Drama, Realism
Shaw has a lot to say here: heavy stuff about language, society, and the soul. Lucky for us, in this case he likes to show and tell.
We get long speeches from Higgins about how language is what makes us human, about the great significance of his work with Eliza, and sometimes it seems like Shaw is simply using him as a mouthpiece. But we get enough perspectives on other issues—Alfred Doolittle on the undeserving poor, Mrs. Higgins on the place of women in society—and enough heated arguments to raise doubts about the truth of Higgins's statements.
Until we get to the fourth act, the play seems like it's headed toward the usual sort of Hollywood ending. Eliza's going to be transformed into an intelligent, elegant, eloquent, and eligible young woman, grumpy old Higgins is going to learn a lesson or two about manners and compassion, somebody will get married...
Instead we get two more acts full of arguing and passive-aggressive behavior with no real end in sight. We do get a marriage, in the end, but it's not your neat little fairy tale kind. (Papa Doolittle's not really much for sticking with a single woman. He wouldn't even be thinking about wedding bells if it weren't for that whole "middle class morality" thing.)
In the end, Higgins seems to be the only one who's sure how things will turn out. Eliza will come back, he tells his mother, but we have no real way of knowing if she will. As it turns out, the play's central question isn't, "Can you pass off a flower girl as a duchess?" but, "What can you do with her once you succeed?"
As attractive and, perhaps, truthful as Higgins's talk about the soul and language is, Shaw forces us to put it to the test. As Higgins tells Eliza:
HIGGINS: The great secret is not having good manners or bad manners, but having the same manner for all human souls. (5.197)
We have to wonder, though: can this apply to the real world, or is this nothing more than a fantasy?