The doctrine (or principle) of double effect is often invoked toexplain the permissibility of an action that causes a serious harm,such as the death of a human being, as a side effect of promoting somegood end. According to the principle of double effect, sometimes it ispermissible to cause a harm as an unintended and merely foreseen sideeffect (or “double effect”) of bringing about a goodresult even though it would not be permissible to cause such a harm asa means to bringing about the same good end.

• 1. Formulations of the principle of double effect
• 2. Applications
• 3. Misinterpretations
• 4. Criticisms
  • 4.1 Consequentialist Objections
  • 4.2 The Problem of Closeness
  • 4.3 The Side Effect Effect
  • 4.4 Direct and Indirect Agency
  • 4.5 Does double effect provide an adequate explanation of the trolley cases?
  • 4.6 Does Double Effect Explain the Permissibility of Risky Rescues and Rescue by Reducing the Extent of Harm?
  • 4.7 The Role of Conventions and Norms in Warfare
• 5. End of Life Decision-Making
  • 5.1 Pain Relief in Palliative Care
  • 5.2 Terminal Sedation
• 6. One principle or many loosely related exceptions to a general prohibition on causing grave harms?
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Formulations of the principle of double effect

Thomas Aquinas is credited with introducing the principle of doubleeffect in his discussion of the permissibility of self-defense in theSumma Theologica (II-II, Qu. 64, Art.7). Killing one’sassailant is justified, he argues, provided one does not intend tokill him. In contrast, Augustine had earlier maintained that killingin self-defense was not permissible, arguing that “privateself-defense can only proceed from some degree of inordinateself-love.” Aquinas observes that “Nothing hinders one actfrom having two effects, only one of which is intended, while theother is beside the intention. … Accordingly, the act ofself-defense may have two effects: one, the saving of one’slife; the other, the slaying of the aggressor.” AsAquinas’s discussion continues, a justification is provided thatrests on characterizing the defensive action as a means to a goal thatis justified: “Therefore, this act, since one’s intentionis to save one’s own life, is not unlawful, seeing that it isnatural to everything to keep itself in being as far aspossible.” However, Aquinas observes, the permissibility ofself-defense is not unconditional: “And yet, though proceedingfrom a good intention, an act may be rendered unlawful if it be out ofproportion to the end. Wherefore, if a man in self-defense uses morethan necessary violence, it will be unlawful, whereas, if he repelforce with moderation, his defense will be lawful.”

The passage can be interpreted as formulating a prohibition onapportioning one’s efforts with killing as the goal guidingone’s actions, which would lead one to act with greaterviciousness than pursuing the goal of self-defense would require.

Later versions of the double effect principle all emphasize thedistinction between causing a morally grave harm as a side effect ofpursuing a good end and causing a morally grave harm as a means ofpursuing a good end. We can summarize this by noting that for certaincategories of morally grave actions, for example, causing the death ofa human being, the principle of double effect combines the claim thatit can be morally permissible to cause a death incidentally as a sideeffect of pursuing a good end with a general prohibition on causingthe death of an innocent human being for the sake of a good end. Theprohibition is absolute in traditional Catholic applications of theprinciple. Two traditional formulations appear below.

The New Catholic Encyclopedia provides four conditions forthe application of the principle of double effect:

1. The act itself must be morally good or at least indifferent.
2. The agent may not positively will the bad effect but may permitit. If he could attain the good effect without the bad effect heshould do so. The bad effect is sometimes said to be indirectlyvoluntary.
3. The good effect must flow from the action at least as immediately(in the order of causality, though not necessarily in the order oftime) as the bad effect. In other words the good effect must beproduced directly by the action, not by the bad effect. Otherwise theagent would be using a bad means to a good end, which is neverallowed.
4. The good effect must be sufficiently desirable to compensate forthe allowing of the bad effect (see Connell, 1021).

The conditions provided by Joseph Mangan include the explicitrequirement that the bad effect not be intended:

A person may licitly perform an action that he foresees will produce agood effect and a bad effect provided that four conditions areverified at one and the same time:

1. that the action in itself from its very object be good or at leastindifferent;
2. that the good effect and not the evil effect be intended;
3. that the good effect be not produced by means of the evileffect;
4. that there be a proportionately grave reason for permitting theevil effect (Mangan 1949, p. 43).

In both of these accounts, the fourth condition, the proportionalitycondition is usually understood to involve determining if the extentof the harm is adequately offset by the magnitude of the proposedbenefit.

Peter Cataldo formulates the first condition in a way that focuses onthe “moral object” of the act:

1′.

The moral object of the act must be good or at least not beintrinsically immoral (Cataldo 2022, 3).

