The landmark Roe v. Wade decision, handed down by the United States Supreme Court in 1973, touched off a divide deep within the American culture that shows little signs of healing. The reason is not necessarily that people have intransigent views when it comes to abortion. Instead, the issue is genuinely hard to grapple with, even from a moral standpoint, as Harvard Law Professor and bioethicist Glenn Cohen explains.

The first question we face when deciding whether abortion is immoral is this: are fetuses persons? That may seem like a straightforward question, but determining personhood requires understanding the distinction between a person, a human being, and being alive.

Certainly not all things that are alive are persons. A dog, for example, is very much alive and very lovable indeed, but not a person. As simple as this distinction seems, it has its detractors. The philosopher Peter Singer, for example, says that distinguishing between what is human life and inhuman life is an example of speciation — an act of discrimination that is ultimately logically untenable (and we should therefore abandon it).

According to Cohen, some scholars say that stem cells and embryos are human beings, but not persons. They are made of human being stuff but they do not have the moral and legal rights — namely, the right of inviolability — that we accord to individual persons.

Those who believe the granting of rights is more a political act than a natural one may look toward what Cohen calls a “capacity ‘x’,” i.e. some other quality that more accurately defines what a person truly is. Examples of such a capacity ‘x’ include experiencing a continuity of identity, or possessing self-knowledge. While these qualities form more naturally than the granting of political rights, they open the door to difficult-to-justify actions like infanticide (since the infant brain is insufficiently developed to have the concept of an identity, or to articulate self-knowledge).

If one decides to stick with a definition of “person” that is determined by the existence of moral and legal rights, thinkers such as Judith Jarvis Thomson point out that the rights of a mother countervail — she is a person, too, after all. Thomson’s famous thought experiment, “the famous violinist” has become perhaps the most recognizable philosophical defense of abortion.

Glenn Cohen’s book is Patients with Passports: Medical Tourism, Law, and Ethics.

Glenn Cohen:  In the 1970s we have the Roe v. Wade decision in the United States. It was a decision relating to a woman's right to have an abortion. It introduced the trimester framework. It basically allowed first trimester abortions, made it very difficult to have third trimester abortions. And essentially this was really met very quickly thereafter with the sort of backlash. And really the last 40/50 years of American history have more or less been a backlash against Roe v. Wade and an attempt to kind of criminalize abortion in all sorts of interesting ways without overturning the decision.

So that's kind of the legal playing field. I mean we can talk about some of the specifics, but the more interesting question I think is thinking about the morality of abortion. And I'll say that I think abortion is an extremely difficult question. So one of the first questions people have to think about is are fetuses persons? And that's a very important linguistic question, persons. I didn't say human beings. I didn't say alive. Those are three different issues. Something can be alive but not be a person. Your dog is a good example. You love your dog. It's a wonderful thing but it's not a person. Something can be human and potentially not be a person. Some people think the embryo, for example, before 14 days or stem cells being derived are members of the human species but may not be a person. So what do we mean by persons? We mean something that has a certain set of moral and/or legal rights, most important of which is a right against in viability. They can't be killed or destroyed or harmed without very good reason. And we have the attitude that we're all persons so we have an index case we're pretty clear we're persons and the question is who else is a person? Well to answer that you need to have a theory about what makes something a person.

And there are a few different kinds of theories you can have. One could be just to say if X is living and a human being X is a person. Now some people have problems with that. So Peter Singer and some animal rights advocates, for example, think that that's a speciesist attitude, that by saying human equals person it's problematic that we're excluding animals. Instead we ought to have some criteria that looks at capacity. So other people have sometimes what are called a capacity X view where they say in order to be a person you have to have X capacity and then we have to fill in what X is. Is it the ability to think complex thoughts, the ability to plan and look towards the future, the ability to feel pain whether you understand it? Is about continuity of an identity over time or is it merely being alive and breathing? And some people think it's a single criteria, others think it's a compound criteria. And then there are complex questions about what happens for things that have the potential to have capacity X or had a capacity X but lost it.
So, for example, a fetus doesn't have the abilities, early fetus let's just say an embryo just to make it very easy, an embryo before 14 days doesn't have the capacity to think deep thoughts about the future or have future orientation. I think that's pretty well accepted by everyone, but it certainly has the potential to do so. And the question is is that enough? What kind of theory or potentiality? Hydrogen and oxygen each have the potential together to become water. Does that mean that they are water? They have the metaphysical properties of water. Or do we require more of a kind of a potentiality something like in the natural course of things they will become something?

The other difficult set of categories are things that once had the capacity but now no longer have and perhaps never will again. So those that are brain-dead, for example, are a good example. They are certainly human beings. Most cases they have been persons. But now if your capacity for personhood how do you define personhood is something like the capacity to think deep thoughts about the future or do you have future orientation, these are entities that no longer have that capacity and we don't believe will have it again. Do they cease being persons at that point? Let's just say that in order to understand whether a fetus or an early embryo, the kind that are used for stem cell derivation, is a person. You have to do a lot of metaphysical work in understanding what makes something a person and why and what those capacities are.

Now even if you think something is a person that doesn't necessarily mean you've solved the abortion problem. So it's possible, although popular among philosophers not so popular in the political process, to say fetuses are persons and yet abortion is still legal and justified. How does that argument go? The suggestion is that there is a right of another entity that has overcome whatever interest the fetus has and that is the right particularly of the mother who is gestating the fetus. So they claim is yes a fetus is a person. Yes abortion will cause the death of a person. But that doesn't mean that abortion is wrong because a woman gestating the fetus has a right to stop that gestating, even if it will result in the death of a person. And the most famous versions of this argument comes from Judith Jarvis Thompson, a very famous I thought experiment about the worlds most famous violinist. And she says imagine you find yourself a heavy night of drinking; you got drunk; you blacked out and you wake up the next morning and you find yourself a human dialysis machine hooked up to the world's most famous violinist. Nobody doubts the violinist is a person. He's not only a person, a great person, the world's most famous violinist. But she says don't you have the right to unplug yourself from that person even if it will turn out that it will result in the death of the violinist? And she says if you think the answer is yes then you think that even though the entity is a person you may have a right to cause its death, a right to unplug itself. And she analogizes that to the right of a mother to unplug herself from her fetus who is a person.

Now there's lots of contestation about that thought experiment. You might say you got drunk no fault of your own somebody kidnap you. Is that really the situation of all women who become pregnant or is it the situation only of women, for example, who are raped or who are impregnated in an unconscious state? But this is just to show that there's some complexity.
Okay, one more point. That is that the stem cell question looks different on in this regard. Remember when we we're talking about embryos we're talking about embryos that are frozen that are in a lab. Nobody is gestating them. If embryos have the rights of persons, unlike in the case of abortion because nobody has a contrary right to stop gestating them, so you might actually think the argument for prohibition against destroying early embryos is easier than the argument or prohibiting abortion for this reason. Now, on the flipside you might think the early embryos have even less of the capacity X, whatever that is, than does the fetus. But this is the way in which bioethicists and lawyers think about these problems.