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Switching Wine Glasses

Lawrence Crocker asks when it’s right to do the Chateau shuffle.

You may have wondered when it is morally permissible to switch wine glasses if yours could be poisoned. Then again, perhaps this question does not arise so often in your social circle. Fictional characters are not always so lucky.

In E.T.A. Hoffman’s 1815 novel, The Devil’s Elixir, the protagonist Brother Medardus suspects that he’s about to be poisoned by his lover, Baroness Euphemie, in whose household he’s playing the role of spiritual counselor. When Euphemie’s head is turned Medardus switches her wine glass with his. He understands himself to be guilty of murder for her subsequent death from the poison. It was suspect coffee and ice cream in Ossian’s Ride, the 1959 sci fi spy thriller by astrophysicist Fred Hoyle. Thomas Sherwood performs the switch when his false friend is away from the table, and later watches as the latter passes out over the chessboard. Sherwood feels no compunction at all for the switch. In the film The Princess Bride, Vizzini switches wine glasses with The Man In Black – uselessly, as it turned out, as The Man In Black had poisoned both glasses, having prepared for the encounter by developing a tolerance to the poison.

It may seem bootless to pursue the morality and the law of a practice that comes up only in fiction. No legislature has debated the law of glass switching, and neither bench nor bar is clamoring for a clarification. During my misspent middle age, rather than teaching philosophy, among other things I prosecuted and defended criminal cases. I did not prosecute or defend a single poison switch case, and I did not hear of anyone else handling a case with even the remotest resemblance.

Yet philosophy often sharpens concepts by considering hypothetical cases – frequently cases far more hypothetical than these. Here an examination of the morality of repositioning possibly poison potables will reveal elements of the structure of the moral justification of self-defense. It will also shed some light on how the criminal and civil justifications of self-defense ought to be understood. In law journal articles about such matters, it is often hard to tell whether the author is arguing how the law is, or how the law should be. Some versions of natural law theory say that what the law should be ought to determine what the law is. Insofar as what follows bears upon the law of crimes or of torts (civil damages for injury), my concern will be that of applied normative ethics: What should the law be?

Medardus was persuaded that his switching the glasses Euphemie had prepared made him guilty of murder. Was he right as a moral matter? Or conversely, was Hoyle’s Sherwood right in feeling no guilt for his enemy’s emergency hospitalization? More generally – when is it morally permitted, and when morally forbidden, to switch glasses on suspicion of poison?

There is a certain elegance in switching glasses if you are suspicious that you are being poisoned, but uncertain. If your suspicion of poison turns out to be wrong, switching does no harm. Glass switching is in this respect very different from traditional forms of self-defense such as shooting and stabbing. The case in moral defense of Medardus is unquestionably better than if he had stabbed Euphemie or put poison in her glass himself. But is it good enough?

Very Low Likelihood of Poison

It is often helpful in cases on a moral borderline to work in towards the case from each extreme.

At one extreme, consider Oscar, who is slightly paranoid. He always switches his glass with that of his host. Though he attempts stealth, he has been caught at it so many times that it has become an anticipated affectation. If taken aside and asked seriously, Oscar would volunteer some reason for thinking he might be about to be poisoned. The reason, however, would never pass muster with the rest of us. Whenever he’s caught in a switch, Oscar makes a joke of it, saying, “One can never be too careful.”

Suppose a new acquaintance of Oscar’s really does try to poison him, and subsequently succumbs to her own machinations after Oscar’s surreptitious switch. If Oscar’s switching of glasses was as groundless as usual, he’s guilty of nothing. No reasonable person in Oscar’s position would have thought the switch posed any danger. The intending poisoner was hoist on her own petard. She could hardly complain with her dying breath that she was unfairly victimized by Oscar’s switch.

It is tempting to generalize, reasoning that the elegance of glass switching reduces to this permissive argument:

If you are contemplating switching glasses, there are two possible outcomes: either nothing will happen, because there was no poison, or you will have saved yourself at the expense of an intending evildoer. Therefore, it is always permissible surreptitiously to switch glasses with someone in a position to put poison into the glass placed in front of you.

It would seem to follow that both morally and legally you should always be able to switch. In fact, it might appear that the better the reason you have to suspect poison, the better motivated your switch is morally.