Cataldo also reports that the Catholic moral tradition provides usefulclarification of the fourth “proportionality” condition byrecognizing five different dimensions of assessment: “the degreeof badness of the effect; the degree of dependence of the bad effecton the act; the proximity of the effect to the bad act; the degree ofcertainty that the bad effect will occur; and the degree of obligationto prevent the bad act” (Cataldo 2022, 9. fn. 12).

It is reasonable to assume that agents who regret causing harm will bedisposed to avoid causing the harm or to minimize how much of it theycause. This assumption could be made explicit as an additionalcondition on permissibly causing unintended harm:

5. that agents attempt to minimize the foreseen harm and considerless harmful alternatives.

Michael Walzer (1977) has convincingly argued that agents who causeharm as a foreseen side effect of promoting a good end must be willingto accept additional risk or to forego some benefit in order tominimize how much harm they cause. Whether harm has been minimizedwill depend on the agent’s current circumstances and the optionsavailable.

Double effect might also be part of a secular and non-absolutist viewaccording to which a justification adequate for causing a certain harmas a side effect of pursuing a good end might not be adequate forcausing that harm as a means to the same good end under the samecircumstances.

2. Applications

Many morally reflective people have been persuaded that somethingalong the lines of double effect must be correct. No doubt this isbecause at least some of the examples cited as illustrations of DEhave considerable intuitive appeal.

Terror bomber vs Tactical bomber: The terrorbomber aims to bring about civilian deaths in order to weaken theresolve of the enemy: when his bombs kill civilians this is aconsequence that he intends. The tactical bomber aims at militarytargets while foreseeing that bombing such targets will cause civiliandeaths. When his bombs kill civilians this is a foreseen butunintended consequence of his actions. Even if it is equally certainthat the two bombers will cause the same number of civilian deaths,terror bombing is impermissible while tactical bombing ispermissible.

Euthanasia vs Pain relief that hastens death:A doctor who intends to hasten the death of a terminally illpatient by injecting a large dose of morphine would act impermissiblybecause he intends to bring about the patient’s death. However,a doctor who intended to relieve the patient’s pain with thatsame dose and merely foresaw the hastening of the patient’sdeath would act permissibly. (The mistaken assumption that the use ofopioid drugs for pain relief tends to hasten death is discussed belowin section 5.1.)

Abortion vs Hysterectomy:A doctor whobelieved that abortion was wrong, even in order to save themother’s life, might nevertheless consistently believe that itwould be permissible to perform a hysterectomy on a pregnant womanwith cancer. In carrying out the hysterectomy, the doctor would aim tosave the woman’s life while merely foreseeing the death of thefetus. Performing an abortion, by contrast, would involve intending tokill the fetus as a means to saving the mother.

Pre-emptive Killing vs Active Self-defense:To kill a person whom you know to be plotting to kill youwould be impermissible because it would be a case of intentionalkilling; however, to strike in self-defense against an aggressor ispermissible, even if one foresees that the blow by which one defendsoneself will be fatal.

Suicide vs Heroic Shielding:Sacrificingone’s own life in order to save the lives of others can bedistinguished from suicide by characterizing the agent’sintention: a soldier who throws himself on a live grenade intends toshield others from its blast and merely foresees his own death; bycontrast, a person who commits suicide intends to bring his or her ownlife to an end.

The Trolley Problems, Pushing a Bystander onto a Track tostop the trolley vs Diverting a Trolley onto a track with one personaway from a track with five: You are a bystanderstanding near a switch watching a runaway trolley barrel down a trackon which five people who cannot escape are positioned. Pushing anotherbystander onto the track to stop the trolley would be wrong, manybelieve. However, many believe that it would be permissible to turn aswitch and divert the trolley onto a different track on which oneperson who cannot escape is positioned (examples from Thomson, 1985,based on examples in Foot 1967).

3. Misinterpretations

Does the principle of double effect play the important explanatoryrole that has been claimed for it? To consider this question, one mustbe careful to clarify just what the principle is supposed to explain.Three misinterpretations of the principle’s force or range ofapplication are common.

First, the Doctrine of Double Effect does not claim that the fact thata harm was foreseen and not intended by an agent is sufficient toexplain the permissibility of causing it. Applications of doubleeffect always presuppose that some kind of proportionality conditionhas been satisfied and plausible accounts of double effect requireagents to minimize harms brought about as side effects. Classifyingcivilian casualties during wartime as merely foreseen but unintendedside effects of pursuing a military objective does not show that theagents were not morally responsible for these consequences or thatthey were permissibly brought about. Quite obviously, aphysician’s justification for administering drugs to relieve apatient’s pain while foreseeing the hastening of death as a sideeffect does not depend only on the fact that the physician foreseesbut does not intend the hastening of death; that explanation could notjustify treating the pain of kidney stones with a lethal dose ofmorphine.

