AS WE KNOW IT A Father, a Family, and an Exceptional Child By Michael Berube Pantheon. 284 pp. $24

"Life as We Know It" is Michael Berube's eloquent, expanded argument on behalf of his son Jamie, who has Down syndrome. Berube is a professor at the University of Illinois and the author of three previous books, including "Higher Education Under Fire." In writing his own story, the author reaches out to include other families who have had children with Down syndrome. In reading it, one cannot escape the chilling conclusion that thousands of people have been grossly misunderstood, neglected and brutalized, not because of their mental limitations but because of ours.

Berube writes on behalf of all of these people, although it is Jamie whom he knows and loves. It is Jamie, too, who defies categories in his father's mind, even when the father tries to step back, in an exercise combining studied objectivity and parental anguish, and look at his child as others might see him:

"It never works. Jamie remains Jamie to me. I have even tried to imagine him as he would have been seen in other times, other places: This is a retarded child. And even This is a Mongoloid child. This makes for unbearable cognitive dissonance."

"Unbearable cognitive dissonance" is an apt term for the state of mind that may affect parents who have given birth to a disabled child. In the post-diagnosis atmosphere of shattered assumptions and altered plans, with an imagined future looming with emotional, financial and medical burdens, it is hard for any parent, however well intentioned or well educated, to know which way to turn. Some health professionals believe that parents with less education are more likely to achieve what the disability experts call "acceptance" than those who are highly educated. It is better, the thinking goes, not to think too much.

But why not, the author demands? Why not bring every last ounce of intellectual weight to bear on the issue of what it means to be truly human and to treat one another in a manner that is truly humane? This is exactly what Berube sets out to do. The task is not easy, for the author is in an ambiguous position. He is a writer, a scholar and a teacher, unquestionably intelligent. Yet to carry his point he must convince us that intelligence is not the proper measure of a human being. The book succeeds partly because Berube's arguments are brilliantly persuasive, but also because there is something irresistible about the arguer himself, wielding his brainpower like some action hero's light saber, in defense of a child who cannot (yet) defend himself.

Berube invokes philosophers and historians from Wittgenstein to Michel Foucault to John Rawls as he constructs a theory of social justice that depends on mutual communication among human beings, regardless of any hierarchy of "abilities." He researches and explains the dynamics of cell division that produce such anomalies as Down syndrome, citing evidence that this condition has been with us since Cro-Magnon times, "leavening the species with children who are somewhat slower, and usually somewhat gentler, than the rest of the human brood." He lays out the moral dilemma facing abortion-rights advocates who have had disabled children: Would they have chosen to have those children if they had known?

There is infinite compassion in the author's treatment of earlier parents, those who followed the advice given by medical experts of their day to institutionalize all Down syndrome children as "Mongoloid idiots" (a term still in common use as recently as 1971). Then he tells the story of Jason Kingsley, whose mother was given similar advice, rejected it and raised a boy who in 1994 co-authored a book refuting the stereotypes: "Count Us In: Growing Up With Down Syndrome."

The author admits that "there never has been a better time to be born with Down syndrome" -- thanks to antibiotics, modern surgery and changing attitudes as reflected by the Special Olympics and the popularity of Chris Burke, an actor with Down syndrome who starred in the television show "Life Goes On." Berube is deeply concerned about his son's future, nonetheless. He is not convinced that our society, with all its technical abilities to accommodate people like Jamie and allow them to thrive, has the commitment or the long-term will to do so. He fears that tightening fiscal policies may eventually force a vision of children with Down syndrome and other disabilities as "luxuries" society cannot afford to support.

At the living center of this discourse is James Lyon Berube, his story not obscured but, in some sense, protected by the compelling philosophical and social arguments his father has thrown around him like a warm jacket against a cold wind. Not insignificantly, there is a moment in this book when Jamie sees his father sleeping on the sofa, finds a blanket and brings it over to cover him. Fathers, families, exceptional children all, we are most human when we care for one another with the best we have to offer, as best we can. The reviewer has written several books for adults and children; he is working on a family memoir, "Under a Wing."