About the Groundwork

Section I

The Good Will
The End of Practical Reason
Duty and Moral Worth
The Three Propositions
The Feeling of Respect
Conformity to Universal Law
Maxims of Action
The Lying Promise
The Inquiring Murderer

Section II

Hypothetical Imperatives
The Categorical Imperative
The Suicide Example
Perfect and Imperfect Duties
The Contradictions
Moral Realism
The Formula of Humanity
Deontology and Ethical Ends
The Formula of Autonomy
Autonomy and Heteronomy
The Kingdom of Ends

Section III

Freedom of the Will
Free in a Practical Respect
The Hidden Circle
Two Standpoints
The Deduction
Failure of the Deduction


The Inquiring Murderer “To be truthful (honest) in all declarations
is . . . a sacred command of reason prescribing unconditionally, one not to be restricted by any conveniences.”

Taking Kant’s principle of duty to what seems to be a logical conclusion, it should always be wrong to lie. No maxim for lying seems capable of passing the universalization test, since upon the maxim’s universalization the person to whom one would lie can always be expected know she is being lied to. This implication seems to be confirmed by Kant himself, in the quotation above (Kant 1996, 613/8:427). But does his principle of duty really lead to the conclusion that no lie is ever morally permissible—regardless of the consequences?

Lying to the murderer at the door. The classic objection to Kant’s ethical theory as a whole is the case of the inquiring murderer. Knowing that someone is intent on killing your friend, you hide her upstairs; but then he knocks on your door and asks if she is in your house. Your maxim of lying, telling the murderer that your friend has left, seems contrary to the principle of duty; but your telling him the truth seems to make you complicit in your friend’s murder; if you say nothing at all, or if you say “I’d rather not answer that question,” these will be equivalent to telling the truth. That’s the trouble with an ethics like Kant’s that emphasizes exceptionless moral rules, it is said.

Doctoring the maxim. Kant himself bit the bullet on the case of the inquiring murderer: he said that even in that case it would be wrong to lie (Kant 1996). But not all of his followers have agreed that his ethics implies such an unyielding stance. Suppose your maxim is: “I’ll lie to murderers inquiring after the whereabouts of their intended victims, in order to save their lives.” When this is universalized, a murderer might still inquire about his victim if he believes you do not know his intentions. So then your lie will convince him that your friend is not in the house. Even though he would know that everyone lies to murderers inquiring about their victims, he would not think you know he is intent on murdering your friend—so he would take what you say to be the truth (see Korsgaard 1996, 136-7). But that trick won’t work if the murderer announces his intentions up front; because in that case he’ll know that you know what he is up to, and so he will expect you to act on your maxim of lying to murderers. Remember, you cannot save your friend’s life unless the murderer believes you’re telling the truth when you attempt to deceive him. He says, “I’m going to kill that Julia; is she in the house?” and he knows, because of your maxim’s universalization, that everyone lies when they are asked questions like that. So when you lie and answer, “She’s not here,” he knows where she is—poor Julia.

Trap questions. For the problem posed by the case of the inquiring murderer it is essential that the murderer ask a special kind of question. I call these “trap questions” (McCarty 2012). They are traps because, unlike most other questions, they cannot be evaded without conveying a truthful answer. If you answer the inquiring murderer with something truthful but evasive like, “I don’t want to answer that question,” then he knows that his victim is hiding in your house. What makes trap questions interesting here is that asking them seems to be wrong in Kantian ethics. The murderer’s maxim could be, “I’ll ask trap questions in order to learn others’ secrets.” What will happen when that maxim is universalized, and everyone asks such questions for that reason? The responses to those questions will always be evasive. When the murderer asks you if Julia is in the house, your response that you don’t want to answer that question will not inform him whether Julia is in the house or not—because upon the maxim’s universalization, evasive answers will be the standard type of reply to questions like his. Everyone will answer them evasively, in order to render them ineffective for prying out information. So what that means, in Kantian ethics, is that asking trap questions should be morally wrong. You cannot achieve your goal of learning information others want to conceal when your maxim of asking trap questions is universalized and everyone always responds to such questions evasively.

