Few questions divide democracies as deeply as those about the start of human life. This level sets out the strongest arguments on each side as their best defenders make them. The aim is not to settle the questions but to understand why serious, decent people disagree.
The case that abortion is wrong
The central argument runs: it is wrong to kill an innocent human being; a human embryo or fetus is a living human organism from conception; therefore abortion is wrong. Defenders stress that development from zygote to adult is continuous, so any later line, such as birth or viability, looks arbitrary. The philosopher Don Marquis offered a version in 1989 that does not rely on religion or on calling the fetus a person. He asked what makes killing an adult wrong, and answered that killing deprives the victim of a valuable future of experiences, projects and relationships. A fetus normally has such a future, so killing it is seriously wrong for the same reason.
Critics reply that the argument proves too much or too little. If losing a future is what matters, some ask whether contraception is also wrong; Marquis answered that before conception there is no individual who loses anything. Others say a being with no mental life yet cannot be harmed in the way an adult can.
The case for a right to choose
One line of defense denies that an early fetus has the moral status of a person. In 1973 Mary Anne Warren listed traits such as consciousness, reasoning and self-awareness as marks of personhood, and argued that a fetus has none of them. Critics note that newborns also lack most of these traits, so the view seems to permit too much.
A second, influential line grants the opponent's premise. In 1971 Judith Jarvis Thomson asked readers to imagine waking up connected to a famous violinist whose life depends on using their kidneys for nine months. Most people think you may unplug yourself, even though he will die. Her point was that even if the fetus is a person, a right to life does not include a right to use another person's body. Critics reply that the violinist case is like rape, where the person never agreed to anything, and that in most pregnancies people bear some responsibility for creating a dependent being.
Many people hold a gradualist view between the two: moral status grows as pregnancy goes on, so early abortion is easier to justify than late abortion. Many European laws, which allow abortion on request early in pregnancy and restrict it later, reflect this view.
Law in brief
In the United States, Roe v. Wade (1973) recognized a constitutional right to abortion before viability. Dobbs v. Jackson Women's Health Organization (2022) overruled Roe and returned abortion law to the states, which now range from near total bans to broad access. Other countries have moved in both directions: Ireland voted in 2018 to remove a constitutional ban, while Poland's top court tightened restrictions in 2020.
IVF and the embryo
On 25 July 1978 in Oldham, England, Louise Brown became the first person born through in vitro fertilization, the work of Robert Edwards and Patrick Steptoe. Edwards later won a Nobel Prize. Millions of people have since been born through IVF, which typically creates more embryos than are used. Leftover embryos raise hard questions. Should they be frozen forever, donated, destroyed or used for research?
Britain's Warnock Committee proposed an answer in 1984 that many countries copied: research on embryos would be allowed only up to fourteen days after fertilization. It chose that point because around fourteen days the primitive streak appears and the embryo can no longer split into twins, so it is the earliest point at which a single individual can be identified. Critics on one side say any embryo deserves protection; on the other, some scientists want the limit extended now that embryos can be grown longer in the lab.
Law can treat embryos very differently. In February 2024 Alabama's Supreme Court ruled that frozen embryos count as children under the state's wrongful death law. Several clinics paused IVF until the legislature passed a law shielding them from liability. The case showed how beliefs about the start of life reach far beyond abortion.
Worked example: choosing among embryos
A couple who both carry the gene for cystic fibrosis use IVF and genetic testing of embryos, a technique called preimplantation genetic testing. Of six embryos, two will have the disease. They ask to transfer only an unaffected embryo and to donate the rest to research.
Someone who holds that an embryo has full moral status from conception would object to creating spare embryos, to discarding those with the disease and to research on them. A gradualist would likely see an early embryo as deserving respect but not the protection owed to a born child, and would accept the plan. A disability rights advocate might ask what message is sent when embryos are discarded because of a condition people live with. The couple's own view, that they want to spare a child serious illness, deserves weight too. Mapping the positions this way does not settle the case, but it shows exactly where the disagreement lies.