Our cult of decade anniversaries—the tenth of 9/11, the twentieth of “Nevermind”—are for the most part mere accidents of our fingers: because we’ve got five on each hand, we count things out in tens and hundreds. And yet the fifty-year birthday of a good children’s book marks a real passage, since it means that the book hasn’t been passed just from parent to child but from parent to child and on to child again. A book that has crossed that three-generation barrier has a good chance at permanence. So to note the fiftieth birthday of the closest thing that American literature has to an “Alice in Wonderland” of its own, Norton Juster’s “The Phantom Tollbooth”—with illustrations, by Jules Feiffer, that are as perfectly matched to Juster’s text as Tenniel’s were to Carroll’s—is to mark an anniversary that matters. (And there are two new books for the occasion, both coming out this month from Knopf: “The Annotated Phantom Tollbooth,” with notes by Leonard Marcus; and a fiftieth-anniversary edition, with a series of short essays by notable readers about the effect the book has had on their lives.)

Norton Juster (right) wrote the book. His neighbor Jules Feiffer did the illustrations. Illustration by Jules Feiffer

This reader, from the first generation, received a copy not long after the book appeared, and can still recall its curious force. How odd the first chapter seemed, with so little time taken up with the kind of persuasive domestic detail that fills the beginning chapters of the first Narnia book or “From the Mixed-Up Files of Mrs. Basil E. Frankweiler” or “Mary Poppins.” We’re quickly introduced to the almost anonymous, and not very actively parented, Milo, a large-eyed boy in a dark shirt—a boy too bored to look up from the pavement as he walks home from school. Within paragraphs, a strange package has arrived in his room. It turns out to be a cardboard tollbooth, waiting to be assembled. Milo obediently sets it up, pays his fare (he has an enviable electric car already parked by his bed), and is rushed away to the Lands Beyond, a fantastical world of pure ideas. The book breaks the first rule of “good” children’s literature: we’re in the plot before we know the people.

It’s a commonplace of scholarship to insist that children’s literature came of age when it began to break away from the authoritarian model of the moralizing allegory. Yet “The Phantom Tollbooth” is an old-fashioned moralizing allegory, with a symbolic point at every turn. Milo finds that the strange land on the other side of the tollbooth is sundered between words and numbers, between the land of Azaz the Unabridged, the King of Dictionopolis, and his brother the Mathemagician, the ruler of Digitopolis. The only way to reunite the kingdoms is for someone—why not Milo?—to scale the Mountains of Ignorance, defeat the demons, and release the banished princesses of Rhyme and Reason from their prison. (They were banished because they refused to choose between words and numbers, thereby infuriating the kings.) Along the way, each new experience makes funny and concrete some familiar idea or turn of speech: Milo jumps to Conclusions, a crowded island; grows drowsy in the Doldrums; and finds that you can swim in the Sea of Knowledge for hours and not get wet. The book is made magical by Juster’s and Feiffer’s gift for transforming abstract philosophical ideas into unforgettable images. The thinnest fat man in the world turns out to be the fattest thin man; we see them both. We meet the fractional boy, divided in the middle of his smile, who is the “.58 child” in the average American family of 2.58 children. The tone of the book is at once antic and professorial, as if a very smart middle-aged academic were working his way through an absurd and elaborate parable for his kids. The reality is that when Juster wrote “The Phantom Tollbooth” he was a young architect in Brooklyn, just out of the Navy, unmarried and childless, and with no particular background in writing or teaching, working out a series of jokes and joys for himself alone.

This became clear the other day, when the two creators of “The Phantom Tollbooth” were briefly sequestered in a Manhattan living room to talk about their work, and why it has lasted. Feiffer and Juster, both born in 1929, are like a pair of wryly benevolent uncles, with Norton the dreamy, crinkle-eyed, soft-spoken uncle who gives you the one piece of good advice you never forget, and Jules the wisecracking uncle who never lets up on your foibles but was happy to have you crash on his couch that night you just couldn’t bear going home. They interrupted, teased, and shpritzed each other as they recalled having blundered into a classic.

Juster, who speaks with the soft accents of the old Brooklyn, began recalling the origins of the book: “I had come back from the service, and I went to work in an architectural office. I was really kind of bored with everything, and I think, I’ll do a little book on cities. The kind of book that will be interesting for kids. I applied to the Ford Foundation for a grant—old saying, when God wants to punish you, he gives you what you ask for!—and got the grant.”

“Five thousand bucks you got!” Feiffer interjected.

“Was it that much? Anyway, I was up to my ass in worries and notes and couldn’t get it done. And so I took a vacation with friends, at the beach, Fire Island.”

“Probably with me!”

“No, it wasn’t you, Jules,” Juster added, though he explained that they already shared a roof. Stationed at the Brooklyn Navy Yard in 1956, Juster had found a garden apartment—“That’s what they call a basement room in Brooklyn,” Feiffer noted—in the Brooklyn Heights building where Feiffer was living, two floors up.

“My guilt for not doing it was overwhelming,” Juster continued. “So I started work on a little story about a kid who didn’t know what to do with himself, and didn’t like to learn. It was Milo! At that point, I just kept writing. When I finished the book, I felt very worried and very guilty. I thought the Ford Foundation was going to demand the money back.”

