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In most states, young people can drive a car at sixteen. At eighteen, they can vote and serve in the military. At twenty-one, they can drink alcohol. At twenty-five, they can serve in the House of Representatives; at thirty, in the Senate; and, at thirty-five, as president of the United States. We gain rights as we age. So too, hold some of the most influential philosophers of the day, with the unborn. The child just conceived has no right to live, but one ready to be born does. The right to life is a right one attains sometime between conception and birth.

“The further along the path toward being born a fetus has progressed, the more protection we feel it should have from being destroyed, and the more urgent the need for abortion needs to be (for example, that the life of the mother is at stake),” observes a leading English philosopher Mary Warnock in her book An Intelligent Person’s Guide to Ethics. “Very few people would argue that there is no difference between the decision to abort at six weeks and the decision to do so when the fetus would be viable outside of the womb, which today is generally at 24 to 26 weeks,” argues Frances Kissling, a longtime proponent of abortion, in the Washington Post.

Kissling is right. Most people, including those who are pro-life, share the common intuition that late abortion is worse than early abortion. This intuition seems to undermine the consistent defense of life because it leaves an opening for proponents of abortion to justify at least early abortions on grounds that pro-lifers share. Thus the challenge we face.

A gradualist view of human moral worth appears to be an attractive mean between two extremes. At one extreme, absolutist critics of abortion hold that abortion is always wrong and that the basic moral status of every human being is equal. At the other, absolutist defenders of abortion hold that it is always ethically permissible, even moments before the birth of a full-term baby. The gradualist view captures the apparently reasonable middle ground and may seem to provide the compromise position that so many seek.

Gradualists like Warnock and Kissling seem to have the rhetorical and political advantage, but no sound argument supports the idea that the moral status of a human being—his or her basic rights—is linked to his or her stage of physiological development. That view would call into question one of the most fundamental principles of democratic society: the basic equality of all human beings. If the painful lessons of history are any guide, we must reject any call to divide the human family into those who have basic rights and those who do not.

We should reject, for example, the analogy between the gradual development of a right to life and the gradual attainment of other rights. There is a radical difference between the right to life and the rights to vote or drive or hold public office. Those rights can be enjoyed only by those who can meet the corresponding responsibilities. Five-year-olds have no right to drive, because they cannot meet the responsibilities of drivers. But the right to life does not have any corresponding responsibilities, and so it may be enjoyed by those who cannot discharge any duties, like children before the age of reason or mentally handicapped adults. Although some rights are attained gradually as the person matures, the right to life is not one of them.

We should also reject the gradualist appeal to moderation. It offers a mean between the extremes of holding that personhood begins at conception and of holding that personhood begins at birth. But, as Aristotle points out in the Nicomachean Ethics, not everything admits of a virtuous mean. The mathematical mean between killing one hundred innocent people and killing no innocent people is killing fifty innocent people—a mean, however, that is not virtuous but vicious. The mean between holding that no women have rights and that all women have rights is that just some women have rights, and that mean, too, is vicious rather than virtuous. The moderation of the gradualist view is no evidence of its truth.

More important is that we can account for the greater wrong of late-term abortion without denying the basic equality of all human beings, including those in the womb. There are, as the philosopher Andrew Peach has argued, important ethical differences between late and early abortion that do not require belief in evolving fetal worth.

First, just as murder by torturous means is worse than murder by painless means, so too late-term abortion involving fetal pain is worse than killing of the unborn that does not cause pain. Second, the more easily an obligation can be met, the worse it is not to meet it. To fail to save a man’s life by refusing to walk two blocks is worse than to fail to save his life by refusing to run ten miles. But to finish carrying a pregnancy already several months along is easier (all things being equal) than to finish carrying a pregnancy that has only just begun, thus later abortion is worse than earlier abortion.

Third, later in pregnancy the humanity of the unborn is more evident. Fourth, an action taken deliberately is worse than one taken in panic. Becoming pregnant unexpectedly may induce shock and panic, which lessens the culpability of those who choose abortion then, but as passions cool the choice becomes more deliberate and therefore worse. Finally, the length of a relationship—in this case, between a mother and her unborn child and, to a lesser extent, between the child and his or her father, siblings, and neighbors—affects the ethics of unilaterally ending it.

A sixth argument (not mentioned by Peach) is that late abortion poses greater risk to the woman’s health than does early abortion. Given a general obligation to care for one’s health, a woman choosing the more dangerous late abortion would be committing a greater wrong than if she chose the safer early abortion.

