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.