A second misinterpretation is fostered by applications of doubleeffect that contrast the foreseen harms that one permissiblyallows to occur with intended harms that one impermissiblycauses by acting to promote a good end. The distinctionbetween causing and allowing can be distinguished from the distinctionbetween intended and merely foreseen consequences of acting (seeDoing vs. Allowing Harm).

A third misinterpretation of double effect bases the impermissibilityof causing harm as a means to a good end on the fact that it iswrongful in itself to intend to cause harm. There are manycircumstances in which agents may cause harms as a means to a good endand in such cases, producing a harm as a means to a good end iscompatible with having an appropriate attitude toward the harm.Surgeons may amputate limbs to save lives while regretting the damage,the disfigurement, and the disability that their actions will cause. Adentist may apologetically probe while instructing her patient“tell me where it hurts”. This is why plausible accountsof double effect insist on the importance of the proportionalitycondition and the requirement to minimize harm and to seek lessharmful alternatives: it is directed at agents who aim at good endsand seek guidance about what they may do to promote them.

4. Criticisms

4.1 Consequentialist Objections

Those who defend the principle of double effect often assume thattheir opponents deny that an agent’s intentions, motives, andattitudes are important factors in determining the permissibility of acourse of action. If the permissibility of an action depended only onthe consequences of the action, or only on the foreseen or foreseeableconsequences of the action, then the distinction that grounds theprinciple of double effect would not have the moral significanceclaimed for it (see the related entry onconsequentialism). Some opponents of the principle of double effect do indeed deny thatthe distinction between intended and merely foreseen consequences everhas any kind of moral significance.

Nevertheless, many criticisms of the principle of double effect do notproceed from consequentialist assumptions or skepticism about theimportance and moral significance of distinguishing between what anagent intends and what an agent merely foresees. Instead, critics askwhether the principle adequately codifies the moral intuitions at playin the cases that have been taken to be illustrations of it.

4.2 The Problem of Closeness

One important line of criticism is known as the “problem ofcloseness”: it is difficult to distinguish between grave harmsthat are regretfully foreseen as side effects of the agent’smeans and grave harms that are so close to the agent’s meansthat it seems that they must be (regretfully) intended as part of theagent’s means. In theAbortion vs Hysterectomy example,it is hard to see why the death of the fetus would not be aregretfully foreseen side effect of saving the mother’s life inboth cases (Boyle 1991). Or, alternatively, it is hard to see why thedeath of the fetus would not be regretfully intended as part of thephysician’s means of saving the mother’s life in bothcases (Davis 1984, 110). Those who wish to apply double effect to thisexample must provide principled grounds for distinguishing between thecases in this way; no clear resolution of this problem has emerged (asummary of proposals is discussed by Dana Nelkin and Samuel Rickless2015).

4.3 The Side Effect Effect

Are we more inclined to call a harmful result a merely foreseen sideeffect when we believe that it is permissibly brought about, whilealso being more inclined to describe a harmful result as somethingthat was intended as part of the agent’s means when we believethat it is impermissibly brought about? If so, there will be anassociation between permissible harms that are classified as sideeffects and impermissibly caused harms that are classified as resultsbrought about intentionally, but this association cannot be explainedby the principle of double effect. Research by Joshua Knobe (2003,2006) has demonstrated that the ways in which we distinguish betweenresults that are intended or brought about intentionally and thosethat are mere side effects may be influenced by normative judgments insuch a way as to bias our descriptions: we are more likely to say aresult was brought about intentionally when we disapprove of it. Thiswas first pointed out by Gilbert Harman (1976), but is now oftenreferred to as “The Knobe Effect” or “The SideEffect Effect”. Suppose that an agent decided to swerve arunaway trolley away from a track with a rare wildflower on it andonto a track with one track workman on it. Would you say that theagent intended to cause the track workman’s death in order tospare the wildflower? If you would also say that the bystander whoswitches the trolley away from the track with five track workmen on itand onto a track with one track workman on it foresees the death ofthe one as a side effect of saving the five, but does not intend it,then your judgments exemplify the Side Effect Effect. If you believethat it is permissible to swerve the trolley onto the one to save fivebut not permissible to swerve the trolley onto the one to save thewildflower, then this moral judgment influences whether the death ofthe one is intended or a merely foreseen side effect. Does thedistinction between intended and merely foreseen consequences ofaction relied upon by the principle of double effect fail to serve asan evaluatively neutral basis for moral judgments? If so, it mightguide and explain how actions are described without being a reliableguide to evaluating actions.

