Two of the cases that divide people most sharply turn on the same two questions, and once those are isolated the argument becomes tractable even where it stays unresolved.
The questions are whether killing differs morally from allowing to die, which the lesson on duties raised and did not settle, and who has moral status, which the lesson on who counts raised and did not settle either. Euthanasia and abortion are where those two abstractions meet institutions, laws and actual people, and the point of taking them together is to show that the disagreement is structured rather than a clash of raw sentiment.
Killing and letting die
James Rachels put the question at its sharpest in the New England Journal of Medicine in 1975, with a pair of cases designed to isolate one variable.
Smith stands to gain a large inheritance if his six-year-old cousin dies. He drowns the boy in his bath and arranges it to look like an accident. Jones stands to gain the same inheritance in the same way. He enters the bathroom intending to drown the boy, and as he does so the child slips, strikes his head and falls face down in the water. Jones stands ready to push him under if necessary, but it is not necessary. He watches, doing nothing, and the boy drowns.
Rachels asks whether Jones's conduct is less reprehensible than Smith's. Almost nobody says it is. Since the only difference between the two is that one killed and the other let die, the bare difference between killing and letting die cannot itself be morally significant. He draws a practical conclusion for medicine: if it is permissible to withdraw treatment from a patient and let them die slowly, it cannot be the mere fact of killing that forbids giving an injection that ends the same life quickly, and a doctrine that permits the slower death while forbidding the faster one is producing more suffering for no reason.
The argument is good and its limits are real. Two objections have force. The cases equalise everything except the mechanism, including motive, intention and consequence, which is what makes them so vivid; but a distinction can be morally significant in general without making a difference in a case where the agent is a murderer either way, just as whether you shot or poisoned someone makes no difference when you meant to kill them. The second objection is about what the distinction is usually doing. Its point in ordinary morality is not to excuse people who want a death; it is to explain why you are required not to kill any of the millions of strangers you could kill, and not required to save any of the millions you could save. That asymmetry is real, enormously consequential, and Rachels's pair does not touch it.
The fair conclusion is narrower than Rachels wanted and still substantial: the bare difference does not do the work by itself, and where intention, consent and outcome are all the same, an appeal to the distinction alone is not enough to separate two cases.
What the law does with it
Legal systems have, almost without exception, adopted a position the argument above puts under pressure: they permit letting die and forbid killing.
In Airedale NHS Trust v Bland in 1993, the House of Lords permitted the withdrawal of artificial nutrition and hydration from Tony Bland, who had been in a persistent vegetative state since the Hillsborough disaster four years earlier. The reasoning was that continued treatment was not in his best interests and that withdrawing it was an omission rather than an act, so no crime was committed. Several of the judges said in terms that the distinction they were relying on was of doubtful moral coherence, and that Parliament rather than the courts should address it. Nothing has since.
In the United States, Cruzan in 1990 recognised a competent person's constitutionally protected liberty interest in refusing life-sustaining treatment, and Vacco v Quill in 1997 upheld a state ban on assisted suicide against the argument that it was inconsistent with the right to refuse treatment. The Court held the distinction between the two was rational: a patient who refuses treatment dies of the underlying disease, while one who takes lethal medication is killed by it, and intent differs in the two cases.
So the legal architecture rests on doing versus allowing and on intention, exactly the two distinctions that have the most trouble in philosophy, and the judges know it.
Example. A patient with motor neurone disease is on a ventilator and asks for it to be switched off, knowing she will die within minutes. Her doctor does so. Compare this with the doctor administering a lethal injection at her request.
Legally the two are entirely different: the first is required, since continuing to treat a competent patient who refuses is a battery, and the second is murder in most jurisdictions. Morally the differences are hard to sustain under the pressure of the case. The consent is identical, the outcome is identical, the intention of the patient is identical, and the doctor who flips the switch knows exactly what will follow. The main candidate difference is causal: switching off the ventilator lets the disease kill her, while the injection kills her. That is a real difference and it is doing less work than it appears, because it was the doctor's earlier act that placed her on the ventilator, so switching it off is arguably the removal of a barrier the doctor supplied rather than a pure omission. What remains defensible is not that the two acts differ in gravity but that a legal rule permitting only the first is easier to police, which is a reason of a completely different kind and should be argued as such.
Now you. Does Rachels's argument show that active euthanasia should be legal?
Answer
No, and seeing why is a useful exercise in keeping conclusions inside their premises. The argument shows that the bare distinction between killing and letting die cannot bear the weight, which removes one argument against legalisation. Everything else remains open. Legalisation depends further on whether the patient's consent is genuine and informed, on whether a workable set of safeguards exists, on what effects a permission has on vulnerable people and on the practice of medicine, and on whether desperate requests reflect settled wishes or treatable depression. Those are empirical questions, and Rachels's thought experiment says nothing about them. A reader who came away thinking the case settles the policy has made the mistake this course warns against most often: taking a valid argument against one premise as an argument for a whole position.
What the euthanasia data shows
Because several jurisdictions have now permitted assisted dying for decades, some of the argument is empirical, and the figures deserve to be quoted accurately.
