Scott D. Sagan, Stanford University Benjamin A. Valentino

Transcription

JUST A WAR THEORY?
AMERICAN PUBLIC OPINION ON ETHICS IN MILITARY COMBAT
Scott D. Sagan, Stanford University
Benjamin A. Valentino, Dartmouth College
ABSTRACT: To what extent are the American public’s views on the use of force consistent with just
war doctrine’s ethical principles? Drawing on an original survey experiment conducted on a
representative sample of American citizens, we examine American attitudes towards the jus in bello
principles of proportionality, due care and distinction. Consistent with the moral logic of the
principle of proportionality, we find evidence that Americans are less willing to inflict collateral deaths
on foreign civilians when the military advantage derived from destroying a target is lower. We also
find that most Americans are willing to risk of the deaths of some American soldiers to avert a larger
number of collateral Afghan civilian deaths, which broadly accords with the principle of due care.
Nevertheless, we find that the public’s commitment to proportionality and due care is heavily biased
in favor of protecting American lives and national security interests in ways that suggest only limited
support for traditional interpretations of just war theory. Moreover, we find little evidence that the
public supports the principle of distinction (non-combatant immunity). Under certain conditions,
more than two-thirds of the American public was willing to approve of intentional attacks on foreign
civilians, and support for large scale killing of civilians did not decrease when the attacks were labeled
as intentional with a strategic justification. In addition, contrary to prevailing interpretations of just
war doctrine, Americans were significantly more likely to accept the collateral deaths of foreign
civilians when those civilians were described as politically sympathetic with the adversary than when
they were described as political opponents.
The authors would like to thank Benjamin Buch, Jonathan Chu and Anna Coll for their
indispensable research assistance on this project. We also thank Seth Lazar, Rachel Stein, David
Traven and Allen Weiner for helpful comments on earlier versions of this article.
03/24/2015 DRAFT: PLEASE DO NOT CITE OR
CIRCULATE WITHOUT PERMISSION OF AUTHORS
Introduction
The philosophical and legal doctrine known collectively as “just war doctrine” or “just war
theory” is widely acknowledged as the most influential source of ideas about the ethics of war, at
least in Western societies (Walzer 2004, Orend 2008). Its principles have been the prime focus of
scholarly debate about the ethics of war in the West since its central tenets were first codified by
Christian theologian and philosopher St. Augustine in the late fifth century. Just war doctrine also
provides the basis for most extant international humanitarian law governing the conduct of war
(Roberts and Guelff 2004) and has directly influenced the U.S. military’s official targeting doctrine
(Joint Chiefs of Staff 2013, Kahl 2007). Just war principles are frequently cited, explicitly or
implicitly, in public debates by both proponents and critics of the use of force to justify their
respective positions.
Despite the indisputable influence just war doctrine has exerted on the discourse of war
among elite jurists, scholars and politicians, however, we know almost nothing about the extent to
which the American public’s views on the use of force are consistent with just war philosophy.1 Yet
it is far from self-evident that the public’s views of the ethics of war closely correspond to just war
principles. Needless to say, most Americans have not studied Grotius or Michael Walzer. Even if
they had, as most proponents of just war doctrine acknowledge, the doctrine provides a normative
framework for how statesmen and soldiers should act when deciding to use force or when engaged in
war, but does not seek to describe how they actually act. Equally important, just war doctrine offers
only general guidelines to guide thinking about the use of force. Using the common legal
terminology, just war doctrine provides general standards (“do not drive recklessly”) rather than
bright line rules (“do not drive above 55 mph”) (Wiener, 2006). Just war doctrine, for example,
requires that the use of force should be a last resort, but it provides no simple formula that leaders
or the public could use to ascertain exactly when that line has been crossed. Just war doctrine
similarly maintains that soldiers and statesmen should not use force in a manner in which the
collateral damage to non-combatants is “disproportionate” to the military benefits of the attack, but
it provides no strict guideline for how to measure proportionality or disproportionality. Just war
doctrine therefore leaves ample room for individual judgment and interpretation, but we have
almost no information to help us understand how most people interpret just war principles in
For an exploration of Israeli attitudes on just war theory, focusing primarily on just war theory’s assertion of the “moral
equivalence of soldiers” see Benbaji, Falk, and Feldman 2014.
