Hermione researches the plight of the house-elves, who are slaves to their masters and must do whatever their masters require. The house-elves are uneducated, and unable to argue or think for themselves. They are kept as unpaid workers by wealthy wizarding families, and their treatment depends on the mercy of their masters. Hermione finds this despicable, and she works throughout the book to liberate this oppressed minority. The enslavement of the house-elves mirrors the enslavement of wizards, good and bad, at the hands of Lord Voldemort. Whether by swaying them to follow him willingly, or by placing them under the Imperius curse to cause them to follow him without knowing it, he gradually pulls much of the wizard community into his power, to work for his whims and to perform his malicious tasks toward the goal of wiping the world clean of all but pure-blood wizards. Dumbledore leads the crusade against wizard enslavement just as Hermione leads the one against house-elf enslavement, and hence, this book protests enslavement on both grand and small scales.
In this story, almost nothing is achieved by a single person alone. Harry, brave and resourceful as he is, could not triumph in the Triwizard Tournament alone. Hagrid and Moody helped him prepare to get past the dragon; Cedric and Dobby helped him decipher the golden egg and rescue his underwater victims. Although Harry gets through the maze with his own ability, he could not have escaped Voldemort without the protective charms of his wand's affiliation with Voldemort's wand. Furthermore, Harry is marked by his parents' sacrifice to keep him alive, so that even when he appears to be doomed, he often is protected by a connection to them. Almost nothing that Harry does in any of these books is achieved alone; he approaches challenges with courage and a basic groundwork of skill, but the friendships and connections he has made along the way enable him to succeed. Harry reciprocates this aid within his community. He encourages Hagrid to return to teach, and he lets Cedric know about the dragon. He also lends Moody his Marauder's Map. The boarding-school setting of Hogwarts allows for an insular, tightly bound community in which each person's actions affects somebody else, and this connectedness is a key factor in the successes of these stories.
J.K. Rowling portrays the comings-of-age of her main characters. This novel shows the largest development from one year to the next. Ron, Harry, and Hermione have entered adolescence. Harry is hesitant to tell grown-ups that his scar hurts, as he is concerned about his self-image. He is also, for the first time, very aware of Cho Chang. Ron is more self-conscious than ever about his lack of money and his shabby dress robes, and he is defensive about Harry's fame. Ron is also more sarcastic than ever in his scorn for Percy. The first feelings of romantic attraction are stirring throughout this book. Sexual tension between Ron and Hermione causes numerous arguments in this book, and it is clear that much of the book's events reflect subtle changes within the maturing process of the characters themselves.
J. K. Rowling works to dispel our preconceived notions about the Harry Potter characters and about the magical world that they inhabit. Her presentation of the merpeople is one example of challenging a façade. She plays to our expectations with a beautiful, shapely, stereotypical mermaid in the painting in the prefects' bathroom; then, underwater, she reveals a village of hideous creatures with long, green, tangled hair, sallow gray skin, broken yellow teeth, and eerie appearances. They are not remotely what we think Harry will find at the bottom of the lake, and they are not supposed to be, for even mythology must have its secrets, and even Harry, who is still learning about the wizard world, has his own, often misguided, notions about how things should be. The same is true of Mad-Eye Moody, who is among Harry's favorite teachers before he reveals himself to be the villain responsible for placing Harry directly within Voldemort's line of fire. Again, Snape proves himself to be innocent, although all of the signs point otherwise. Almost nothing in this book is what it seems, teaching the reader not to jump to conclusions, but to gather evidence slowly and to prepare to expect the unexpected.
When Hagrid introduces the class to the blast-ended Skrewts, he makes a distinction between the males and females. The former have stings, and the latter have suckers on their bellies. This comparison is symbolic of the adolescent need to make more of a distinction between the sexes. Ron also notices in this book, for the first time, that Hermione is in fact a girl, and Harry finds himself daydreaming not about fame or glory, but about Cho Chang.
Different characters' speech patterns reveal their levels of education. Wizards speak in proper English, and Hagrid, who is half-giant and not fully educated, drops his H's and slurs his words together a bit sloppily. House-elves have no sophisticated mastery of language. They use terrible grammar, referring to themselves in third person and using almost exclusively short, exclamatory sentences. They speak in a manner inferior to that of wizards, and they cannot express themselves clearly or persuasively.