“I wondered what became of our money,” Feiffer said.

“After the book came out, I never heard from them. Long time later, I found that they were delighted about it.” Juster went on, “In fact, I didn’t know I was writing the book. I knew it was about this little kid named Milo, wrote bits and pieces everywhere. At a certain point, I needed something to tie it all together. It was all so haphazard. Jules’s wife, Judy, said, ‘Write a two-page synopsis.’ And I did, and it had nothing to do with what happened in the book. And of course the demons appeared very early in my thinking but didn’t arrive in the book until very late. Judy took it to Jason Epstein, a real major player. He was doing, quite coincidentally, a series of reprints of children’s books. The Looking Glass Library.”

“Very classy-looking,” Feiffer put in.

“At that time, everyone was writing down to children. There were these lists: no kid should ever open a book and find anything in it that he didn’t already know. ‘The Phantom Tollbooth’ was the only original book Jason did. He was a wonderful editor, and he used to scare the hell out of me. At a certain point, he’d stop and say, ‘It’s your book. Do what you want with it.’ I’d get rigid.”

Two childhood experiences shaped the book. One was a curious mental condition. “I had an ailment called synesthesia,” Juster explained, pronouncing the word carefully. “I could only do numbers by colors.” His mind—in a way that will be familiar to readers of the memoirs of that fellow-synesthete Nabokov—made instant, inescapable associations between a number and a color. “I can still remember a few: 4 was blue, 7 was black, and so the only way I could do math was by associating colors.” As frequently happens with synesthetes, the condition extended to words and images. “One of the things I always did was think literally when I heard words. On the ‘Lone Ranger,’ they would say, ‘Here come the Injuns!’ and I always had an image of engines, of train engines.”

The other shaping experience was listening to the radio. As both artists stress, having a pure stream of sound as your major source of entertainment meant that your mind was already working imaginatively, without your necessarily realizing it. “It’s impossible today!” Feiffer said. “Everything is visual. We had thought balloons in our heads that played jazz riffs off what we read and what we heard, and that’s what led to the imaginative restructuring of reality.”

Juster agreed: “Sometimes I go into schools now and say, Let me start a story. And what you get from the kids is almost exactly what comes out of the TV set. The kids have very few images of their own. We came home from school, listened to hours of fifteen-minute serials, Jack Armstrong and Don Winslow, and it was great.”

The book was published in 1961, and no one had much hope that it would find an audience. “Everyone said this is not a children’s book, the vocabulary is much too difficult, the wordplay and the punning they will never understand, and anyway fantasy is bad for children because it disorients them,” Juster said, four million copies later. “I thought, O.K., it will come out, and end on the remainder table.”

What does make the enduring magic of “The Phantom Tollbooth”? As with every classic of children’s literature, its real subject is education. The distinctive quality of modern civilization, after all, is that children are subjected to year after year after year of schooling. In the best-loved kids’ books, the choice is often between the true education presented in the book—say, Arthur’s through animals at the hands of Merlyn, in “The Sword in the Stone”—and the false education of the world and school. The child being read to (and the adult reading) is persuaded that self-reliance is a better model for learning than slavish obedience.

Each story of self-education has, to be sure, its period slant. Lewis Carroll’s Alice learns to resist the world’s nonsense, however seductively dressed as logic, but she also learns, Victorianly, that manners matter. In “The Wind in the Willows,” Mole is educated by Rat to mess around in boats and prefer the river to the burrow, but he’s also taught, as schoolchildren were in Edwardian England, to accept communality as the highest of virtues, and standing out too much, pushiness, as the worst of sins (particularly as displayed by the obviously outsider Mr. Toad). In the colonial French “Babar,” the elephant is educated in how to be a colonial Frenchman. In the “Mary Poppins” books, which first appeared in the thirties and forties, the Banks children are educated by their upright-seeming but poetic nanny in the Dionysian joys—they learn that the stars come down to go Christmas shopping, and you get the moon if you wish for it.

Milo is the most watchful and passive of classic protagonists, the hero as freshman. An American boy of the late fifties, he is very much an empty vessel. Juster said he was actually concerned, when he was halfway through writing the book, that Milo would seem too empty—too socially isolated and too apart from the world. “I was a curious kid, but not like that,” he added. Milo learns to trust the wisdom of others—to admire the truly learned—and to find the marvellous not in the heavens above or in the middle earth below but in the textbooks at hand. He’s the perfect first-generation American undergraduate, scanning the course catalogue, wide-eyed.

Milo is also one of the few protagonists in children’s literature—Dorothy is another—who have a wiser best friend throughout their journey, in this case Tock, the watchdog. Just as Dorothy learns from the smart Scarecrow, Milo learns from Tock’s timekeeper’s knowledge. Milo doesn’t educate himself; he gets educated. His epiphany is that math and reading and even spelling are themselves subjects of adventure, if seen from the right angle. The point of “The Phantom Tollbooth” is not that there’s more to life than school; it’s that normal school subjects can be wonderful if you don’t have to experience them as normal schooling.