These six reasons justify the common moral intuition that late abortion is worse than early abortion, without justifying early abortion and without denying human equality. However, the gradualist view that the unborn child increases in moral worth as the pregnancy progresses, and the implicit justification of earlier abortions, might still be vindicated on other grounds.

Some defenders of abortion, for example, are drawn to the gradualist view because of the weakness of other ways of justifying abortion, ways that point to a single characteristic—for example, implantation, the development of a brain, being viable, having conscious desires, the ability to experience pain, the inability to twin, being born—that transforms what was merely a human being with no rights into a human person like us. The presence or absence of these characteristics cannot justify abortion.

Some defenders of abortion, for example, hold that beings who cannot experience physical pain have no moral worth, but it is not just the human being in utero at a certain stage of development who cannot experience pain. Those with chronic insensitivity-to-pain syndrome (CIPS) feel no pain whatsoever. The documentary A Life Without Pain depicts the life of Gabby Gingras, a five-year-old girl with CIPS. When her teeth came in, she began to chew off her fingers. She must wear safety goggles lest she damage her eyes by rubbing them too hard. Despite her disability, she is a happy little girl who enjoys playing with her sister and who loves and is loved by her family. Except for her inability to experience pain, she is like any other kindergartner. No one believes—I hope—that Gabby has no moral worth.

None of the characteristics typically proposed by defenders of abortion justifies the exclusion of a human being from full protection. Some are overinclusive, granting the right to life to beings that obviously do not have it. If sentience bestows basic moral worth, we have to recognize the right to life of every worm, wasp, and weasel. Others are underinclusive. If self-awareness bestows moral worth, not only newborns but also adults with serious mental disability merit no protection. Still others do not secure the equal moral worth of all human persons. If conscious desires bestow moral worth, not everyone equally deserves to live. Finally, still other characteristics do not distinguish persons from non-persons because they are episodically related to the human person. Consciousness cannot bestow moral worth because no one is always conscious.

The gradualist tries to overcome these problems by combining these characteristics, treating them as a continuum. But this won’t work. Indeed, if consistently held, the gradualist position entails that killing a twenty-year-old is worse than killing a fourteen-year-old and that killing a fourteen-year-old is worse than killing a six-year-old. But of course this is nonsense, and not even the gradualist philosophers believe it. Human development and moral status are simply not linked like that.

In addition, some human beings in utero are more physiologically developed than some human beings after birth. Compare a pregnancy that continues two weeks past the due date to a baby born prematurely at twenty-five weeks. The more physiologically developed human being remains within the uterus; the less physiologically developed human being is found outside his or her mother in the nursery. If the gradualist view were true, killing a baby born at twenty-five weeks would be more justifiable than aborting one at forty-two weeks’ gestation. No one thinks this, not even the gradualists.

Adding more characteristics that grant moral status, as gradualists do, does not make the gradualist case any stronger. Invalid or unsound arguments do not become stronger when combined. If neither sentience nor the ability to experience pain grants moral worth, neither do the two of them taken together.

A final argument in favor of the developmental view is that people generally do distinguish between the killing of a human fetus and the killing of an adult. They can do so as well from the pro-life view, but without thereby giving up the principle that every innocent human being has an equal right to life. All intentional killing of innocent human beings violates that right, which all of them enjoy, but killing an embryonic human being and killing an adult human being are not equally wrong in other respects. Killing an innocent adult harms the communities that the person contributed to and makes other adults fear for their own lives. None of these harms is involved in taking unborn human life. Similarly, killing a private citizen and killing a prime minister are equally wrong, because the two have an equal right to live, but killing the prime minister may also harm the economy or social stability and perhaps even prompt retaliation or war.

The common intuition—shared, in general, by advocates and opponents of abortion alike—that late abortion is worse than early abortion seems to undermine the basic equality of all human beings and to help justify early abortion. In fact, it implies no such thing. Circumstantially, no two cases of intentional killing of the innocent are exactly alike. Intrinsically, however, every case is identical, as an act that unjustly deprives the victim of life. That it is worse to kill a human adult than to kill a human being in utero, and worse to kill a child already born than to kill one at the embryonic stage, does not in any way justify the killing of the latter.

Christopher Kaczor is professor of philosophy at Loyola Marymount University and author of The Ethics of Abortion: Women’s Rights, Human Life, and the Question of Justice (Routledge).