4.4 Direct and Indirect Agency

Warren Quinn has proposed that what is valuable and correct aboutapplications of double effect could be formulated as involving adistinction between direct and indirect agency. On his view, doubleeffect “distinguishes between agency in which harm comes to somevictims, at least in part, from the agent’s deliberatelyinvolving them in something in order to further his purpose preciselyby way of their being so involved (agency in which they figure asintentional objects), and harmful agency in which either nothing is inthat way intended for the victims or what is so intended does notcontribute to their harm” (1989, p. 343; see also Nelkin andRickless, 2014). Quinn explains that “direct agency requiresneither that harm itself be useful nor that what is useful be causallyconnected in some especially close way with the harm it helps bringabout” (1989, p. 344). He acknowledges that “some cases ofharming that the doctrine intuitively speaks against are arguably notcases of intentional harming, precisely because neither the harmitself (nor anything itself causally very close to it) isintended” (1991, p. 511).

Quinn’s reformulation of double effect is not absolutist incharacter. He observes that a result brought about through directagency might not be impermissible; instead it would require moreoffsetting benefit than the same result brought about through indirectagency in similar circumstances.

Quinn’s proposal would effectively broaden the category ofresults that count as the more problematic form of direct agency incausing harm. As a result, if we believe that some forms of directagency that involve causing death are permissible, we will have toseek some other explanation than double effect’s claim that theharms are indirect or merely foreseen. The soldier who throws himselfon the grenade in order to shield his fellow soldiers from the forceof an explosion has directly involved himself in the protectiveaction. Shelly Kagan (1999, 145) points out that if someone else wereto shove the soldier on the grenade we would certainly say that thatthe harm to the soldier was intended by the person who did theshoving, even if the shoving was intended to promote the goal ofsaving the lives of others. Equally, we should say that it is intendedin this case – not as a goal or as an end pursued for its ownsake but as a means to an end. The same kind of argument can be madefor cases of killing in self-defense when overwhelming and lethalforce is used. If these are cases of permissible direct agency, and ifQuinn is right that the distinction between direct and indirect agencyexplains the intuitive appeal of double effect’s contrastbetween intended means and foreseen side effects, then these casescast doubt on the claim that double effect explains why thelife-saving actions in the Hysterectomy, Heroic Shielding andSelf-defense examples are permissible.

4.5 Does double effect provide an adequate explanation of the trolley cases?

It seems clear to many people that if one were to switch the trolleyfrom a track with five people to a track with only one, the harm tothe one person would not be intended as part of one’s means ofdiverting the trolley from the five to save their lives and wouldtherefore count as a foreseen side effect of swerving the trolley.Quinn’s proposal would not count it as a case of direct agency.These considerations alone do not show that it is justified to switchthe trolley. Double effect might seem to explain the contrastingimpermissibility of pushing someone onto the track in front of thespeeding trolley in order to stop it in order to protect five peoplewho cannot escape on the track ahead. In both scenarios, a personwould be killed as part of one’s plan for saving the five.Because of this, the difference in permissibility might seem to dependon whether the death of that person is a means to saving the five or aside effect of doing so.

Discussions of the Trolley Problem and the relevance of the principleof double effect to explaining our intuition that it is permissible toswerve the trolley can be divided into three groups. First, there arethose who take the paired intuitions in the Trolley Problem as proofof the fundamental role of the distinction between intended means andforeseen side effects in an implicit principle guiding moral judgment(Mikhail, 2011). Second, some argue that it would be wrong for abystander to switch the trolley (Thomson, 2008, contradicting Thomson1976 and 1985) and suggest that people’s willingness to view itas permissible is a result of inadequate reflection. This group wouldinclude those who uphold an absolutist version of the principle ofdouble effect and deny that it provides a permission to swerve thetrolley (Anscombe, 1982). Third, one could reject the claim that theprinciple of double effect could explain the permissibility ofswitching the trolley (McIntyre, 2001), while remaining neutral aboutwhat verdict to render about such artificial cases.

Can our intuitions about the Trolley Problem be generalized to othercases? Autonomous vehicles might be equipped with algorithms thattreat the alleged permissibility of swerving the trolley away from thefive and onto the one as an important precedent. Avoiding dangerouscollisions with other vehicles by swerving onto sidewalks wherepedestrians may or may not be be present might be viewed as ethicallysimilar to swerving the trolley. Or, as Patrick Lin suggests (2016,76–7), an autonomous car driving on a cliffside roadway thatencounters a school bus with many passengers that has moved into itslane as it rounds a sharp corner, might decide to sacrifice itself andits passengers to avoid the more dangerous collision with a school busand the greater predicted loss of life. This should make us allconsider whether the highly abstract and context-less trolley problemelicits reliable moral judgments that can be used as a precedent inprogramming autonomous vehicles (see also discussion of the trolleyproblem and autonomous vehicles in Nyholm and Smids 2016). You, as theBystander at the Switch, have no special positive duty toward the fivethat requires you to assist them, and you have no special negativeduty toward the one that requires you not to harm him. What dutiesdoes an autonomous vehicle have to its driver, other drivers, andnearby pedestrians? Have drivers assumed a risk simply by driving thatpedestrians have not assumed by using a sidewalk? Should thealgorithms promote ethical concerns or the interests of drivers? Whowould buy an autonomous vehicle that would always sacrifice itspassengers to prevent greater loss of life?

