“Fantasy is our imaginary life's blood,” Tamora Pierce told me recently. "It is simply an extension of our myths and legends, our fairy tales and our folktales. It is the stories we tell ourselves to give shape to our dreams and desires, and the forces that we suspect are working beyond where we can see right now. That's why we write it . . . that's why people respond to it so passionately. [Fantasy writers] are speaking directly to people's souls." In the same interview, Chris Riddell, illustrator of the Edge Chronicles, focused on the world-making aspect of fantasy writing. "What I love about fantasy, in that sense as a practitioner, is the ownership of the fantasy world," Riddell said. "I enjoy figuring out how you live in another world."

Pierce and Riddell voiced two perspectives to consider in thinking about good fantasy. On the one hand, fantasy can be a quest for understanding the human condition; on the other, it can be an exercise in expansive creative play. The two features aren't mutually exclusive, but looking at recent evidence, one might conclude that they are. Strange creatures, objects of power, unusual customs and foods; lengthy descriptions of landscapes, warty faces, and the spectacular show of magical weapons — physical description dominates current fantasy. In the movies, "great special effects!" is often code for works eschewing depth and development of character, as well as intellectual content and originality — and these features have become rare and special indeed in fantasy literature for children and young adults.

But fantasy in the western world has almost always meant an imaginative exploration of human nature and metaphysical truths, from stories of the gods and heroes of Greek and Roman literature to allegorical battles for the soul in medieval Christian tales. It isn't just about the pleasure we derive from envisioning alternate worlds; it's about worlds whose concrete features and schemes of action are metaphors that carry a probing examination of who we are as humans. The medieval Latin word for metaphor is translatio, and that is what the best fantasy is: a translation, in accessible language and story, of difficult notions. Like the Greek word metaphor, translatio literally means "a carrying across." The best fantasy does just that — carries us from the concrete to the abstract, from a satisfying narrative experience to a moment of articulate wisdom.

I arrived at this conclusion by letting my mind drift to what I consider the best fantasies, then asking myself how and why certain works stood out. Why does Peter Dickinson's The Blue Hawk (1976) persistently come to mind when I meet a ten- or twelve-year-old who wants a great fantasy? It's true that Dickinson's desert landscape, breathtaking action, and engaging protagonist make for a compelling story; but even more, it's because of the big ideas he conveys with memorable vividness.

At the beginning of The Blue Hawk, temple acolyte Tron, who has been selected as "goat" (the boy given ritual license to disrupt tradition), feels directed by the gods to remove the blue hawk whose life is to substitute for the king's in an annual sacrificial rite of renewal. Tron's intervention changes the course of history and sways the balance of power — a narrative move familiar in fantasy and realistic fiction. But while a lesser writer might have Tron overthrow authority or become the means of debunking religion altogether, Dickinson explores through him the human impulse to codify religion at the expense of a grander concept of the divine. Tron imagines that there are "true" gods — "inside us, all round us, like the air we breathe without noticing." Dickinson moves from ideas of personalized gods to a concept of the divine that's open, unembodied — a short course in comparative religion.

The Blue Hawk thus invites invigorating theological musings. It also makes kids confront the very perception Pierce voices above — the idea of story as metaphor. Tron can only express his new understanding by telling a story, giving "shape to his dreams," as it were. When questioned, he says, "This is only a story. It's a might-have-been. It's a way of explaining to myself what's happened to me." Later, he says the familiar stories about the gods are "just a sort of picture of what really happened, something that won't go into pictures, but something with the same sort of rightness and wrongness in it." Dickinson leaves his readers with that clear thought, that fantasy is "a sort of picture," not representational but bearing truth. He makes us think about how story works in our own world, even about why we write fantasy. The Blue Hawk is remarkable because in addition to giving us a wonderful quest story, Dickinson presents a consideration of ritual, religion, and the role of metaphor in human understanding.

Why do I go into such detail, quoting here and there? Because in the best fantasy, it's the precision of language, the words with which the author chooses to put things, that leads us to whatever originality the story carries. A perfect example of this rich exactitude is Margaret Mahy's The Changeover: A Supernatural Romance (1984), simply one of the best possible fantasies for teens.

