By David K. Johnson, Ph.D., King’s College
Abortion is a controversial issue. There are a few points that academics on both sides make that are important to fully understand this issue. Though we are not looking to settle the argument here, the ideas of personhood that are raised while discussing the ethics of abortion are useful.

Fetal Personhood
Academics generally agree that there is no way to determine, scientifically or philosophically, when “personhood” begins. One could say it’s when fertilization is complete; when you have a cell, a zygote, with a new unique genome. But that’s just an assumption; that’s technically true of cancer cells—but they’re clearly not persons; and most of the material in the zygote will end up being the placenta.
You might argue personhood begins when God puts “a soul” into the fetus, but we can’t even establish scientifically or philosophically that adult humans have souls. So that’s another dead end.
Maybe personhood begins when mental activity begins. But the brain activity of a fetus increases gradually—there is no definite point when it begins; and not all parts of the brain produce consciousness, and we don’t fully understand how it’s produced. So there’s no way to know when a brain’s activity has become sophisticated enough to produce a mind. It could even be after birth.
This is a transcript from the video series Sci-Phi: Science Fiction as Philosophy. Watch it now, on Wondrium.
The Future Hypothesis
The most famous academic papers on abortion refrain from basing their argument on fetal personhood, because they see it as irrelevant. Take the pro-life philosopher Don Marquis. He argues that, even if a fetus is not a person, abortion is still immoral. Abortion is wrong, Marquis argues, because even if a fetus isn’t a person, it could have a “future like ours”.
As evidence of this, suppose you heard a news story about a fatal accident involving a bus filled with elderly tourists. You would, of course, think this is a horrendous moral tragedy. But suppose you later learned the bus was filled with 1st graders? You would think that it is a much worse tragedy. But why?
Marquis argues that we react this way because the children had more of their future ahead of them; the death of a young child prevents the occurrence of far more future experiences than the death of an elderly person. When it comes to the morality of killing, what matters most is how many quality future experiences were never had.
Learn more about personal identity.
The Right to One’s Body
On the flip side, philosopher Judith Thomson also agrees that fetus personhood is irrelevant, but she comes to the opposite conclusion. Thomson grants, for the sake of argument, that a fetus is a person, right from the moment of fertilization. So abortion is an act of killing. Despite this, she argues, abortion can still be and often is morally acceptable—just like killing in self-defense can be.
The crux of her argument relies on the common idea that persons have a fundamental right to use their own body or its parts as they see fit. Indeed, Thomson argues, this right outweighs any other person’s right to life.
The Question of Moral Obligation

Thomson imagines a sci-fi like scenario in which you have been kidnaped by fans of a famous violinist; you awake to find that they have plugged his bloodstream into your kidneys, by means of some futuristic device, to keep him alive. It will take 9 months for his body to heal, and if you unhook yourself, he will die.
Thomson observes that everyone would agree that you are not morally obligated to stay tethered to the violinist. You have a right to use your body as you please, even if it would cost someone else his life.
And it’s for this reason, Thomson argues, that a mother can terminate a pregnancy, if she so chooses, even if a fetus is a person. A mother has just as much a right to use her uterus as she sees fit as you do to use your kidney as you see fit—even if it will cost someone else’s life.
The Risk and Responsibility
When a woman gets pregnant, it’s usually at least partially the mother’s responsibility. So one might argue that, since the mother knew pregnancy was a possible outcome of having sex, she is morally obligated to carry the fetus to term. It is a moral rule: When one knowingly takes a risk, one has to pay for the consequences of one’s actions—especially when that risk endangers others.
But others will argue that this actually isn’t a moral rule. Suppose you get into a two-car accident on the interstate. Now, an accident is always a possibility. And you could have taken the side roads, but didn’t. Would you be obligated to give the other driver your kidney if he needed it to survive?
Learn more about the ethics of reproduction.
Recklessness and Morality
Notice that the answer likely turns on how safe you were while driving. Were you going 20 over the speed limit and weaving in and out of traffic? Then yes, you probably do owe him your kidney; you were being reckless. Were you driving within the speed limit, in the right lane, with your hands at 10 and 2—then you probably don’t, because you were being careful. So is having sex more like driving recklessly—something for which one should have to pay the consequences? Or is it more like driving responsibly, something one should be able to do without giving up their rights in the case of an accident?
Your answer to that last question likely boils down to your views about the morality of sex. So instead of being generated by different assumptions about whether a fetus is a person, maybe the widely divergent answers on the abortion question come from different assumptions about the morality of sex.
Common Questions about Personhood and the Morality of Abortion
Don Marquis argues that abortion is wrong, because even if a fetus isn’t a person, it could have a future life, like ours.
Judith Thompson’s argument relies on the common idea that persons have a fundamental right to use their own body or its parts as they see fit. It’s for this reason, Thomson argues, that a mother can terminate a pregnancy, if she so chooses, even if a fetus is a person.
Instead of being generated by different assumptions about whether a fetus is a person, maybe the widely divergent answers on the abortion question come from different assumptions about the morality of sex.