Act IV begins some time later and takes place in Higgins' laboratory-living room. The scene opens on the night after there has earlier been a great success where Eliza was presented as a duchess at an ambassador's garden party, as was stipulated in the original wager between Higgins and Pickering. Eliza has been a smashing success. Thus, when the scene opens, Higgins and Pickering are celebrating their triumph. (By this time, the actual financial terms of the wager are insignificant; Pickering has helped train Eliza and is sharing in the triumph, even though he has lost the wager.)
Eliza enters; she is brilliantly dressed in impeccable taste but her "expression is almost tragic." Immediately, Higgins begins to look for his slippers, and he is so busy congratulating himself on his great success that he is unaware that Eliza has left the room and has returned with his slippers; to fetch Higgins' slippers is apparently another accepted aspect of her training.
As Higgins and Pickering sit down and discuss the great triumph of the day, we hear that Eliza has been a tremendous success not only at the garden party, but also at the dinner party and at the opera later. Higgins then admits that after the first few minutes, it became obviously apparent that he was going to easily win his bet with Pickering, and, as a result, he was bored for the rest of the time. In contrast, Pickering rather enjoyed himself, especially the very professional manner in which Eliza carried the entire charade off. Pickering then retires for the evening, followed by Higgins, yelling to Eliza to put out the lights.
Alone, Eliza gives vent to her pent-up fury as she flings herself furiously onto the floor, raging. At that moment, Higgins returns, looking for his slippers, which Eliza hurls at him with all her force. He is totally baffled by her display of anger. He is furthermore astounded by her calling him a "selfish brute" who is ready to throw her back into the gutter now that she has won his bet for him. Higgins is dumbfounded at her presumptuous claim; he refuses to acknowledge that she had anything to do with his winning the bet. The entire feat was accomplished by his coaching and his brilliance. When she physically attacks him, asking what is to become of her, Higgins restrains her and says, "What does it matter what becomes of you?" Higgins' brusqueness, however, subsides, and he relents enough to question her about her anxieties and to offer a glass of champagne to relieve the strain of the day. He assures her that she will feel better now that the garden party is over. Eliza's concerns, however, clearly and seriously involve the future. She asks: "What am I fit for? What have you left me fit for? Where am I to go? What am I to do? What's to become of me?" Even though both Mrs. Pearce and Mrs. Higgins have warned Higgins about this dilemma, he has obviously never given it a moment's thought. He can't imagine that she will have any difficulty in finding something to do — or even in marrying someone. After all, not all men are "confirmed old bachelors" like Higgins and Pickering. Maybe Mrs. Higgins could find a young chap for her. Eliza then informs him that all that she has ever done is sell flowers; now, as a lady, she can't even sell flowers; all she can hope to do is sell herself. She wishes Higgins had left her where he found her. (She has apparently forgotten that she came to see Higgins, not the other way around.)
Higgins returns to Eliza's original desire to work in a flower shop, and he suggests that Pickering could perhaps set up Eliza in her own shop. Higgins thinks this solution settles everything, and once again, looking for his slippers, he prepares to retire. But Eliza has one more question. She wants to know what clothes belong to her, personally — that is, what clothes may she keep and what clothes belong to the "experiment." After all, Higgins and Pickering might need some of the clothes for the next girl they pick up to experiment on. She reminds Higgins of her past: "I'm only a common ignorant girl; and in my station I have to be careful." Higgins tells her that she can take all the clothes, but she cannot have the jewelry; it was rented. She antagonizes him further by asking him to take the jewelry to his room so there will be no "risk of their being missing." She also returns a ring which he bought her, but he throws the ring so angrily into the fireplace that Eliza crouches over the piano, her hands over her face, crying, "Don't you hit me." Higgins now feels wounded, and when Eliza tells him that he had better leave a note for Mrs. Pearce because she (Eliza) won't do his errands any more, he leaves, slamming the door savagely and calling Eliza "a heartless guttersnipe." Alone, Eliza senses her triumph over the master; thus, she quickly kneels and digs the ring out of the ashes. She finds it, considers it for a moment, and then flings it down and goes upstairs in a rage.
This act presents the completion of the artist's masterpiece; here is the fully realized Galatea that Pygmalion created in the form of the living Eliza. Here, we see a person completely transformed from the "guttersnipe" that we saw in Covent Garden in the first act. At the beginning of the act, both Pickering and Higgins are so absorbed in their own triumph that both fail to realize that the success of the experiment belongs as much to Eliza as it does to their teaching. In fact, when Eliza suggests that she won their bet for them, Higgins repudiates her claim vehemently: "You won my bet! You! Presumptuous insect! I won it." What neither Pickering nor Higgins takes into account is the stupendous effort that Eliza herself has contributed to the entire endeavor. As we shall see in the next act, Mrs. Higgins certainly recognizes Eliza's contribution, but both men are so absorbed in their own achievement that they fail to grasp the fact that Eliza has worked exceedingly hard to be able to speak like a lady; as a result, she developed an intense devotion and loyalty towards her two masters — not a love devotion, but a deep and sincere devotion and also a strong desire to please. Thus, at the beginning of this act, when the men ignore her, her pent-up fury turns to rage. The image which Shaw uses is that of a well-trained puppy dog fetching its master's slippers. At the beginning of the act, Eliza does, in fact, fetch Higgins' slippers. The men, however, fail to pet and admire the "puppy" for her achievements, and therefore the trained puppy turns on its masters. In the next act, this image of the trained dog fetching slippers will be continued and will be developed as a central metaphor. Here, the slippers are dropped, literally, by having Eliza throw them at the master. However much Eliza has changed outwardly, this act of rage aligns her with the Eliza of Covent Garden of the first act.
In the original myth, Pygmalion had to pray to the gods to give his creation a soul. What Higgins as a creative artist did not realize was that his Galatea had a soul already. He has been able to polish the outside to a high degree of mechanical perfection, but he failed to note that at the same time, his creation was developing an inner soul and a mind of her own.
Whereas Mrs. Pearce's and Mrs. Higgins' first concern was what would happen to Eliza after the transformation, this has now become a question of major importance for Eliza. In a conventional type of romantic comedy, the ending would probably show the total success of the experiment with the audience leaving the theater with the knowledge of Eliza's triumph at the ambassador's party and with Eliza and her master's falling in love, just as it happened in the myth. However, Shaw was interested in what happened after the triumph. And Eliza herself asks, what is she fit for, and where is she to go, and what will become of her? Higgins has been so completely involved with his experiment and the success of it that this question has never seriously entered his mind. Even now, when it is pointed out to him, he cannot take it seriously. Eliza knows that she absolutely cannot return to her old way of making a living, for she is now trained to be a lady and has no visible means to support herself in the position for which she is now trained. Thus Higgins has created a work of art without considering what he will do with this work of art after its exhibit is over. When Higgins suggests some sort of marriage, Shaw is making another dig at social standards. That is, when Eliza was a flower girl, she sold flowers and not her person; now that she is Lady Eliza, she can't sell flowers anymore (that would be beneath her) but she can sell herself.
At the end of the act, Eliza needles Higgins in a desperate attempt to break through his outer veneer. In her own repressed emotions, she wants to see him hurt just like she has been hurt; she wants to penetrate the god-like distance that Higgins surrounds himself with; thus, she taunts him until she makes him lose his temper, and she is able to enjoy the spectacle of a so-called, self-proclaimed god losing his self-control — that is, Higgins is a "god" now made human, with human emotions and fury.