John: I would be delighted to adopt the portions of your consensus proposal that protect human beings’ right to life while continuing to argue over the other portions of it. I take it that your proposal would prohibit second- and third-trimester abortions at the very least—so we’ll have to get the Supreme Court to back off a little before we can implement your proposal. Your proposal will also close the door to those bioethicists who want to use cerebral death as the criterion for death, so that organs can be harvested when the cerebrum is gone.

As for the other aspects of your proposal: You are correct to say that it is sometimes necessary to draw arbitrary lines—take, for example, the age of majority. But I am not sure that we need to draw a line between those human beings whom we consider it wrong to kill and those we consider it okay to kill. (I do not, by the way, think that the mere ability to perform “some kind of living functions” meets valid criteria for life; you might be able to see my actual point more easily if you think of an organism as a biological entity that can organize itself and its own functioning). My reasoning in rejecting the category of the human non-person—which can be found in the middle of this article: http://www.hooverdigest.org/044/ponnuru.html–is not based on a belief that those beings who would be consigned to it (such as embryonic human beings) have souls; my own church does not have a settled doctrine on this question, and I don’t think a conclusion in the matter is necessary to reject the killing of human beings.

Your concluding thought is that the protection of these living human beings “cannot be accomplished”—I assume you mean something like “justified” or “defended” here—”purely on medical, legal, and natural-rights grounds, because they offer no legally enforceable guidance about the existence and nature of the soul.” But it is not as though the state protects you or me from being killed because it recognizes that we have souls.

I think your proposal trades on an ambiguity. If you want the possibility of thought to be the criterion, then the presence of detectable brain activity will be an overinclusive measure. But if you want to chuck that measure and go with some other measure of thought, then you can’t avoid consequences that I think you would like to avoid (such as justifying infanticide).

You write that most civilized people draw the same line you do, between those human beings who might have the ability to think and those who do not. It is not at all clear to me that this is true. I think a number of objections can be raised to that thesis, but to pick just one: If it were true, why does the law generally prohibit the killing of human beings whose cerebrums are gone but whose whole brains have not died? (Why, for that matter, are we allowed to kill animals with more cognitive ability than severely retarded human beings whom we are not allowed to kill? Once mere membership in the human species is no longer a criterion of worth, I think it is hard to resist the logical pull of Peter Singer-land.)