Certainty of Poison

However, the permissive argument runs into problems when we look at a case on the opposite extreme from Oscar’s. If you know with certainty that there’s deadly poison in your glass, switching glasses is like pulling the trigger of a loaded pistol. To switch is to use deadly force, and you’re subject to the usual moral and legal rules governing the use of deadly force. In particular, to be justified, the switch must be necessary to protect you from the imminent risk of death or serious injury ( ‘the necessity test’). With certainty of poison, most of the moral elegance of glass switching disappears. You may switch the glasses if you are kidnapped, because under usual legal presumptions, kidnapping involves a continuing risk of death. In a typical social setting, however, you can simply empty your glass into the aspidistra and make a swift exit. Whenever this or similar alternatives are available, you will be criminally liable if you switch a glass that you know to be poisoned – and you should be.

This suggests the following prohibitive argument:

If you are considering a glass switch as a defense against poisoning, the only important case to consider is that in which there turns out to be poison. If there is no poison in the first place, glass switching is inconsequential. We must assume the poison case then, in making the decision. Hence, you can only do the switch if you can pass the necessity test.

Mid-level Probabilities of Poison

Glass switching without any reasonable suspicion of poison (or at random) raises no moral or legal liability for a subsequent death by poisoning. However, glass switching with knowledge of poison leads to liability unless it passes the necessity test. The extremes seem fairly clear. We must however be cautious about generalizing from the argument at either extreme, as each extreme is a good counterexample to its counterpart. For example, by only slight extension, the prohibitive argument would make a thespian morally and legally liable if she fired what she had every reason to believe was a prop pistol at her leading man, and it turned out that someone had substituted a loaded gun. Like us, she would know that such substitutions are possible, if extraordinarily unlikely.

So let’s now work in a little bit from the extreme cases. Suppose that Penny is in a crucial interview for an important job. She discovers that the junior of her two interviewers, whom she will be replacing, is Quinton, someone she knew from college. After Penny accepts the offer of refreshment, Quinton prepares three lemonades and places one of them directly in front of her. Quinton and the senior interviewer are then called out of the room for a conference call.

I want us to consider two variants. In Penny1, Penny sees Quinton put something in her lemonade. She knows that Quinton was always fond of malicious pranks. She is confident that he has given her something that will cause her discomfort or embarrassment, but nothing really injurious.

In Penny2 there was a white hot enmity between Penny and Quinton in their school days, and Penny believes Quinton to be capable of doing her serious injury. In this variant, however, Penny is not at all certain that Quinton put something in her drink. She caught a glimpse out of the corner of her eye of an odd motion as he was pouring her lemonade, but it might have been nothing. Still, she is made somewhat anxious by the possibility that Quinton has put poison in her glass.

In Penny1, because of the certainty that there is something in the lemonade, the necessity requirement from the prohibitive argument is triggered. Penny should not put the adulterated lemonade in front of Quinton unless there is no better option. However, what would make a better option is eased by the fact that the adulterant is unlikely to be seriously injurious. Moreover, in determining morally better alternatives to the glass switch, the costs to Quinton and to Penny are not of equal weight. Both morality and law have a preference for victims over aggressors. You are permitted deadly force not only to prevent being killed, but also to prevent being raped or seriously injured, for example. Attackers are not to be gratuitously ill-used, but their well-being does not weigh equally with that of defenders. In Penny1, Quinton is unambiguously an aggressor.

Here Penny has alternatives such as confronting Quinton, walking out on the interview, knocking over her glass in feigned awkwardness, or saying that she no longer wants the lemonade she had enthused about just moments earlier. None of these alternatives would be particularly appealing, as each carries a real likelihood of turning a good interview bad. If she switches glasses instead, Quinton will get the burping fit, nausea, diarrhoea or flatulence attack he had planned for her, which would serve him right. In light of his having created the problem in the first place, it is better he be saddled with its consequences, even if they are somewhat worse for him than the costs to Penny of the next best alternative. In fact, if Penny is confident that whatever is in her glass is not dangerous, then she may switch the glasses, unless she has a truly costless alternative.

Admittedly, even a mild poisoning probably counts as a criminal assault, and certainly as an intentional tort. The ‘black letter’ law would require Penny to absorb a cost (other than a physical injury) to save Quinton from a stomach ache. However, n o jury is going to convict Penny or award Quinton damages for her causing him the unpleasant symptoms he intended for her. This reflects the moral reality. If we want our criminal codes to be morally correct on this detail, the ‘necessity’ requirement should be amended or interpreted so that a victim may reflect a modest evil back onto an aggressor if the victim would otherwise have to absorb some significant cost herself.

