Themes
Power of Communication (from Course Hero)
The characters in The Phantom Tollbooth learn the value of clear communication. The brothers King Azaz and the Mathemagician fail to communicate or understand each other because one relies on words and the other on numbers. They are more interested in opposing each other and proving their superiority, and this mistrust and miscommunication between the brothers has led to the banishment of their sisters, Rhyme and Reason. The Princesses know that both words and numbers are important tools for learning and communicating. But they can't prevail until the brothers are forced or tricked into reconciling.
Other characters, too, learn the importance of communication. Faintly Macabre has come to understand while she's in prison that her silencing the people of Dictionopolis was unwise. Similarly, the Soundkeeper realizes that banishing all sound is not the answer to dealing with unpleasant noises.
Juster's use of puns and other wordplay throughout The Phantom Tollbooth is at the heart of the novel's charm and humor. His playfulness with language as a mode of communication drives the plot and character development in significant ways, so the novel itself stands as a testament of the power of communication and the capacity of language to teach and entertain.
The Value of Education (from Spark Notes)
Though Milo never actually finds himself in the classroom, The Phantom Tollbooth is primarily a book written in praise of education. The plot of a bored little boy who is inspired by travels in the City of Words, the Forest of Sight, the Valley of Sound, and the City of Numbers seems to spell this out clearly. The most consistently pressed concept in the book is, without a doubt, the importance of the various lessons Milo learns through his journey. It is only by using the knowledge he has gained that Milo is able to fight his way past the demons who inhabit the Mountains of Ignorance. The princesses Rhyme and Reason, who represent wisdom, another major theme, acknowledge the importance not only of what Milo has learned, but also of how he has learned to use it.
Knowledge and Learning (from Course Hero)
Over the course of his journey, Milo comes to understand not only the importance of learning but the power of knowledge. He goes from being indifferent and apathetic to eager and interested to learn. All of the events in the book are opportunities for Milo to learn something new about himself and provide important lessons. He realizes that he needs to expand his vocabulary and learn more about math. He learns to value both silence and noise and to accept the value of rhyme and reason. Milo receives gifts throughout the novel that help him learn valuable lessons. Each gift is given to Milo to help impart specific knowledge.
Milo comes to see that his boredom—which is his constant state at the beginning of the story—comes from his inability to see that there's a lot of things that are worth learning and that the world is an interesting place if one takes the time to pay attention. He realizes how much he doesn't know, which inspires him to truly want to learn. Learning is not a waste of time, and understanding what to do with knowledge gives one great power. Milo sees his room, his life, and his world, differently now.
Appreciating the Things of Everyday Life (from Spark Notes)
Milo's boredom is largely the result of his inability to appreciate the world around him. His bedroom is the perfect example of this: it is practically overflowing with toys, all of which Milo finds totally unengaging. Through his travels in the Lands Beyond, he meets a number of people who also have taken the things in their life for granted. The inhabitants of the city of Reality, for one, begin hurrying about without stopping to appreciate the beauty of their city. As a result, the city slowly crumbled away into nothing. Similarly, the residents of the Valley of Sound become so unappreciative of beautiful sounds that the Soundkeeper was compelled to impose utter silence on the whole of the valley. Through his travels, Milo learns the folly of taking things for granted so much so that he decides to postpone any further travels in the Lands Beyond in favor of enjoying the things in his bedroom.
Learning to Use Common Sense (from Spark Notes)
One of the defining characteristics of the Lands Beyond is the presence of quite a lot of nonsense. Inhabitants of this fantasyland engage in all sorts of ridiculous behavior, most of which shocks even Milo. Juster uses the nonsense of certain situations, such as the Royal Banquet, for great comic effect while simultaneously underscoring the lack of a natural order. Rhyme and Reason, we eventually learn, are imprisoned in a faraway castle and much of the nonsense Milo observes has only sprung up since their departure. Milo himself, of course, is in need of some common sense. His quest to find Rhyme and Reason therefore is both literal and figurative. On the one hand, he must learn all sorts of lessons in order to truly appreciate common sense. On the other hand, he must physically journey to the Castle in the Air to release the princesses.
Escaping Boredom (sparknotes)
At first Milo, simply, is bored. His tendency to be consistently bored seems to change when he first enters the Lands Beyond, but once Milo finds himself in the Doldrums he is right back where he began. Thankfully, Tock enters the scene and helps teach Milo about the value of time and how to make the most of every minute. Then Milo finds himself in the clutches of boredom at later points in the story, such as when he is in the Dictionopolis prison or when he is waylaid by the Terrible Trivium. With the help of his friend Tock and the lessons he has learned through his journeys, however, Milo manages to overcome boredom and eventually becomes so good at inspiring himself that he no longer needs the flash and excitement of the Lands Beyond to hold his attention.
Fantasy Enriches Reality (from Course Hero)
Milo embarks on a journey of the imagination. Once he passes through the tollbooth, he leaves reality behind in his bedroom and meets fantastic characters and finds himself in bizarre situations. All of these magical adventures will help shape his reality. Milo learns that imagination and creativity are important parts of life, and they often result in altering one's perception of reality.
At the end of the book, Milo looks at his room differently. He was once completely unable to be excited or interested in his surroundings. In this way he was like the people of the city of Reality, as Alec Bings describes them. The people in that city stopped paying attention and caring about the city around them. The city got uglier and dirtier and finally disappeared altogether. When Milo returns from his journey, it is as if he is seeing his surroundings for the first time. His room and his world are no longer boring and dull to him. He sees the potential in his surroundings, and he will seize that opportunity to make something of his time in school and at home. His journey has led him to discover the power of learning and the importance of acquiring knowledge. Reality and fantasy merge into one and Milo's appreciation of make-believe becomes part of his everyday life.
SOURCES: https://www.sparknotes.com/lit/tollbooth/quiz
Source https://www.coursehero.com/lit/The-Phantom-Tollbooth/themes/