The campus is quiet in the late fall sun, a picturesque frieze of Gothic spires, golden trees and ambling kids in fleece and backpacks.

There are no more orange security barricades surrounding the small stucco building where Peter Singer teaches his weekly seminar, no more uniformed guards checking students' ID cards before unlocking the front door. No more demonstrators blocking the Princeton University administration building with their wheelchairs, screaming, "Princeton is where young Nazis go," getting carted off by the police.

Yet Singer, the Australian bioethicist and philosopher whose arrival sparked all that intense interest and protest as the semester began, is being cautious. Packages bearing unfamiliar return addresses go through an airport-style scanner before he opens them. Usually they contain only books, exactly what a professor would expect to receive, but some of the mail that greeted his arrival here was more menacing.

"Coming to America, I'm aware there is an element of the so-called right-to-life movement and Christian fundamentalism that's used violence," Singer observes in his quiet style. "Against doctors, for example." And his views on certain subjects, he goes on matter-of-factly, have made him "a sort of icon, a target, a demon if you will, for people to attack." So he keeps scanning.

American colleagues, accustomed to near-obscurity outside their classrooms and journals, can only rub their eyes in disbelief at Singer's flashbulb-illuminated entrance to Academe. "Name the last philosopher in the U.S. who's gotten this sort of attention," says Dale Jamieson of Carleton College, editor of a book of critical essays about Singer. "Philosophers go around the world saying fairly crazy things--'How do I really know that you exist?'--and nobody cares."

Not this philosopher. A specialist in ethics, he goes around the world saying things that start out sounding quite reasonable, derived from a utilitarian theory that dates to the 19th-century work of Jeremy Bentham and John Stuart Mill. Then his arguments take the next logical-seeming step and the next, winding up at positions that are startling, to say the least.

A few examples: Start with the utilitarian ideal that it is ethical to maximize pleasure in the world, and to minimize pain; to honor preferences rather than thwart them. Proceed to the principle that ethical decisions will give equal consideration to the interests of those affected by those decisions. Now, follow along:

If all creatures that are capable of suffering are entitled to have their interests considered, then it is wrong to eat their flesh. So we should all, ethically, become vegetarians.

If all persons should have their interests considered, then we are ethically obliged to send all the money we spend on luxuries to UNICEF and Oxfam to feed the starving--until we approach just-above-subsistence levels ourselves.

Or consider--and this is what brought antiabortion demonstrators and members of the anti-euthanasia group Not Dead Yet to the Princeton campus--Singer's thoughts on when it may not be wrong to kill an innocent human being.

If a human being is not conscious of self, not capable of rationality, not able to conceive of itself as an entity existing over time, then it is not, by Singer's definition, a person. Newborn infants lack those qualities, so they are not persons. If an infant is born with such severe disabilities that its parents and their doctors think its quality of life will be dismal, it is therefore ethical to painlessly kill it. In fact, even if a disability is not life-threatening, it can be ethical to kill a newborn if that allows a couple to then conceive a healthy child that would have a better life; that would maximize pleasure and minimize pain.

On the other hand, a terminally ill but lucid adult is a person, and if that person wishes to die quickly of lethal injection rather than slowly of stomach cancer, he should have that option.

Small wonder that controversy trails Singer like diesel fumes behind a city bus. He begins with the plausible and often concludes with the incendiary. He offends basic precepts of many of the world's major religions. He would permit actions currently illegal in virtually every state and country. He's been saying all this, and more, in rafts of books and articles and lectures for 25 years--but now he's saying them here, on a prestigious Ivy League campus within spitting distance of the world's major media encampment. He's in heavy demand as a speaker, on this campus and others; he's fielding constant calls from reporters; in between the usual round of faculty meetings, he's gotten used to photo sessions.

Of course that's one of the reasons he came. Singer has ambitions beyond academic colloquia: He wants to change millions of people's minds and actions. That's easier to do when the media are paying attention and probably easier to do in the United States. "It's a bigger pond than Australia is, and it's more globally significant," is his assessment. That it is also evidently more resistant to his positions hasn't dissuaded him. In Singer's brand of philosophy, "you keep close to the coal face"--going down into the mine, grappling with real-world problems, chipping away at the hard stuff a little at a time.

