What are the motifs in The Phantom Tollbooth by Norton Juster?

Language is a recurring idea in the novel. If the "message" of the novel is that wisdom ought to be pursued and ignorance shunned, and if the "warning" that goes with that message is that all things should be done in moderation, then those themes are conveyed to the reader in a playful, humorous way by the author's use of language. The whole world created in the Lands Beyond is a world where words have power and physicality. Language is not just a form of communication in the novel. It defines the very being of everything it names.