BOOK REVIEW : Bringing Fuzzy Logic Into Focus : FUZZY LOGIC: The Discovery of a Revolutionary Computer Technology--And How It Is Changing Our World by Daniel McNeill and Paul Freiberger Simon & Schuster:$22; 319 pages

We often say that two things are as different as night and day, by which we mean that they are very different indeed. We know what night is, and we know what day is, and we can easily tell them apart.

But what about twilight? Is it night or is it day? Hmmm. Well, it’s a little of both. What’s more, though we know the difference between night and day, it’s hard to pinpoint the moment when one ends and the other begins.

Since the time of the ancient Greeks, Western thought has focused on the clear-cut distinctions in the world, the nights and days, and paid scant attention to the twilights.

One of the basic tenets of formal logic is that a statement is either true or not true. It can’t be both at the same time. Modern computers embody this idea. A switch is either on or off, 1 or 0. Nothing in between.

But while this sharp distinction between true and not true may be good for formal logic, it does not accurately reflect the world in which we live, which is riddled with maybes. Is a certain friend reliable? It depends. Should one always tell the truth? Usually, but once again, it depends. When should you buy a stock, and when should you sell it? No one knows for sure.

The vagueness inherent in the real world is the central insight behind the field called “fuzzy logic,” which is an effort to get computers to deal with shades of truth. Created by Lotfi Zadeh, a Berkeley engineer, in the mid-1960s, fuzzy logic has traveled a bumpy road in the years since.

It has been alternately hailed as the be-all and end-all of computers and machine control and derided as a mere fad--or worse, a hoax, no different from astrology. “Fuzzy Logic” by Daniel McNeill and Paul Freiberger is in the be-all, end-all camp.

McNeill and Freiberger, who are popular science writers, do a good job explaining what fuzzy logic is and profiling some of the key people in the field. They also show how fuzzy logic has been adopted in Japan, where “fuzzy” is a big selling point for consumer products such as washing machines and vacuum cleaners.

To be sure, the authors give voice to the skeptics who scoff at fuzzy logic. But overwhelmingly, this book argues that the skeptics are wrong, and that it is only the pigheadedness and shortsightedness of Americans that has kept fuzzy logic from making important contributions in the United States.

Just as Western thought is based on crisp distinctions between black and white, yes and no, true and false, the authors say that Eastern thought is much more sensitive to vagueness. “Wisdom lies in paradox,” they say, and they quote Bart Kosko, a USC Wunderkind who is a leader in the field, who says, “My claim is that Buddha was really the world’s first fuzzy theorist.”

This explains, they claim, why the Japanese have embraced fuzzy logic while the West has not.

Along the way, McNeill and Freiberger draw a very good picture of the sociology of science: Because fuzzy logic has not had many prestigious adherents in this country, it is hard for its researchers to get grants and to have their papers published in learned journals.

Of course, academic leaders would say that they are doing exactly what they should do. They are not being irrational or spiteful. Rather, they are using their best judgment to decide what work is promising and what work is not.

Nonetheless, all researchers with a novel idea who are turned down for a grant claim that they are like Galileo or Pasteur. Alas, Galileo and Pasteur are the exception and not the norm.

“Fuzzy Logic” draws attention to an interesting and potentially useful field of study. But McNeill and Freiberger would have written a better book if they had taken a more evenhanded approach.

They recognize that “overhype is a real danger to nascent technology,” but they commit the sin of overhype, starting with the book’s subtitle: “The Discovery of a Revolutionary Computer Technology--And How It Is Changing Our World.”

They allow Kosko and others to make extravagant claims for fuzzy logic, essentially uncontested. Kosko says, for example, that fuzzy logic will enable computers to routinely write novels. “A computer might not pop out a thriller every day,” they say, “but perhaps once a week or month. (Kosko) predicts such a power within 20 years, and perhaps some form of it sooner.”

He should live so long.