No Veils

Singer and his ideas are yet another development that can be blamed on the '60s, when a philosophical movement called practical ethics emerged to tackle the moral implications of everything from civil disobedience to suicide.

Singer encountered practical ethics as a graduate student at Oxford. "Suddenly there were new and significant topics, which made the idea of having a career in this area exciting," he recalls. "A career spent examining the meaning of words"--philosophy's dominant concern at the time--"was less appealing."

He is, in other words, a classic baby boomer, lanky and trim at 53 with wispy gray hair and glasses, wearing academic corduroy and a pair of chunky fake-leather shoes from Payless, home of animal-sparing synthetics. He and his wife, Renata, have settled on Manhattan's West Side; he spends four days a week on campus, then Amtraks home. Their three daughters are university students in Australia.

Princeton has been quick to defend him against demands that his appointment be rescinded, even when one of its own trustees, would-be presidential nominee Steve Forbes, very publicly announced he would withhold all contributions from his alma mater in protest. But it has been slower to provide him with bookshelves, so his office at the Center for Human Values is still starkly bare-walled, stacked with cartons shipped from Melbourne. There's a campus map taped to a file cabinet to help the new prof navigate his surroundings.

The prof, it should be noted, has a calm, noncombative demeanor and a quiet voice with a broad Australian accent ("faaam animals") and will certainly disappoint anyone expecting a firebrand. The seminar he's just finished leading is by all accounts a model of civility. Though he's frequently described as one of the world's most influential philosophers, students find his intellectual rigor daunting but his personal manner unintimidating. "I get asked a lot, 'What's it like in there? What's he teaching you?' " says one undergraduate. "And he hardly 'teaches' at all; he talks maybe 1 or 2 percent of the time, as a moderator. It's a discussion." The seminar's title, "Questions of Life and Death," may be the most dramatic thing about it.

Yet the prof knows that he is provocative; he intends to be. Sometimes an activist himself, he has demonstrated against the mistreatment of hens by hunching in a too-small cage in downtown Melbourne; he was twice an unsuccessful Green Party candidate for Parliament.

Princeton students, professors and administrators, closing ranks in support of academic freedom, say they welcome his iconoclasm. "It is not productive to allow oneself to be so horrified by an issue that one is not willing to face up to a rigorous discussion about it," says Jon Steinson, an economics major taking Singer's seminar. "That is what we are trying to do."

In fact, a few people have countered Forbes's action by sending Princeton checks--small ones, though--to support Singer's appointment. "Where else but at a university can people express morally serious views that are deeply challenging to many of our presuppositions?" says Amy Gutmann, director of the Center for Human Values.

When his fellow academics try to explain why he's in the spotlight when others who've espoused similar positions (and there are a number) remain largely unknown, they come up with several plausible explanations. Singer is extremely prolific, for instance. "He's published enough for four or five people," notes Princeton philosopher Gilbert Harman, and his books have impact: "Animal Liberation," which can fairly be said to have launched the animal rights movement in 1975, has sold more than 400,000 copies in 11 languages, while "Practical Ethics" has remained in print for 20 years.

Singer's prose style--clear, accessible, blunt--helps, too. Readers won't catch him talking about "letting nature take its course" when he means "allowing to die" or "killing." "I don't want people to glide past these issues on euphemisms," Singer says. "If you put up all these veils, people don't see what's at stake."

He further suspects, as do both supporters and critics, that his appointment provided a convenient way for people with certain political agendas to seize the spotlight. "He becomes the whipping boy for nutty-academia-out-of-control and the ongoing debate about abortion," says Arthur Caplan, who directs the University of Pennsylvania Center of Bioethics. "Singer was turned into a political cause."

Some of his views are less than headline-grabbing, of course. In the years since he published "Animal Liberation," and gave his early royalties to fledgling groups like People for the Ethical Treatment of Animals, he and they have had some impact on the use and treatment of research and farm animals in Europe. Even in this country, "if you walk into a shop and pick up cosmetics or shampoo, it will almost certainly say 'Not Tested on Animals' and that claim will probably be true," Singer says.