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practice. As Walzer (1977, 130) writes, just war principles “don’t explain the most critical of
judgments we make of soldiers and their generals. If they did, moral life in wartime would be a great
deal easier than it is.” Furthermore, although many of just war doctrine’s central tenets – like the
requirement of having a “just cause” for war – likely coincide with the public’s common sense
morality of self-defense, others, like the “doctrine of double effect,” are more subtle and
controversial, and may be less widely accepted by members of the public, even if they understood
them completely.
Because just war theory is principally a normative doctrine, whether or not public views on
the use of force correspond to just war doctrine should not be regarded as a test of the theory’s
validity as a moral doctrine. Understanding the extent to which the public has internalized just war
principles, however, is important for at least three reasons. First, even for purely normative
scholars, identifying discrepancies between normative prescriptions and our moral intuitions is
important because such discrepancies may signal a potential flaw in the normative theory or, at a
minimum, require further elucidation (Audi 2005). In this regard, our investigation can be viewed as
part of the growing body of scholarship that straddles the line between normative theory and
empirical research and seeks to describe and understand the origins of our moral instincts (Green
2013; Haidt 2012). Second, understanding how the public thinks about the ethics of war provides
insights into how warfare is likely to be practiced in the real world because, at least in democratic
states, the public exerts an important influence over government policies. In turn, understanding
how the public interprets and applies just war principles may provide some indication of whether
these principles provide any practical limits on war. Third, for normative theorists of war who
desire to see certain prescriptive principles implemented in practice, understanding public attitudes
on the ethics of war should also help identify the areas in which the public’s views differ from those
principles and, potentially, what kinds of arguments might be most effective in changing those
views.
Just war doctrine encompasses a large and diverse set of ethical arguments and legal
precepts. It is not possible to explore all of them in any single paper. We choose to focus on the
public’s acceptance of three key moral principles of jus in bello, the body of doctrine that governs the
conduct of war. These principles are usually referred to as “distinction” (sometimes called
“discrimination” or “non-combatant immunity”), which concerns the killing of non-combatants;
“proportionality,” which asks military decision makers to weigh the costs to foreign civilians of a
particular operation against the operation’s contribution to winning the war; and “due care” which
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requires that combatants try to minimize collateral damage, including accepting some risk to
themselves if necessary. Debates over competing interpretations of these principles remain among
the most frequent topics in the literature on the ethics of war and often lie at the center of public
discourse about the use of force in the contemporary world.
We explore the American public’s views on distinction, proportionality and due care using
data collected from three original survey experiments. In each experiment we asked subjects to read
a short, hypothetical news story about an American decision to use force against Taliban targets in
Afghanistan. The stories were designed to highlight the kinds of moral choices implicated by the
principles of distinction, proportionality and due care. By holding most facts about the scenario
described in the story constant while manipulating a single feature of the situation relevant to the
application of just war doctrine, we can isolate the effect of varying the degree of distinction,
proportionality or due care on each subject’s approval of the use of force.
We report three main findings. First, we find evidence that the American public accepts the
general moral logic of the principles of proportionality and due care. They are more likely to
approve the use of force and accept higher levels of collateral civilian deaths when the military
advantage of destroying the target is greater. Most Americans are willing to accept the risk of the
deaths of some American soldiers to avert larger numbers of collateral Afghan civilian deaths, which
broadly accords with the principle of due care. In these ways, just war theory appears to be more
than just a prescriptive theory of how people ought to behave; it describes the moral choices the
public claim they would actually make about the use of force. Second, however, we find that the
American public’s conceptions of proportionality and due care are heavily biased in favor of
protecting American lives and national security interests in ways that suggest at best limited support
for most interpretations of just war doctrine. Forty-four percent of the public, for example,
supported a U.S. military strike against an explicitly “low level” Taliban target that would have “little
effect on the outcome of the war” even though the strike was estimated to kill 200 civilians. The
public’s tolerance for risk to American soldiers in order to protect foreign noncombatants is also
relatively low. When presented with a choice between two military operations, one of which would
entail greater risks for American soldiers but kill fewer foreign civilians and one of which would limit
risks to American troops but kill more foreign civilians, a large majority of the public preferred to
limit the risks to U.S. troops even when the number of civilians killed was four times greater than
the number of U.S. troops who would have died in the risker operation. Third, we found that the
public’s attitudes regarding the principle of distinction deviated substantially from just war doctrine.