4.6 Does Double Effect Explain the Permissibility of Risky Rescues and Rescue by Reducing the Extent of Harm?

Proponents of double effect have argued that agents may cause certainand serious harm or run the risk of causing serious harm when they aretrying to prevent even greater harm that would otherwise be certain tooccur. In such cases, the harm or the risk of harm is described asforeseen by the agent but not intended. Dangerous surgery undertakento save a life is one example (Anscombe 1982; Boyle 1991; Uniacke1998). Uniacke mentions that the distinction between intended andforeseen effects can also be applied to acts of justifiablerisk-taking in which the good effect and the bad effect are“incompatible outcomes”, noting that a parent mightjustifiably throw a child out of a burning building in an attempt tosave its life (1998, s. 3). The parent intends to prevent certaindeath, while foreseeing that the rescue might cause death.

Could it be claimed that the rescuing agents foresaw a risk of causingharm as a side effect of their attempt at rescue but did not intend torisk harm to those they were trying to rescue? Proponents of doubleeffect claim that the physician foresaw but did not intend that thepatient might not survive risky surgery, that the parent foresaw butdid not intend that the child could be killed by the fall, and thatthe soldier foresaw but did not intend to cause his own death (Uniacke1998). But this justification is incomplete for two reasons. First,emphasizing that the risk of causing death isforeseen by therescuer butnot intended by the rescuer implicitly comparesthe rescuer’s motives with the motives of agents who aimed tocause death as an end, out of malice, callousness, or some otherwrongful motive. But double effect speaks only about the contrastbetween harming as a side effect of promoting a good end and harmingas part of one’s means of promoting a good end. Second, thisjustification fails to distinguish between intending to impose a riskof death on a person by acting in a certain way and intending to causedeath. These agents certainly did not intend to cause death, but theydid intend to impose a risk of death on a person by acting in acertain way.

The physician who undertakes dangerous surgery in a patient who wouldotherwise face certain death is attempting to reduce the risk of harmto the patient. Undertaking the risky surgery constitutes thephysician’s means of lowering the patient’s risk of death.The surgery is chosen because it imposes a lower risk of death on thepatient than what the patient faced without it. The surgeon intendedto impose a (lower) risk of death on the patient by undertaking therisky surgery. Given that fact, it is not true that the surgeon didnot intend to impose a risk of harm. Imposing a (lower) risk of harmin order to prevent a greater harm is exactly what the agent intendedto do. This was not a foreseen side effect of action, this was whatconstituted the physician’s attempt to save the patient’slife.

Similarly, the soldier who throws himself on a grenade is attemptingto reduce the extent of the harm that the explosion will cause byattempting to absorb the force of the explosion with his body. Theheroic action is chosen because it imposes a very high risk of harm tohimself, thereby lowering the risk of harm to others nearby. Suchrescues seem to be cases in which agents act permissibly when theychoose to impose a risk of death on someone as their means of loweringthat person’s risk of death (surgery, burning building) or astheir means of lowering the risk of harm to others nearby(self-sacrifice). This involves imposing a risk of harm on a person inorder to promote a good end. It seems that the agents do intend toimpose a risk of harm on the person they involve: that is their meansto the good end. If this is permissible, double effect does not havethe resources to explain why it is permissible, since it is harmful– but justifiably harmful – direct agency. These casessatisfy Warren Quinn’s definition of direct agency as agency inwhich “harm comes to some victims, at least in part, from theagent’s deliberately involving them in something in order tofurther his purpose precisely by way of their being so involved(agency in which they figure as intentional objects),” and theyclearly do not satisfy the definition of harmful indirect agency asagency “in which either nothing is in that way intended for thevictims or what is so intended does not contribute to theirharm” (1989, p. 343). If the risky surgery is unsuccessful andthe patient dies, the surgeon cannot say that what was intended,dangerous but potentially life-saving surgery, did not contribute tothe harm.

