No right to lie, not even to the murderer

The murderer at the door (Kant against Benjamin Constant)

Immanuel Kant 1724 · 1804Set the limits of reason; act from duty.

What it claims

It is not permitted to lie to the murderer, even to save one's friend. Being truthful in all one's statements is a sacred command of reason.

Why

Telling the truth is a duty without exception, and lying, even to a murderer, wrongs humanity as a whole.

The same idea through history

Benjamin Constant1797In Des réactions politiques, Benjamin Constant cites a "German philosopher" for whom lying to murderers looking for your friend would be a crime. He sees it as proof that a principle taken absolutely would make all society impossible.

Immanuel Kant1797Kant replies a few months later, in a short article: he admits being that philosopher and holds his position, defending it as a duty of right.

Christine Korsgaard1986Christine Korsgaard rereads the debate with the formulas of the categorical imperative: the ban on lying holds in an ideal world, the "kingdom of ends", but faced with evil one may depart from it.

In short

"No right to lie, not even to the murderer" is an argument by Immanuel Kant (On a Supposed Right to Lie from Benevolent Motives, 1797, 1797) on the question "What makes something right?" (answer: duty). Its claim: It is not permitted to lie to the murderer, even to save one's friend. Being truthful in all one's statements is a sacred command of reason. According to AskPhilosophy's logic check (Z3 solver), the conclusion does follow from its 4 premises. AskPhilosophy presents 3 objections, 3 of them with a documented reply, and the original text behind each premise, checked word for word.

On a Supposed Right to Lie from Benevolent Motives, 1797

Valid

A murderer knocks at your door and asks whether your friend, whom he is chasing, is hiding in your house. Do you have the right to lie to save him? Benjamin Constant says yes, and accuses a "German philosopher" of saying no. Kant answers in 1797: even here, lying is not a right. It is one of the best-known debates in ethics.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.

Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P5, one could accept P1 to P4 and still say: this lie does a wrong, but a smaller wrong than an innocent's death, so it is permitted. That is exactly Mill's position.

The argument is valid: P1, P2 and P4 yield an exceptionless duty, P3 says that lying does wrong, and P5 draws the prohibition. The whole debate is about P5 (can consequences lift a duty?), P2 (is the duty of truth owed to a murderer?) and P1 (can one really not stay silent?).

Analogy. A currency is only worth something if people can trust it. A forged note, even given for a good cause, damages everyone's trust in the money. For Kant, every lie is a forged note in the currency of speech.

Objections

Each objection is a conversation: click to see who replies and where the debate stands.

Benjamin Constant 1797 · attacks premise 2

A duty always corresponds to someone else's right: where there is no right, there is no duty. Telling the truth is therefore a duty only towards those who have a right to the truth. But the murderer has no right to a truth that harms others. So we do not owe him the truth, and the principle becomes applicable without being given up.

Kant replies

Kant 1797

"Having a right to the truth" is meaningless: truth is not a property granted to one and refused to another. The duty of truthfulness makes no distinction between persons. And Constant confuses harming with wronging: if the truth harms the hidden friend, it is by accident; whoever tells the truth commits no injustice.

Christine Korsgaard 1986

Kant is wrong about this case, and it can be shown with his own tools. The universalisation test lets this lie pass: it works even if everyone does it, because the murderer believes we do not know who he is. The formula of humanity is stricter: in an ideal "kingdom of ends", neither deception nor coercion is ever permitted. But this ideal is not made for dealing with evil: faced with the murderer, one may depart from it, and the lie becomes a defence against someone who wants to use us.

The debate goes on (our summary) The debate is still lively. Many readers of Kant side with Korsgaard and Constant on this case, without giving up the rest of his ethics. Others recall that Kant speaks here of a duty of right (not ruining trust in statements), not of a calculation. In French schools, this debate is often used to contrast the ethics of duty with the ethics of consequences.

John Stuart Mill 1861 · attacks premise 5

Mill grants that the rule of truthfulness is immensely useful: every lie weakens the trust on which all social well-being depends. But even this sacred rule admits of exceptions, acknowledged by all moralists: for example withholding information from a malefactor, when that is the only way to protect someone from a great undeserved evil. Refusing this exception leads to an absurd consequence: letting an innocent be killed.

Kant replies

Kant 1797 · Kant's anticipated reply (1797)

We do not know the consequences. If you tell the truth, the friend may already have left unseen, or the neighbours may catch the murderer while he searches the house. If you lie and the friend, gone out without your knowledge, meets the murderer, you are responsible for his death. Whoever lies, even with good intentions, answers for all the consequences of the lie.

Christine Korsgaard 1986

Kant's advantage is a well-defined responsibility: if we act as we ought, bad outcomes are not our fault. But in the case of the murderer at the door, it seems grotesque simply to say that we have done our part by telling the truth and that the rest is not our concern.

The debate goes on (our summary) Most commentators find the argument from uncertainty weak: in many cases we know well enough what will happen. Kant's defenders reply that this is not his real point: a duty that can be lifted as soon as the consequences look serious is no longer a duty, and Mill's calculation leaves everyone the judge of the exceptions.

W. D. Ross 1930 · attacks premise 4

Our duties are not absolute, they hold "at first sight" (prima facie): not lying, keeping one's word, but also helping and not harming. When two duties conflict, we must judge which is stronger in the situation. Faced with the murderer, the duty to protect a life outweighs the duty to tell the truth.

Kant replies

Kant 1797 · Kant's anticipated reply (1797)

A real conflict of duties is unthinkable: two opposite rules cannot both be necessary at once. If it is a duty to act on one, acting on the other is contrary to duty. There can be two grounds of obligation that conflict, but then the stronger ground makes the duty, and the other is not one.

The debate goes on (our summary) So Kant grants that "grounds of obligation" are weighed. The question becomes: why would the ground for telling the truth always prevail over the ground for protecting a life? Ross holds that no fixed rule can tell in advance and that we must judge case by case; Kantians fear that we then lose any reliable rule.

What today's voices say

Defend it

Michael SandelLecture 13 tests Kant's view that even white lies violate dignity, with the case of lying to a would-be killer.