Special To The Commentator:

I have read with interest Rabbi Tendler's critique of the views expressed in my new book Practical Ethics. It seems as though Tendler conveniently selected a few choice phrases, but didn't bother to react to my actual argument. So allow me to explain why it is not always wrong to take the life of an innocent human being.

We tend to take many things for granted, and the idea that it is always wrong to take the life of an innocent human being is something that we scarcely dare question. Yet philosophers ought to question just those beliefs that we routinely take for granted, including this one.

Here is one way to look at this problem. Ask yourself: Is it worse to kill a human than it is to kill, say, a chicken? Unless you are a vegetarian, you are certainly going to say yes, it is. And even if you are a vegetarian - as I am - you are very likely going to think - as I do - that when someone kills people randomly in a church or school, it is a greater tragedy than that which happens daily at a slaughterhouse. But why? Unless we take refuge in religious teachings, which not all of us share, the answer must be because of some difference between humans and animals. That difference, however, cannot merely be the fact that we belong to one species, and chickens, for instance, belong to another. To think that mere species membership alone could make such a crucial moral difference would be a kind of species-racism - more briefly, speciesism. Suppose there were intelligent Martians, very like us, and entirely peaceable and friendly to us, but of a different species. Would it be acceptable to kill them just because they are not members of our species? Surely not.

So if it is worse to kill human beings at random than to kill nonhuman animals, the difference must lie in kinds of beings that humans are. And I would suggest, more specifically, that it must have something to do with the higher mental capacities that humans have - capacities that nonhuman animals do not have. I am not merely referring to the capacity to feel pleasure or pain, or to suffer from the severing of a relationship like that between mother and child, for all mammals have these capacities. To give us a reason for thinking it worse to kill typical humans than it is to kill beings of other species, the capacities must go beyond these. They might include not merely awareness, but self-awareness, or possibly the capacity for making plans for the future. Here we have, I believe, a reason for distinguishing between the wrongness of killing beings that is based on something that is clearly morally relevant. The fact that a being is capable of understanding that it has "a life" does make it worse, other things being equal, to end that life. Then, and only then, are we ending the life of a being that knows it is alive, and can see itself as existing over time. Then, and only then, does the being have any conception of what it might lose by being killed, or have any desires for the future that are thwarted by being killed.

But at this point it will become obvious that while typical humans - the humans who get killed when a gunman randomly fires into a crowd - have these capacities, and have them to a degree that a nonhuman animal does not, some humans do not have them. Newborn infants, for example, do not have them. And, while you might immediately object that a newborn infant has the potential to become a being with intellectual capacities far superior to that of any nonhuman animal, if this is supposed to be the reason why it is as bad to kill a newborn infant as an older human being, we shall have to acknowledge that the human fetus also has a very similar potential to that of the infant, and hence the same reason would make it very seriously wrong to kill a human fetus.

Some of you, of course, will endorse this conclusion. But let us note here that a lot of people do not, and without the influence of religion, the foundation upon which Rabbi Tendler based his column, even fewer would endorse it.

I do not think that the potential of a being is enough to make it wrong to kill that being. As it happens, just today the United Nations estimates that the world population will pass six billion. It appears to be heading for somewhere around 9 or 10 billion - a figure that will strain our planet's resources to the limits of their capacity. Most people do not think it obligatory, or even desirable, for fertile couples to bring as many human beings as possible into existence, even though each one of them would, in all probability, become a unique, rational, self-aware human being. And on the same grounds, I do not think the fact that a human fetus would, in all probability, become a unique, rational, self-aware being is a reason against having an abortion.

For the reasons I have just quickly sketched, I do not think that killing any newborn infant is morally equivalent to killing a rational and self-conscious being. This does not mean, of course, that killing infants is a matter of moral indifference. On the contrary, to kill an infant is normally very wrong indeed, but normally it is wrong primarily because of the harm it does to the parents, who have conceived the child, and already love it and wish to nurture it. The death of a newborn infant is generally a tragedy for the parents, not for the infant who has not even glimpsed the prospects of the life that might have been in store for it. But there are circumstances, when an infant is born with a severe disability, when parents think that it would be better for the child, for themselves, and for their existing children, if the newborn infant did not live.

Last month I received an email from Mr. H. of Connecticut. He wrote as follows:

As the father of a severely handicapped child, I agree with you. He suffers from seizures every day, but the catholic hospital that used extraordinary measures to keep his 24 week gestation, one pound body alive without parental input does not care about him today. They got to "play" with their toys six years ago, and leave my family with the burden and David with the daily pain.

Don't let the fanatics get to you. They could never deal with our burden, or suffer through David's pain.

And here is another message I received, from a woman I will call Mrs. B.:

My son, John [not his real name], was born almost 2 1/2 years ago 11 weeks premature and weighing only 1 lb. 14oz. They assured me that because he was already 29 weeks and had no intracrainial hemorrhages that he would be fine; he would just need to catch up with other kids his birth age. That is not the case. John has spastic diplegia cerebral palsy with underlying right hemiplegia…has sensory problems, and has speech delays. We don't know what his level of intellectual functioning will be, although people tell me he will probably be of "normal" intelligence with perhaps numerous learning disabilities. He is certainly more functional than some children with CP and has at least a small chance at a reasonably "normal" life, but that is not the issue.

My husband and I love our son (middle of three), but had someone told me, "Mrs. B. your son will have numerous disabilities down the road. Do you still want us to intubate him?" my answer would have been "no." It would have been a gut wrenching decision, but it would have been in the best interest for John, for us, and for our other children. I am saddened beyond words to think of all he will have to cope with as he grows older.

I do not think that Mr. H. or Mrs. B. are atypical parents. They live with children with severe disabilities, and they clearly judge the lives of their children to be such that it would have been better if they had died at or soon after birth.

In those circumstances, some doctors will allow the infant to die by withholding treatment. People seem to accept this kind of "passive euthanasia." But if the parents and doctors reach that decision, why allow the infant to suffer any longer than necessary? I do not see that it is better to deliberately allow an infant to die slowly, than to kill it painlessly.

Dr. Peter Singer is the DeCamp Professor of BioEthics at Princeton University, and the author of Practical Ethics.