4.7 The Role of Conventions and Norms in Warfare

The contrast between the Terror Bomber and the Tactical Bomber isoften viewed as the least controversial pair of examples illustratingthe distinction between intention and foresight that underlies theprinciple of double effect. The judgment that the Terror Bomber actsimpermissibly and the Tactical Bomber acts permissibly is widelyaffirmed. Terror bombing was engaged in by both sides in World War II(see Douglas Lackey (1989) for a thoughtful historical account of thedecision process engaged in by Allied decision-makers and thecontroversy it generated at the time). The view that terror bombing isalways impermissible would condemn the kind of incendiary bombingcarried out by Allied forces in Germany and Japan.

The common judgment that tactical bombing is permissible provided thatit is proportionate also deserves more scrutiny than it usuallyreceives when it is taken to be justified by the principle of doubleeffect. How much of an obligation do military strategists have toavoid harm to civilian populations? This is a substantive issue aboutthe conventions that constrain military decision-making and theprinciples that underlie these conventions. Many relevantconsiderations depend on judgments that are far outside the ambit ofDouble Effect. For example, theRules of Customary InternationalHumanitarian Law displayed on the website of the InternationalCommittee of the Red Cross prohibit attacks targeting civilians. Theyalso include protections designed to minimize harm to civilians:

Rule 15.Precautions in Attack In the conduct of militaryoperations, constant care must be taken to spare the civilianpopulation, civilians and civilian objects. All feasible precautionsmust be taken to avoid, and in any event to minimize, incidental lossof civilian life, injury to civilians and damage to civilianobjects.

Rule 20.Advance Warning Each party to the conflict must giveeffective advance warning of attacks which may affect the civilianpopulation, unless circumstances do not permit.

Rule 24.Removal of Civilians and Civilian Objects from theVicinity of Military Objectives Each party to the conflict must,to the extent feasible, remove civilian persons and objects under itscontrol from the vicinity of military objectives.

These considerations suggest that the principle of double effect doesnot contain, even when the principle of proportionality is included aspart of its content, a sufficient condition of permissibility forbombardment that affects civilian populations. The example sofrequently invoked by philosophers concerning the permissibility oftactical bombing in which civilian deaths are foreseen never mentionsa duty to warn or remove civilians.

5. End of Life Decision-Making

5.1 Pain Relief in Palliative Care

The principle of double effect is often mentioned in discussions ofwhat is known as palliative care, medical care for patients withterminal illness in need of pain relief. Double effect is cited as ajustification for the view that it is permissible to administer opioiddrugs to relieve the suffering of a terminally ill patient, foreseeingthat the hastening of death will occur as a side effect. Double effectreasoning in this context seems to express the compassionate view thatphysicians may not intend to cause the death of a patient, but mayaccept that actions intended to relieve pain might hasten death. Threeassumptions often operate in the background of these discussions:

1. It would be impermissible to administer an opioid drug in a dosehigh enough to hasten the patient’s death in order to cut shortthe suffering of a terminally ill patient in the process ofdying.
2. The side effect of hastening death is an inevitable or at leastlikely result of the administration of an opioid drug in order torelieve the pain of a terminally ill patient.
3. The hastening of death is a not unwelcome side effect of providingpain relief in the context of palliative care.

If the first assumption is not made, double effect has no explanatoryrole to play. Those who appeal to double effect in this context mustalso assume that it would be impermissible to hasten the deathintentionally of a terminally ill patient whom one wastreating with opioids for pain in order to shorten the process ofdying. If one believes that this is permissible, then double effect isnot needed to explain its permissibility.

The second assumption is false. Physicians and researchers haveinsisted repeatedly that it is a myth that opioids administered forpain relief can be expected to hasten death (Sykes and Thorns, 2003provide a review of a large number of studies supporting this claim).There is no research that substantiates the claim that opioid drugsadministered appropriately and carefully titrated are likely todepress respiration. In a survey of research bearing on this issue,Susan Anderson Fohr (1998) concludes: “It is important toemphasize that there is no debate among specialists in palliative careand pain control on this issue. There is a broad consensus that whenused appropriately, respiratory depression from opioid analgesics is ararely occurring side effect. The belief that palliative care hastensdeath is counter to the experience of physicians with the mostexperience in this area.” The mistaken belief that pain reliefwill have the side effect of hastening death may have the unfortunateeffect of leading physicians, patients, and the patients’families to under-treat pain because they are apprehensive aboutcausing this allegedly inevitable side effect.

