In The Phantom Tollbooth, words are very important. In fact, for the folks who live in the Lands Beyond, words are pretty much the most important things in the world. Language is everything to the people of Dictionopolis. It's their bread and butter. Literally! Linguistic tricks, puns, and plays on words can help people to travel [like the car that "goes without saying" (6.56)] or cause them injury [like "falling off a log" (3.86)]. Knowing what to say and when to say it can save your life – or at least, save you from boredom. But in Digitopolis, it's numbers (which you might think of as another type of language) that run the show. And it's the conflict between words and numbers that has created the bitter fight between these two cities. Will they kiss and make up? We sure hope so.
The lessons Milo learns from King Azaz in the kingdom of Dictionopolis show that words will always be more important than numbers.
The lessons Milo learns from the Mathemagician in the kingdom of Digitopolis show that you don't need to rely on words to communicate.