Meanwhile, those unmoved by his contention that refusing to consider animals' interests is mere bigotry, "species-ism" akin to racism, don't mount demonstrations. They merely ignore Singer, a committed vegetarian since graduate school, and go their hamburger-eating ways.

Nor has Singer gotten much public flak for urging affluent Westerners to give far more to international relief organizations. "It's pretty hard for people to protest against suggestions that we ought to be more generous towards the poorest people in the world," he notes dryly. In fact, a piece he wrote in the New York Times Magazine in September resulted in donations of $75,000 to Oxfam America and thousands more to UNICEF. Singer himself gives 20 percent of his income to such charities, which he acknowledges is considerably less than he should by his own arguments ("It's something you work on").

When his critics take issue, they focus on his stringency--his Times call to arms identified $30,000 as the amount of household income Americans need to spend on necessities annually, so that a morally decent family bringing in $50,000 owes UNICEF $20,000. "In theory he's right about that," says NYU philosopher Peter Unger. "But most of the time it's counterproductive. People say, 'That's ridiculous, it's just too hard' " and do nothing. Critics also debate the economic consequences of everyone following Singer's advice. But it is advice that's easy, Singer sadly agrees, to ignore.

The groups too infuriated to shrug at what Singer says--or what they think he says--are antiabortion advocates and disability activists. "If he were a madman raving on the corner, you could ignore him," says Nancy Weiss, executive director of TASH, a Baltimore-based advocacy group for the disabled. "But he's a sanctioned academic, and that's scary."

Personhood

In the '80s Singer turned his attention to medical ethics, a field he considered full of sloppy thinking, and was the first president of the International Association of Bioethics. He thinks abortion and voluntary euthanasia should be legal, which doesn't make him unusual among bioethicists, and that infanticide should be in certain cases, which does.

It all seems perfectly logical to him. Society already supports the right of parents and doctors to decide, if prenatal testing detects diseases or handicaps, that a fetus should be aborted. Why should that right end at birth? In hospitals around the world, certain disabled newborns are already quietly allowed to die without aggressive medical treatment. Why is that better than a swift, painless death? "There is no ethical gain by simply not operating on those you've decided should die, waiting for them to get some infection or hydrocephalus so they die over a period of months, perhaps," he argues.

None of this applies to rational, self-conscious people with disabilities, in Singer's philosophy. It's ethical only for newborns, who are not "persons" by his definition, or for those at the end of life capable of making their wishes known. For disability activists to ignore these distinctions is "grotesque," Singer charges, and "conjures up the vision of my going after these people in their wheelchairs and saying, 'You ought to be killed.' "

But the disabled are not appeased by his distinctions. They think his ignorance about disability leads him to condemn afflicted infants who could nevertheless have good lives. Singer would permit infanticide in severe cases of spina bifida, for instance, which can cause paralysis, lack of bowel and bladder control, and mental retardation. "Want me to give you a list of people having perfectly reasonable lives with paralysis, incontinence and intellectual disabilities?" counters Adrienne Asch, a Wellesley College bioethicist who debated Singer at Princeton. "They have friends, they work, they travel."

The disabled may put less faith in physicians' predictions than Singer does. They also invoke the so-called slippery slope: If society agrees to kill some disabled newborns, why wouldn't it then target others deemed a burden? Why wouldn't it stop working to accommodate the disabled, with everything from wheelchair ramps to special-ed programs, and simply eliminate them?

Most of all, they take vehement exception to Singer's core idea that some human beings are persons and some are not. At a time when access to health care and protection from discrimination are being wrangled over in legislatures and courts, the specter of nonpersonhood is not only insulting, but frightening.

"All humans should be regarded as persons," says Stephen Drake of Not Dead Yet, who demonstrated at Princeton this fall. "Many cultures went down the road of classifying certain individuals as nonpersons; it's always associated with oppression and victimization."