The third claim – that the hastening of death is not unwelcomein these circumstances – ignores the role of the patient and thepatient’s medical proxy in assessing whether hastening death isa desirable result. It represents the physician’s role as onethat does not require consultation with the patient or thepatient’s proxy or attention to advance directives for guidance.If hastening the death of a patient with a terminal condition isdesirable according to the patient or the patient’s proxy, thenmany thoughtful people would view the first assumption to be false: itwould be permissible to intend to relieve pain while also intending tohasten the death of a terminally ill patient (see Allmark, Cobb,Liddle, and Todd 2010; Kamm 1999; Quinn 1989, 343, n.17; McIntyre2004). On the other hand, if the hastening of death is not desirableaccording to the patient or the patient’s proxy, it is notpermissible to hasten death in the course of treating pain, especiallysince hastening death is neither likely nor inevitable when treatingpain. Patients receiving palliative care whose pain can be adequatelytreated with opioid drugs may well value additional days, hours orminutes of life as they look forward to meetings with family members.A physician’s duty of compassion does not override thepatient’s preferences in such a weighty matter. The apparentlycompassionate assumption that the hastening of death is a desirableresult when a patient is being treated for pain is undulypaternalistic in this context.

Note that if the physician views the hastening of death as somethingthat would be good for the patient, and the patient or thepatient’s proxy agrees, then even a secular version of doubleeffect does not apply to this situation: the hastening of death wouldbe a benefit for the patient, not a harm. As the discussion inSection 1 (Formulations) has shown, any plausibleformulation of double effect would require agents to seek to minimizeor avoid the merely foreseen harms that they cause as side effects. Onthis point, popular understandings of double effect reasoning at theend of life, with the third assumption in place, diverge from what theprinciple assumes: the popular understanding of double effect mightinvolve the assumption that hastening death is a merciful act and nota harm to be avoided.

Note that a variety of substantive medical and ethical judgmentsprovide the justificatory context for this example: the patient isterminally ill, there is an urgent need to relieve pain and suffering,death is imminent, and we can now add that the condition that thepatient or the patient’s proxy consents. The consent of thepatient or the patient’s proxy is not naturally classified as aconcern with proportionality, understood as the physician’sweighing of harms and benefits.

5.2 Terminal Sedation

In a U.S. Supreme Court decision that rejected arguments forpermitting patients with terminal illness to request assistance from aphysician in ending their lives (Vacco et al. v. Quill et al., 117S.Ct. 2293 (1997), Chief Justice William Rehnquist, writing for themajority, invoked double effect not only as a justification for theadministration of pain-relieving drugs that might hasten death butalso as a justification for the practice known as terminal sedation orcontinuous sedation. This occurs when patients with terminalconditions who experience intractable pain that cannot be treatedeffectively with opioid or other analgesic drugs are treated withsedative drugs (which do not typically have analgesic properties) inorder to induce unconsciousness. Artificial hydration and nutritionare not provided for patients sedated for these reasons in the contextof palliative care at the end of life. If death is not alreadyimminent for such a deeply sedated patient, dehydration and starvationwill make it inevitable. In such cases, withholding life-sustainingtreatment does in fact hasten death, intentionally but justifiably.Prolonging the process of dying for a continuously sedated patient, inwhom sedation was initiated to deal with intractable pain, does notbenefit the patient.

In some cases, the patient’s right to refuse life-sustainingtreatment, as expressed directly by the patient or through a proxy oran advance directive, is the justification for withholding artificialhydration and nutrition during terminal sedation. If a dying patientviews hastening death as a good to be pursued, then doubleeffect’s presumption that death is a harm that a physician maynot intend to bring about is at odds with the preferences of a patientwho rejects artificial hydration and nutrition in order to hastendeath.

Timothy E. Quill, M.D., Rebecca Dresser, J.D, and Dan W. Brock, Ph.D.argue that double effect, if applied consistently, would rule out thepractice of terminal sedation. “Unlike the use of high-doseopioids to relieve pain, with death as a possible but undesired sideeffect, terminal sedation inevitably causes death, which in many casesis what the patient desires. Although the overall goal of terminalsedation is to relieve otherwise uncontrollable suffering,life-prolonging therapies are withdrawn with the intent of hasteningdeath. Terminal sedation would thus not be permitted under the rule ofdouble effect, even though it is usually considered acceptableaccording to current legal and medical ethical standards”(Quill, Dresser and Brock, 1997; see also Quill, Lo and Brock1997).

