been misplaced. The real heroes of the story have been hiding up until this point. The Philinte-Éliante love affair is made all the more touching by the simplicity of these characters. Neither has any outstanding or particularly unique characteristic, unlike the dramatically unique Alceste and Célimène, whose relationship is the focal point of the story. Molière implies that individuality, in its extreme form, deters love. Apparently, something other than a defining trait draws Philinte to Éliante. By avoiding the drama of Court society, Philinte and Éliante are able to establish a deeper connection, one not based upon superficialities. We might even argue the rest of the play is a red herring to this romance. In spite of all of the efforts to woo Célimène, nothing ever really happens in that arena. The one solid accomplishment of the play is the eventual union of Philinte and Éliante, which is finalized in Act V.
As the love affair between Philinte and Éliante begins to blossom, the relationship between Alceste and Célimène continues to fall apart. When Alceste discovers a letter he believes to demonstrate Célimène's deception of him, he attempts to apply the same type of justice to her as has been used against him. He says the letter "convicts" her, and he marvels that she can "still persist in the face of this overwhelming evidence" (IV.iii), seeking to try her for her "crimes" against him. Alceste appears to think that if he can be tried for hurting Oronte's feelings, so can Célimène be brought to justice for shaming him. Thus, although Alceste finds his lawsuit ridiculous, he tries to apply the same tenets of law to his relationship with Célimène. However, Alceste lacks the strength to carry out his verdict. He admits to being hopelessly drawn to Célimène. Again, Molière juxtaposes formality with emotion. In this case, Alceste attempt at legal rationality loses out to his own visceral impulses. Ultimately, he asks Célimène to lie about intended recipient of the letter to make him feel better.
As the act draws to a close, Alceste receives news that he must leave or be subject to arrest. This moment, in Act IV, scene iv, marks the final crisis of the plot. If Alceste decides to leave, he must also decide if his troubles with Célimène are worth resolving. In vowing to return to finish his conversation with Célimène, Alceste shows a willingness to compromise not present in earlier acts. His misanthropy appears to weaken as his situation becomes more desperate.