The Netherlands legalised euthanasia and physician-assisted suicide in 2002, requiring unbearable suffering with no prospect of improvement, a voluntary and well-considered request, a second physician's opinion, and reporting to a review committee. The regional review committees reported 8,720 cases in 2022, about 5 percent of all deaths in the country. Belgium legalised in the same year. Canada introduced medical assistance in dying in 2016, and Health Canada reported 13,241 provisions in 2022, about 4 percent of all deaths.
Oregon's Death with Dignity Act, passed in 1997 and in force from 1998, is a narrower model: physicians may prescribe but not administer, the patient must be terminally ill with a prognosis of six months or less, and the numbers run in the hundreds per year, well under one percent of deaths in the state.
The slippery slope argument says that a permission granted for one class of case will spread. The honest reading of the record is that this has partly happened, and that whether it counts as a slope depends on a moral judgement rather than on the data. The Dutch and Belgian laws were written in terms of unbearable suffering rather than terminal illness, so their extension to psychiatric conditions and advanced dementia was a consequence of the original criterion rather than a departure from it, and those cases remain a small fraction, in the low hundreds a year in the Netherlands. Canada legislated in 2016 for those whose death was reasonably foreseeable, removed that requirement in 2021 after a court ruling, and has repeatedly postponed extension to cases where mental illness is the sole condition. Oregon's criteria have barely changed in a quarter of a century.
What that pattern suggests is that the slope is a function of how the criterion is drafted rather than an inevitable dynamic. A law written around terminal illness has stayed there; a law written around suffering has followed suffering wherever it goes. That is a conclusion an opponent and a supporter can both use, and it is more useful than either side's slogan.
Example. State the slippery slope argument in premises and say which line the data bears on.
(1) Permitting assisted dying for competent, terminally ill patients who request it is acceptable in itself. (2) Once permitted for that class, it will in practice be extended to classes that are not acceptable, such as people who are not dying, people who cannot consent, or people who feel themselves a burden. (3) The extension cannot be prevented by drafting or enforcement. (4) Therefore it should not be permitted at all. The data bears on (2) and (3) and on nothing else, which is worth knowing, because most public argument attacks or defends (1) and then treats the whole case as settled. What the record shows is that (2) has been true where the statutory criterion was suffering and largely false where it was terminal illness, and that (3) is therefore too strong as stated: extension has tracked drafting, so the argument's force depends entirely on which law is proposed. Note that this is a logical slippery slope claim converted into an empirical one, and that only the empirical version can be tested. Someone who means that the extension follows logically from the principle owes an argument rather than a statistic.
Now you. What would count as evidence that vulnerable people are being pressured into requesting assisted death?
Answer
Something with a comparison group, and this is harder than it sounds. Raw counts of cases among elderly or disabled people prove nothing, since those groups are also the ones most likely to face the conditions the law was written for. The useful measures are comparative: whether uptake in a jurisdiction is higher among people with fewer social supports, less access to palliative care, or lower income, after adjusting for disease burden; whether stated reasons in the mandatory reports shift over time from symptoms towards dependency and being a burden; whether rates among people in institutional care exceed those living independently with the same conditions. Some of this is published: Oregon's annual reports record end-of-life concerns, and loss of autonomy and of the ability to engage in enjoyable activities consistently outrank pain, while "burden on family" is cited by a substantial minority, which supporters and opponents read differently. The important discipline is the one from the lesson on method: decide in advance what pattern would count as pressure, then look, rather than looking first and interpreting afterwards.
Thomson's violinist
Judith Jarvis Thomson's "A Defense of Abortion", published in 1971, is the most quoted paper in applied ethics, and its method is what makes it powerful: it grants the opposing premise.
Suppose, she says, that a fetus is a person with a full right to life from conception. Does the conclusion follow? She argues not, with a case. You wake in a hospital bed connected by tubes to a famous unconscious violinist. The Society of Music Lovers has kidnapped you because you alone have the right blood type; his circulatory system is plugged into yours; unplug him and he dies; stay connected for nine months and he will recover fully. The director apologises but says you may not be unplugged, since the violinist is a person with a right to life.
Almost everyone judges that you would be generous to stay and are not required to. If so, a right to life does not include a right to the use of another person's body to sustain it, and the standard argument from personhood to the impermissibility of abortion is invalid even if its premise is true. Thomson adds a distinction that has outlasted the case: we are required to be minimally decent samaritans, not good samaritans, and the law reflects this by rarely requiring anyone to undergo serious cost to save a stranger. Nobody may be compelled to donate a kidney to save a life, even a child's, which is a striking asymmetry with what is demanded of a pregnant woman.
The objections are focused and serious. The violinist case involves no responsibility for the dependency, whereas most pregnancies follow a voluntary act with a known risk, and many people think you may not create a dependency and then withdraw. Thomson's reply is the people-seeds case, in which seeds drift through windows and may take root despite screens, so that even a person who takes precautions can find themselves responsible in a sense that does not obviously generate a duty. Critics also press the distinction between unplugging, which lets the violinist die of his ailment, and abortion procedures that kill directly, which puts the earlier part of this lesson to work on the other side. The case is therefore decisive against one argument, the simple one from personhood, and not against the position as a whole.