The Changeover is set in the real world — a mundane subdivision in a suburb in New Zealand. Laura Chant knows her little brother Jacko is being consumed by a rapacious spirit; she enlists the help of Sorry Carlisle, a boy she has recognized as a witch, to save him. But Sorry's mother and grandmother, both witches, claim that the only way to rescue Jacko is for Laura to "change over" and become a witch herself.

"Your journey is inward, but will seem outward," Sorry's mother Miryam tells Laura as she prepares to change over. Here Mahy lets her readers into a truth about good fantasy: the physical landscape and visual changes are an external language telling us about something inward.

"Sometimes I think all women are imaginary creatures, as Sorry chooses to put it," says Miryam. "He doesn't mean that we're simply imagined, you know, but that our power flows out of the imagination, and that's the faculty that makes magicians of all of us." Mahy so clearly blends imagination and magic (both "mage" words) that all readers must see the connection. She makes us entertain the thought that magical lands and magical people are words that carry a meaning beyond themselves. Laura makes her inward/outward journey through a visually arresting landscape, and Sorry's grandmother Winter interprets it for her: "The bare forest down there stands for the forest that, by some accident, grows green in Miryam, Sorensen and me." That very notion of "stands for" lets readers into one of the great riches of the reading experience — the realization that our stories can be pictures of abstract meaning, even of wisdom.

The story of Jacko's rescue would be engrossing on its own, but Mahy entwines a very recognizable psychological realism in and about the story's magic. In the beginning, she tells us that Laura's changing body fills her "with a tentative optimism," and once, when Laura remarks that her dress is getting too small, Sorry responds, "Not so! It's you that's changing, not the dress." The image of the changeover is as much a powerful metaphor for the body's development and for sexual awakening as it is for the amazing possibilities of imagination, and Mahy makes sure her readers have the language to make that connection. "Something is going to happen," Laura thinks as Sorry approaches her. "She was going to be kissed. On one side of a kiss was childhood, sunshine, innocence, toys and, on the other, people embracing, darkness, passion and the admittance of a person who, no matter how loved, must always have the quality of otherness, not only to her confidence, but somehow inside her sealing skin."

Mahy's "changeover" is a metaphor for something born organically of the depths of the human psyche: the creative powers of the imagination and the creative powers of sexuality. Each word in her novel connects integrally with the multiple meanings carried by its central metaphor — a hallmark of great fantasy. The Changeover gives shape to understanding and desire — not just to understanding the fears and pleasures of emergent sexuality or the leap of faith that growth is, but also to the reason we conceive or write of magic at all: because it expresses more truly and more mysteriously how we experience reality.

I would love to go on to point out the genius of numerous other best fantasies — Terry Pratchett's Wee Free Men, Megan Whalen Turner's King of Attolia, Jonathan Stroud's Bartimaeus trilogy, and many others. But if there's one thing I've learned, it's that you can't describe a good fantasy in a few words of generalization. Every great fantasy is great in its own way, and that's because real insight and artistic originality must be unique to its author. To describe why a fantasy is superlative, you must go directly to the words with which it is conveyed. The harder it is to summarize the way the story and the language work, the more likely it is that you're dealing with a fantasy worth your time and thought. If a fantasy's characters fit into recognizable roles; if the imagery is unrelated to any inward journey; if there's no phrase or conversation that encapsulates what that journey has been, no moment that causes you to go back and reread with new understanding — why then, you're dealing with a run-of-the-mill work.

It's not so much the invented world and magical beings of a fantasy that make it remarkable. Although the creation of an alternate world is a natural and delightful form of play (Tolkien thought it was how we imitated God the creator), if the inventor has no real insight to impart, it's humdrum stuff. Fantasists have unique access to the metaphor of magic, but the deeper they are willing to go in their exploration of human nature and how we make meaning, the more rewarding, wise, and enduring their inventions will be.

From the September/October 2006 issue of The Horn Book Magazine.