Singer says he probably wouldn't have chosen this particular question as the source of his demi-celebrity in America; some of his colleagues feel the same way. Listening to Singer on bioethics, "maybe the public will assume that that's the way everybody does it," says Thomas Murray, president of the Hastings Center, a bioethics think tank. "I grimace a bit when I think of that possibility."

For his part Singer, raised in a Jewish home where the Holocaust cast a long shadow (his parents escaped Austria in 1938, but three of his grandparents died in concentration camps), the charges that he's some sort of Nazi are particularly abhorrent.

But they don't disprove his theory, of course. "Do I believe that you can have legal euthanasia without any abuses?" he asks coolly. "No. Do I believe you can have legal euthanasia without more abuses than we already have? Yes."

The Unsayable

Left unanswered, now that editorial-page denunciations have yielded to academic routines, is how much influence Singer can muster here.

A few weeks ago, submitting to a radio talk show, Singer was explaining his theories when a listener called to demand, "Are you saying that you're an atheist?" Singer replied that he was, "and I didn't see anything particularly remarkable about it." Though raised in a home that was culturally Jewish if not religiously observant, Singer decided in his teens that the merciful God he kept hearing about didn't square with the misery he observed.

Perhaps that's why he may not have grasped the still-significant role religion plays in politics here. "I've seen all the statistics about how many Americans go to church and believe in God and don't believe in evolution," he says, calling those numbers "pretty startling" to outlanders. "But I guess I underestimated the extent to which that dominates public rhetoric."

His style, bold on the printed page but dispassionate when he's behind a microphone, may also prevent household-name status. "He's not a boisterous, bombastic enough figure to show up on 'Crossfire,' " says Caplan. Perhaps the disabled, and the poultry producers, have little to fear.

Yet those who think that thorny bioethical issues deserve more open discussion, not less, need not worry that Singer will shut up and slink away. "He's a very secure person, which is unusual in academic life," says Jamieson. "He believes strongly in what he does, has a strong ego."

This is a man who regularly says the unpalatable, the usually unsayable. That there is no inherent "sanctity of human life," for example. Or that "the collapse of our traditional ethics," the subtitle of one of his books, is actually a positive development. He listens respectfully to his critics, sometimes tweaks his opinions, but hasn't fundamentally changed his mind about his theories in 25 years.

Even the sorrowful condition of his 91-year-old mother, a retired physician who after several years of Alzheimer's disease can no longer complete a sentence, doesn't shake his convictions. Those poking for evidence of hypocrisy, holes in his logic, point to the way Singer and his sister support her, paying for her round-the-clock care. If he believes everything he says, why doesn't he just kill his mother, who may no longer fit his definition of a person?

"If she were in pain and distress and suffering, than I think the issue of euthanasia would clearly arise," Singer responds, calmly as always, reasoning it through. "One question is whether she would have wanted to go on living like this. Maybe she wouldn't; that does trouble me. But that would have been a decision for her to make, and she never really made it. She was never in a state where she was aware she was getting Alzheimer's . . . yet competent to say what she'd want." At times, he has regretted being public about her illness, but it has not convinced him that he is mistaken. Or that he should strive for tactful inoffensiveness.

Singer was among a few dozen heavyweight scientists and scholars weighing in at a Columbia University conference last month on the "State of the Planet," held in the soaring neoclassical rotunda of Low Library. During a break between sessions, a middle-age man who called himself "a budding theologian" politely came up carrying a few questions jotted on a torn-out notebook page. He was wondering, among other things, how Singer regarded "Judeo-Christian thinking."

The philosopher hesitated for no more than five seconds. "It contains some advances and some flaws," Singer told him. "I wouldn't want to say it's the best ethical statement that could be made. I'm not an uncritical fan of the Judeo-Christian ethic."

CAPTION: "I don't want people to glide past these issues on euphemisms," ethicist Peter Singer says. "If you put up all these veils, people don't see what's at stake."

CAPTION: Daniel Robert of New York and other advocates for the disabled picketed Princeton University in April over its appointment of Peter Singer.

CAPTION: Academia has meant anything but obscurity for bioethicist Peter Singer, who notes that his ideas have made him "a sort of icon, a target, a demon if you will, for people to attack."