Marquis and the future like ours
Don Marquis published the strongest secular argument on the other side in 1989, and its strategy is also to avoid the disputed ground.
He asks first why killing an adult is wrong, and rejects the usual answers. It is not the effect on others, or killing a hermit would be permissible. It is not the brutalising effect on the killer, which is a derivative wrong. What makes killing you wrong is what it does to you: it deprives you of your future, of all the experiences, activities, projects and enjoyments that would otherwise have made up your life. Call that a future like ours.
Then the argument runs in one step. A standard fetus has a future like ours in exactly the same sense: a set of experiences and projects that it will have if it is not killed. So abortion is wrong for the very same reason killing an adult is wrong, and no claim about personhood, souls or species is needed.
The argument's power is that it explains rather than asserts, which is the standard this course has applied throughout, and that it grounds the wrongness of killing in something that also explains why killing children is wrong and why euthanasia for someone with no valuable future left may not be.
The objections are correspondingly precise. Contraception seems to deprive a possible person of a future too, and Marquis replies that there is no identifiable subject before conception to be deprived, since neither the sperm nor the egg is the individual who would exist. Critics reply that the same problem arises earlier than he wants, since a zygote can twin for about fourteen days, so there is no determinate individual to have a future during that window. Others attack the account of the wrongness of killing, arguing that what matters is the thwarting of a subject's own desires and plans, which a fetus has none of, so that a being with a valuable future but no interest in it is not wronged in the same way.
Example. Which of Thomson's and Marquis's arguments does each of these claims engage? (a) "A fetus is not a person." (b) "You may not create a dependency and then end it." (c) "Killing is wrong because it thwarts a being's own plans."
(a) engages neither, which is the point of both papers: Thomson grants personhood and argues the conclusion still fails, and Marquis never uses personhood, so someone who spends the argument on the status of the fetus is missing both of the strongest positions in the literature. (b) engages Thomson, at exactly the place she is weakest, by attacking the analogy between an unchosen kidnapping and a foreseeable consequence of a voluntary act. (c) engages Marquis, by offering a rival account of why killing is wrong that a fetus does not satisfy, and it is the standard reply; its cost is that it has trouble explaining why killing a person in a dreamless sleep, or a temporarily comatose patient with no current plans, is wrong.
Now you. Which of the two arguments does the case of a pregnancy resulting from rape bear on, and what does that tell you about the structure of the debate?
Answer
It bears on Thomson and not on Marquis, and the asymmetry is informative. Thomson's violinist is a case of a dependency created without the host's consent, which maps onto pregnancy from rape exactly, so her argument is at its strongest there and weakest in the case of a pregnancy following a voluntary act. Marquis's argument is untouched, because the fetus has a future like ours regardless of how it was conceived, and he accepts this consequence explicitly. The structural point is that positions which look like a single package are really several arguments with different scopes, which is why so many people hold apparently inconsistent combinations of views, such as permitting abortion after rape and forbidding it otherwise. That combination is not confused: it is what you get if you accept Thomson and reject Marquis. Knowing that turns a shouting match into a question about which of two premises to defend.
Where the frameworks land
Setting the three normative families against these cases shows that they do not divide the way people expect.
On euthanasia, a consequentialist assesses suffering prevented against risks of error and abuse, and generally supports a regulated permission. A Kantian is genuinely split: autonomy is the foundational value, which supports a right to decide the manner of one's death, and Kant himself argued that suicide treats one's own person as a means to the relief of suffering, so both wings of the tradition are represented in the current literature. A virtue ethicist asks what a compassionate and just doctor does, and how a society that kills its dying differs from one that does not, which reframes the question towards the quality of care rather than towards permissions. A contractualist weighs the complaint of a person left to die badly against that of a vulnerable person who might be pressured.
On abortion, the split runs through moral status rather than through the theories. A consequentialist who counts sentience finds little welfare at stake early in pregnancy and a great deal at stake for the woman. A Kantian who counts rational agency reaches a similar verdict on the fetus and a stronger one about the woman's autonomy, while a Kantian who counts potential rational agency does not. Marquis's argument, notably, is available to any of them. That is why abortion is not a disagreement between consequentialists and deontologists, and why arguments conducted as though it were make no progress.
What can be settled
Three things can. The bare distinction between killing and letting die does not carry the weight the law places on it, which is a philosophical result. The slippery slope in assisted dying is a matter of how the criterion is drafted rather than an inevitability, which is an empirical result. And the standard argument from fetal personhood to the impermissibility of abortion is invalid, which is Thomson's result, whatever one thinks of her conclusion. What cannot be settled from here is the status of the fetus, and no amount of further argument about anything else will substitute for it.
The remaining case in this course is different in kind. It divides people much less loudly, almost nobody defends the position most people take, and the cost of getting it wrong is measured in millions of lives a year.