The right to lie. Kant did not think it makes sense for there to be a right to lie. But this has more to do with how he understood rights than with whether it can ever be morally permissible to lie. He considered a right to include an “authorization to coerce” (Kant 1991, 57-8/6:31-2). My having a right to something, like a piece of property, includes my authorization to coerce anyone who would hinder my freedom to use it. Whenever I coerce someone I interfere with their freedom. But if they are interfering with my freedom, then, Kant supposed, I am permitted to interfere with theirs, up to the point that equality of freedom is restored. If they are trespassing on my land, I have a right tell them to get off, even to force them off: although it is not otherwise permissible for me to tell people what to do, and make them do it. It is easy to see that someone who asks a trap question is interfering with my freedom. She is doing something wrong, as established above. But she is also trying to get information from me that I am free to keep to myself. So by Kant’s principles, I have a right to coerce her, in order to cancel the liberty she is taking to constrict my liberty. Yet if I attempted to do something coercive when she asks me a trap question, or when I anticipate that she will, that would be like trying to evade the murderer’s inquiry. My response would convey the truth I do not want to convey, and that I am free not to convey. My view here is that lying is (usually) a permissible response to a trap question asked of me. Because evading such questions will convey the truths I do not want to convey, an effective way to preserve my freedom not to convey it is to lie to trap questioners interfering with my freedom. My lying responses will interfere with their freedom, of course, but this is permitted by Kant’s conception of a right. I am authorized to interfere with the freedom of someone attempting to interfere with mine, in order to restore equality of freedom. So what this means, in ordinary terms, is that by Kant’s own theory of rights we have a right to lie to inquiring murderers. Technically, I think that for Kant’s theory of rights we have a right to say whatever we wish in response to trap questions, whether truthful or otherwise. So saying we have a “right to lie” is probably not the best way to put it.

Benevolent lies. It is pretty well understood that Kantian ethics prohibits lying to someone for his or her own good. But few people would say, and Kantian ethics does not say, that we ought always to seek out people to tell them the truth for their own good. If I know something you don’t know about your personal life, I am ordinarily not obligated to tell you what I know, even if it would be for your own good. But if you ask me about it, that might make a difference. Some think that your asking me to tell you a hard truth about yourself obligates me to tell it, even if I would rather not, because of how it might affect you. The idea is that your having asked, knowing what you are asking for, cancels my obligation to protect you from harm or distress by keeping information from you, so I ought to answer truthfully, and not lie (see Hill 1991). I don’t think this is necessarily so, however. I think it depends on what you ask—if you ask me a trap question in order to find out the information I have about your life, then, because of how I argued above, I think I have the right to lie to you. So I think we are not necessarily obligated to tell others the truth about themselves, or their lives, just because they ask.

The detective and the widow. Consider this case: In a homicide investigation a detective discovers that a shooting victim had been having an extra-marital love affair. After interviewing the “other woman,” the detective concludes that the affair was immaterial to the case. The case is later solved, when evidence comes to light that it was an accidental shooting. But a few days later the bereaved widow meets with the detective and asks, point blank, whether he knows if her late husband had been unfaithful. I think that in this case he as a right to lie. The detective would not otherwise be obligated to contact the widow and tell her what he had discovered about her husband’s fidelity. But her asking about it does not, I think, obligate him to tell her. The detective cannot evade her trap question without conveying a truthful answer, which he may not want to give, which he may not be prepared to give, considering how it may affect her. So he has a right to prevent her from learning the truth, at least from him, by giving a lying response to her question: “Nothing like that turned up,” he can say. There are probably other, morally permissible ways she can discover the truth if she wants to. A trap question is manipulative, and interferes with the freedom of the person asked.

Some noteworthy exceptions. To the general rule that lying responses to trap questions are permissible, some apparent exceptions should be observed. I have no right to lie to you if you ask me whether or not I stole your necklace. If I did steal it, then you are within your rights to get me to confess by means of a manipulative question. You are not interfering with my freedom, since I cannot be free to conceal my crime. You are in fact exercising your authorization to coerce, in order to restore equal freedom. Something similar will be true for a public official, like a police detective. Since her job involves restoring equality of freedom (justice), she is permitted to ask trap questions likely to have that effect. Similarly also, it is not wrong for judges and attorneys to ask trap questions in court. If the questions there go beyond propriety, then they can be dismissed or evaded by legal objection, or by “taking the fifth,” and refusing to answer in order to avoid self-incrimination. Finally, it should be observed explicitly that not just any lie in response to a trap question is permissible. Lies are permissible responses to trap questions because lying, like coercion, can restore a balance of freedom. To “overreach” with a lying response, to lie more than is necessary to preserve one’s freedom, will inevitably and unduly restrict someone else’s freedom, which, of course, is wrong.



Hill, Thomas E., Jr. (1991), “Autonomy and Benevolent Lies,” in Autonomy and Self-Respect (Ithaca, NY: Cornell University Press), 25-42.

Kant, Immanuel (1991), The Metaphysics of Morals, trans. Mary Gregor (Cambridge: Cambridge University Press).

_____ (1996), “On a Supposed Right to Lie from Philanthropy,” in Practical Philosophy, trans. and ed. Mary J. Gregor (Cambridge: Cambridge University Press), 605-15.

Korsgaard, Christine M. (1996), “The Right to Lie: Kant on Dealing with Evil,” in Creating the Kingdom of Ends (Cambridge: Cambridge University Press), 133-58.

McCarty, Richard (2012), “The Right to Lie: Kantian Ethics and the Inquiring Murderer,” American Philosophical Quarterly 49: 331-43.


© Richard McCarty
Department of Philosophy & Religious Studies
East Carolina University

Last modified: April 24, 2015

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