Scratch any science fiction of fantasy writer and the red wound of argument appears: sf is the subgenre of fantasy or fantasy is the subgenre of science fiction. It is an old fight. However, there is one kind of writing in which the two are so intermingled, it is hard to know which is and which and that is the time travel story.

Essentially there are two kinds of time travel -- into the future or into the past. Sometimes the viewpoint character does the traveling: back to King Arthur's court, back to the Children's crusade, forward to converse with the Eloi. Occasionally it is another character who comes forward of back in time to interact with the main players: Mayne's drummer boy in Earthfasts, the child Hatty in Tom's Midnight Garden, or Nesbit's psammead.

The implements of travel -- those things which allow the traveler to slip through the streams of time like a minnow in a brook, are many. There is Taliesin's tuning fork in Nancy Bond's A String in the Harp; there is an elaborate device in H.G. Wells' Time Machine and in Crusader in Jeans. There are silver pins, magic mirrors, wardrobe cupboards, and conjunctions of moons, planets, stars. In my new book, The Devil's Arithmetic (Viking, 1988) a young Jewish girl of the 1980s opens the door for Elijah at the family seder and finds herself back into a past that she has been steadfastly refusing to remember by three things: the great neediness in her family of Holocaust survivors, the open seder door, and the familiar childhood chant "Ready or not, here I come."

None of us is really ready for a trip into the past or into the future. We al fight time. Children, eager and fearful at once, want to grow up and yet remain young. Peter Pan is a very perceptive book.

Patricia MacLachlan told me a very poignant story about her oldest son John going out on his very first date to a prom. The entire family had been exited, but Patty found herself getting more and more depressed as the evening progressed. Her little boy was growing up. When he got home, she fought the temptation to quiz him on it. But the next morning, when she came downstairs, a bit nervous and sensitive about what to say, she heard a strange noise. There, on the living room floor, was John with his younger brother and sister, toy car in hand. The noise Patty had heard was John going "Vrrrrrrooom." Boy and man at once.

Children, especially at the time they are reading time travel novels, are a bit like Walter de la Mare's "Poor Jim Jay" who

Got stuck fast
In yesterday... Round veered the weathercock,
The sun drew in --
And stuck was Jim
Like a rusty pin...
But all in vain.
The clock struck one
And there was Jim
A little bit gone...

That is the child at the instant of reading the time travel novel, "a little bit gone." One foot in today and the rest stuck back in 1942 or 1857 or 1066. And though I have heard from at least one editor who feels time travel to be "a gimmick, a device, a framework" only, I believe it is a straight road into memory, an experimental act for an understanding of the past. It is once-upon-a-very-real-time, making history immediate and accessible for the young reader, letting them see backwards through a clear lens.

It is easier for a child caught between youth and adulthood to believe in layers of time that can be crossed or swum through or peeled away? Certainly it is easier than the simple memorization of rote fact. A ghost recalling personal history is more exciting than Mr. Devlin, my own children 's high school teacher at the blackboard, his chalk squeaking out dates. Kipling's Pook's Hills, where history is pressed together like the flowers between a book's pages, is more accessible than a text on British monarchies. And a boy in bluejeans asking his newfound friends why they are going on a crusade across thousands of miles voices the questions any sensible modern child would ask. The answers he receives are more palatable in a friend's mouth than the dry rota of a history professor.

Making history come alive is certainly one of the things that a time travel book can do. But so -- one may comfortably argue -- could a well-written textbook or historical novel. My counter to that is that children, while natural believers, are also natural cynics. They know what they know.

They will not easily believe, for example, that an intelligent person "knew" the world was flat. Maybe a little sister or brother not yet in nursery school, but not a grownup capable of ruling a kingdom or running a ship. So much for Queen Isabella and the good sailors of Columbus' time.

They know what they know. They will not easily believe that parents would allow their children to go on a hazardous journey across the Alps with only the company of other children. Not when they have trouble getting permission themselves to stay out an extra half hour on Saturday night. Not when Mom still packs a special bag for their overnight camping trips and Dad does a surreptitious drive-by around ten o'clock at night. So much for the Children's Crusade.

They know what they know. They cannot believe that real people killed men, women and children in a programmed and mechanical way, stripping their teeth for gold, using their hair to stuff mattresses, boiling down the body fat for soap, using their skin for lampshades, just because they were ordered to do so. This is not, after all, Friday the 13th, part 27, with catsup for blood and rubber prostheses. Eighth graders in a well regarded private school asked me, horrified, if I had made that stuff up. So much for the concentration camps.

They know what they know.

But take a book that starts in the real world and thrust a young reader back into the heart and mind of someone his or her own age forty of one hundred or a thousand years ago. Let that protagonist ask the questions ask the questions our young people all want to ask: how can you believe these Nazis when they say you are only being resettled? Because I, the protagonist (and therefore I, the child reader), am from the future and I know better.

The answers they get from the folk in the story will astound them, shake them into new awareness, really let them remember and be part of history. Not just "I remembered for the test" but "I know because I was there."

Rosemary Sutcliffe has written about her own reading of Kipling's Puck of Pook's Hill that it "linked the past of one corner of England with the present..." so that the child she was was made to feel it as a living and continuous process of which she was part.