In Penny2, Penny does not know that Quinton put something in her drink, but believes that if he did, it could be a serious poison. If she knew that he had, she could not switch. The danger to Quinton would be too great for that. Morally and legally she would have to sacrifice her interview. However, in Penny2, the probability of poison is very low. So if her lemonade is drunk by either Quinton or Penny, there is low probability of harm. The probabilistically-adjusted expected harm is so low that it is less than the harm to Penny of her alternatives. So the lemonade should be drunk rather than spilt. The question is, who should drink it? It seems clear that it should be Quinton, if possible. In the unlikely event that there is a burden to be born, again, it is Quinton who created it, and he should bear it.

So glass switching seems morally permissible if there is a high probability of mild poison, or a slight probability of serious poison, as well as in Oscar’s case, where there was negligible probability of any poison. Again, only in the case of certainty of a serious poison must the intended victim absorb some significant cost instead of switching glasses. It would be necessary to look at additional intermediate cases to be sure, but from what we’ve considered it appears that the cost you must absorb as an alternative to surreptitiously switching your possibly poisoned wine drops quickly as the probability of poison or the probable injuriousness of the poison falls.

Why should the morality of self-defense be so generous to glass switchers? Generally, morality and law would demand too much if they did not permit actions like these by those who are threatened with injury. So let’s take a brief look at wider questions of self-defense theory.

Moral Psychology and Self-Defense Theory

It is sometimes piously asserted that self-defense is a justification precisely because it leads either to the socially most desirable result, or to the just result. Though popular among theorists, neither of these propositions can be correct. They founder on the fact that it is morally permissible to use deadly force (with a pistol, perhaps) to protect oneself against a bevy of homicidal maniacs who are in that condition quite temporarily for reasons utterly beyond their control. Suppose they are coming at you with axes, having unwittingly imbibed hallucinogenic punch... What can you morally do?

The privilege of ‘self-defense’ keeps morality and the law from being too demanding for mere mortals. To oblige you to leave your revolver holstered in the face of berserk on-rushing axe-wielding assailants is to ask too much; and to obligate you to risk an interview to protect a prankster from a self-inflicted stomach ache is also to ask too much. Both morality and law are systems for guiding conduct, and if they are to be effective in guiding conduct they must correlate at least roughly with our moral psychology. You are morally required to sacrifice yourself when attacked only if that self-sacrifice is reasonably available psychologically. As Hume argued, ‘ought’ implies ‘can’.

Self-Help Retributivism

Could we go one step further, to the conclusion that if I know that the poison is mild I can switch even if I have a completely costless alternative? Perhaps if the wine were served among shipwreck victims on a desert island the switch would be permissible as a dispensation of natural justice. Outside of the state of nature, however, retribution is better left to the courts.

This may seem in tension with my conclusion that Penny could switch weak poison to avoid even a modest inconvenience. However, when we move from low cost alternatives to costless alternatives, we leave self-defense completely behind and cross the border into do-it-yourself retribution. When such self-help constitutes a crime or tort, it is difficult to justify in any state which has a reasonably just courts system.


You may always switch glasses simply on a lark (as long as no poison is suspected). It is ‘black letter law’ and morally sound that you may also switch if you are a kidnap victim or otherwise must switch to save yourself from a serious assault, although you know with certainty your glass is poisoned. More interestingly, you can switch your glass with that of a suspected poisoner if your level of suspicion of poison is low, or if you believe that any poison would not be very dangerous. It is only when the probability of serious poison is fairly high that you are faced with difficult decisions. The more injurious you believe the poison to be, the higher the cost you must absorb in taking alternatives other than switching. The reason that glass switching is so often permissible is a matter of the general preference for self defenders that comes from the necessity that our moral and legal systems should not be psychologically over-demanding.

Where does this leave our friend Medardus, with his mid-level suspicion of a deadly poison? If I were prosecuting Medardus, I would emphasize that he could simply have fled – which he did do very shortly after anyway (and successfully). As defense counsel, however, I would argue that because the mistress of the castle hated him enough to resort to deadly poison, Medardus was in a desperate position – one worse even than that of the average kidnap victim. Had he fled, Euphemie could instantly have raised the hue and cry, sealing his doom. If he thought Euphemie’s minions would slay him on the spot were he to decline the wine and try to exit, Medardus was exercising morally permissible self-defense in switching the wine glasses. You should feel free to do so as well, if you find yourself in the same spot as Medardus, Thomas Sherwood, Penny1, or Penny2.

© Dr Lawrence Crocker 2008

Lawrence Crocker has been both a prosecutor and a criminal defense lawyer. He has taught law at New York University and now teaches philosophy at Dartmouth College, in New Hampshire.

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