The belief that doctors can cite double effect reasoning to justifyactions that hasten death tends to obscure rather than clarify theseimportant issues in palliative care. A single principle is nosubstitute for the professional expertise of palliative carespecialists who seek to ensure a patient’s comfort at the end oflife by using a variety of forms of care while respecting thepatient’s right to refuse even life-sustaining treatment.Standardized forms that invite patients with advanced chronicillnesses to specify in advance theirMedical (or Physician)Orders regarding Life-Sustaining Treatment (MOLST or POLST form)allow patients to request or to reject various treatments that wouldextend their lives while also opting for forms of medical care thatwill promote their comfort in dying (Bomba 2011). A physicianproviding palliative care with the goal of promoting thepatient’s comfort might provide pain relief, supplemental oxygenor artificial hydration to a patient with the goal of increasing theircomfort, even when these treatments also have the effect of extendinglife and prolonging the process of dying. The issues are complex andcannot be resolved with a single principle that endorses a singleremedy. The compassionate ethos that the traditional application ofdouble effect is often understood to express is a central commitmentof palliative care, but the considerations to be taken into account gobeyond what could be explained by the principle of double effect.

6. One principle or many loosely related exceptions to a general prohibition on causing grave harms?

It is not at all clear that all of the examples that double effect hasbeen invoked to justify can be explained by a single principle, sincethere may be a variety of considerations that bear on thepermissibility of causing grave harms in particular contexts. Perhapsall of these cases have in common the feature that the agent acts topromote a good end in a permissible manner and regrets any harms thatare involved. For some proponents of double effect, these facts areenough to show that the harms that are caused should be described asmerely foreseen side effects.

Critics of the use of double effect as an explanatory principle pointout that the proportionality condition is vague and too general,requiring only that the good effect outweigh the foreseen bad effector that there be sufficient reason for causing the bad effect. Thesecritics add that when substantive principles that explain thepermissibility of causing the kind of harm in question are explicitlyformulated, these principles are doing all of the justificatory work(Davis 1984; McIntyre 2001). These substantive considerations are notderived from double effect and in some cases do not support thetraditional applications of double effect. If this criticism iscorrect, then perhaps the cases that have traditionally been cited asapplications of the principle of double effect are united only by thefact that each is an exception to the general prohibition on causingthe death of a human being.

The historical origins of the principle of double effect as a tenet ofCatholic casuistry might explain the appearance that there is a singleprinciple with diverse applications. If one were to assume that it isabsolutely prohibited to cause the death of a human being, then itwould be impermissible to kill an aggressor in self-defense, tosacrifice one’s life to protect others, to hasten death as aside effect of administering sedation for intractable pain, toendanger non-combatants in warfare, to undertake risky surgery to savea patient’s life, to perform a hysterectomy on a pregnant womanin order to save her life, or to swerve the trolley. However, if onewere to assume instead that what is absolutely prohibited is to causethe death of a human beingintentionally, then these casescan be viewed as cases in which one might permissibly cause deathregretfully viewing the death as a “merely foreseen sideeffect” of pursuing a good end.

However, as we have seen, it is hard to make sense of the idea thatthe soldier who throws himself on a grenade does not view hisself-sacrifice as a means of protecting his fellow soldiers, or thatthe physician who performs a hysterectomy on a pregnant woman does notsee the removal of the fetus as part of the life-saving procedure. Itis true that we could emphasize the soldier’s motive by talkingabout what he intended: that his intention was not to cause his owndeath but to protect the lives of his fellow soldiers, or that thephysician who performs a hysterectomy on a pregnant woman to save herlife did not intend to kill the child, only to remove a cancerousuterus containing a fetus. But in the same way we could say of someonewho ended her life: her intention was not to kill herself but to bringher suffering to an end; and of someone who killed an enemy hesuspected of plotting against him that the did not intend to kill theenemy but instead intended to insure his own future security. This wayof speaking amounts to saying that the harm that the agent caused waschosenas a means to the agent’s end and was notpursued for its own sake. But double effect is supposed to condemn,not to justify, grave harms intended as a means to a good end.

Some have developed this kind of criticism by arguing that the appealof the principle of double effect is, fundamentally, illusory: anagent’s intentions are not relevant to the permissibility of anaction in the way that the proponents of the principle of doubleeffect would claim, though an agent’s intentions are relevant tomoral assessments of the way in which the agent deliberated (seeMcCarthy 2002; Scanlon 2008). That an agent intended to bring about acertain harm does not make an otherwise permissible actionimpermissible, but it can explain what is morally faulty about theagent’s reasoning in pursuing that line of action.

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Other Internet Resources

• List of References for the Principle of Double Effect [PDF], maintained by Jörg Schroth.
• Whether it is lawful to kill a man in self-defense?, St. Thomas Aquinas,Summa Theologica, Second Part of theSecond Part, Question 64, Article 7.
• Just War Theory, Internet Encyclopedia of Philosophy.
• The Rules of Customary International Humanitarian Law, International Committee of the Red Cross.
• U.S. Supreme Court decisionVacco v. Quill, concerning the challenge to laws prohibiting assisted suicide posedby Quill,et al., Legal Information Institute, Supreme CourtCollection.
• The International Association for Hospice and Palliative Care.

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