"A living and continuous process." If time travel novels can be said to do any one thing, that is it: they take the past and make it a living and continuous process for the child. Children are mired in the present. They cannot see two weeks ahead in order to write their term paper early. They cannot see one year ahead in order to make realistic plans. If they are miserable today, they expect they will be miserable always. If they are happily content, they cannot believe in the possibility that such contentment should ever pass away. It is not death or poverty or fear that surprise them. It is tomorrow.

By taking a child out of that today in a novel, a child protagonist that the reader identifies fully with, and throwing the child backwards of forwards in time, the reader is too thrown into the slipstream of yesterday or tomorrow. The reader becomes part of that "living and continuous process," forced to acknowledge that we are our past just as we are our future.

I believe this so strongly that that when I was at last ready to confront what -- for any Jewish author -- has to be the most difficult and unrelieved period in history, the Holocaust, I knew that the only way I could write it was as a time travel novel. I am not sure I thought things through in logical steps. However, it came to me that it was the only way I could deal with the story I had to tell.

I wanted my readers to be unable to say, as the Indianapolis eighth graders had said, "Did you make this stuff up?" I wanted to throw them body and soul into that cauldron so that they would understand that it had been all but impossible to fight except to fight to stay alive. That within that hideous arena there existed not only hate but love, not only carelessness but caring, not only hopelessness but hope, and an abiding truth within careful catalogues of lies. I wanted my readers to remember as if they had been there, without having to come back to the 1980s with the long numbers scorched into their arms. I wanted them to remember. To witness.

The young protagonist I use as the reader's eyes and ears is myself, the child I had been; a little whiney, slightly uncomfortable in her own skin, able to make up stories on the spot, better with younger children than with girls her own age, often impatient, courageous without thinking though thought makes her afraid. A child who talks more than she thinks, who thinks more than she acts, but when she finally acts, is willing to go through with the action no matter what the consequences. I call her Hannah in America, but in the shtetl she is known as Chaya, my daughter's Hebrew name, a name which means life.

Hannah is the one who, when the wedding party going through the forest from one village to another comes upon truckloads of soldiers, shouts "They're Nazis. Nazis! Do you understand? They kill people. The killed... kill... will kill Jews. Hundreds of them. Thousands of them. Six million of them. I know. Don't ask me how I know. I just so. We have to turn the wagons around. We have to run." Just as any sensible child of today would say who knows a bit of history, who has seen Hogan's Heroes or any one of the many adventures starring Lee Marvin or Richard Burton kicking around the incompetent SS. What Hannah doesn't know, what the child reader doesn't know, is the reason why no one will take her advice. After all, the Jews didn't escape the Holocaust. And that. And that is the answer that the rabbi, father of the bride, who wants to comfort an hysterical child, gives her.

Shaking his head, he says" "There are not six million Jews in Poland, my child. And as for running -- where would we run to? God is everywhere. There will always be Nazis among us. No, my child, do not tremble before mere men. It is God before whom we must tremble. Only God. We will go ahead, just as we planned. After all, this is our shtetl, not theirs. And there is still a wedding to be made." He lifts his hand and on his signal the wagons start across the village marketplace towards the synagogue where the Nazis are waiting for them.

The lesson of history as we learn it in school is clear: the Jews did not run, the children of the crusades marched across the Alps into slavery. Columbus did not fall over the edge of his pride. We cannot change the past. But what few textbooks and history teachers can convince children of is why these people fell into pits, into prisons, into ambushes, into traps. We may look pack across our history books and shake our heads wisely, saying they shouldn't have. But, in fact, they did. We, in our turn, will do the same.

A living and continuous process. I hope the readers of The Devil's Arithmetic feel that. We say, forty years later, "Never again," yet it is happening again around the world: in Cambodia, in South America, in SouthAfrica, in Afghanistan, in Israel, in Ethiopia, on our own American city streets. Little pieces of the same kind of history with different characters and different names, but recognizable all the same.

Hannah tells her best friend Rifka when they are in the camp, "We should fight. We should go down fighting." After all, as a child of the 1980s, she knows about fighting. She's probably seen Rambo two or three times. It's on cable TV. But Rifka laughs.

"What would we fight with?"

"With guns."

"We have no guns."

"With knives."

"Where are our knives."

"With -- something."

Rifka put her arm around Hannah's shoulder. "Come. There is more work to be done."

"Work is not fighting."

"You want to be a hero, like Joshua at Jericho, like Samson against the Philistines." She smiled.

"I want to be a hero like..." Hannah though a minute, came up with nothing.

"Who?"

"I don't know."

"My mother said before she... died... that it is much harder to live this way and to die this way than to go out shooting. Much harder. Chaya, you are a hero. I am a hero." Rifka stared for a moment at the sky and the curling smoke. "We are all heroes here."

What Hannah learns, what the child reader learns, is that history is full of heroes. We are all heroes here. Maybe not like King Arthur. Or Robin Hood. Or Joshua at Jericho. Or Rambo. We are small heroes. That is, after all, what history is really about -- the small heroes. The ones who go across the mountains on faith and despite fear. The ones who get into a boat, believing the world is flat. The ones who gave their lives in the camps that others might live, and the ones who died in the camps just wanting to live another day.

We are all heroes here. Children need to know that was true back then and is true today. That it will be true tomorrow. It is a living and continuous process that they are part of.

The Devil's Arithmetic begins with the sentence "I'm tired of remembering" and ends with the words "I remember, I remember." Time travel books can give children back their memories by making history an experiential act.