The Republic's tone is authoritative, even in a collaborative, serious, and well-intentioned discussion. The fact that Socrates ends his dialogues with allegedly complete and valid arguments and is so well-respected by other characters for his argumentative prowess results in a tone that is far more authoritative than Socrates would proclaim himself to be. Indeed, despite claiming to know nothing, Socrates consistently demonstrates through the asking and answering of questions that he knows much, and that it is rather his interlocutors who know little.
The seriousness of The Republic's subject matter—from justice and knowledge to the immortality of soul, among other topics—creates a solemn tone. The importance ascribed to answering these questions is matched only by a sense of genuine curiosity: after all, who wouldn't want to know what justice is so that they might be able to achieve it?
At the same time, the exploration of the limits of knowledge creates a wary tone. For instance, the allegory of the cave is a cautionary tale that urges against taking any knowledge except knowledge of Forms for granted. However, rather than undermining the characters' arguments themselves, this empirical skepticism emphasizes the importance of Platonic Forms: ideal essences of which material goods are only an imperfect reflection. The existence of Forms suggests that true knowledge is possible, if only for the highly skilled philosopher, enabling a sense of certainty in a book containing dizzying argumentation.