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In some conditions, more than two-thirds of the American public was willing to approve of
intentional attacks on foreign non-combatants. The public was also significantly more likely to
accept the deaths of foreign civilians when those civilians were described as politically sympathetic
with the adversary than when they were described as political opponents, a position which does not
conform to principles of traditional just war doctrine.
The remainder of this paper is divided into five main sections. In the first section we review
the principles of distinction, proportionality and due care in just war doctrine and derive from them
several testable hypotheses about public attitudes towards the use of force. The second section
describes our research methodology for evaluating these hypotheses. In the third section we report
the empirical findings of our survey experiments. The fourth section discusses the broader
significance of those findings. A final section explores some implications of our research for
scholarship and policy.
The Principles of Distinction, Proportionality and Due Care in Just War Theory
In this paper we explore American attitudes towards three principles of jus in bello, just war
doctrine’s guidelines for waging a just war. These principles are usually referred to as distinction,
proportionality and due care.2 Simply put, the distinction principle states that military forces may
never intentionally target non-combatants. The proportionality principle argues that the harms
caused by the use of force must be proportional to the expected benefits of using force. Some
scholars also identify a third principle, which figures prominently in international humanitarian law,
called “due care” or “precautions in attack.” This principle requires armed combatants take
“feasible measures” to avoid killing civilians, even if it means accepting some risk to themselves.
Distinction
We do not directly examine the jus in bello principle of “necessity.” The principle of necessity means different things to
different practitioners and scholars. For example, in April 2012 Obama Administration official John O. Brennan took a
minimalist view when stating that U.S. “targeted strikes conform to the principle of necessity, the requirement that the
target have definite military value.” (Brennan, 2012) Others argue that the principle of necessity requires that attackers
choose the means of attack that causes the minimum amount of harm necessary to eliminate a particular threat. For
reviews and critical discussions of the logic of the necessity principle see Lazar (2012) and Statman (2011). Previous
experimental studies, have demonstrated that, all else equal, the American public is less likely to approve the use of force
when foreign civilian casualties are higher (Gelpi, Feaver and Reifler 2009, 256; Press, Sagan and Valentino 2013).
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The notion that civilians should be spared the violence of war is one of the oldest rules of combat
(Kinsella 2011; Slim 2008; van Dongen 1991; Lind 2014). As Michael Walzer notes, one nearly
universal rule of warfare points “toward the general conception of war as a combat between combatants,
a conception that turns up again and again in anthropological and historical accounts [emphasis
original]” (Walzer 1977, 42). Like many just war precepts, the principle of distinction is deceptively
simple. As codified in the Geneva Conventions, the principle requires that “persons taking no
active part in the hostilities . . . shall in all circumstances be treated humanely” and prohibits
“violence to life and person, in particular murder of all kinds” (quoted in Roberts and Guelff 2004,
302). Article 48 of the 1977 Additional Protocol I to the Convention further provides that
combatants “shall at all times distinguish between the civilian population and combatants… and
accordingly shall direct their operations only against military objectives” (quoted in Roberts and
Guelff 2004, 447). The U.S. military’s formal targeting doctrine also clearly specifies that “purely
civilian/protected objects or locations may not be intentionally targeted” (Joint Chiefs of Staff 2013,
A-2).
The general imperative that civilians should be immune from intentional attack during times
of war is widely accepted by nearly all just war scholars and jurists, although there is disagreement as
to the underlying moral justifications for the prohibition (see Fabre 2009; Arneson 2006; Carpenter
2005).3 Nevertheless, there has been considerable debate about the precise meaning of the term
“non-combatant,” which has significant implications for the practical application of this principle.
Most just war theorists agree that at least some individuals who are neither armed, nor
members of a formal military organization still may be legitimate targets of attack if they contribute
directly and significantly to the adversary’s war effort. Civilian mechanics and technicians who
repair military equipment or workers in munitions factories, for example, are often cited as possible
exceptions to the strict prohibition on targeting civilians. As Hugh Trenchard, Chief Marshall of the
British Royal Air Force during the inter-war years famously asked, “Why should the person who
made the gun be less a target than he who fired it?” (quoted in Grayling 2006, 133). The Geneva
Conventions prohibit attacks against civilians “unless and for such time as they take a direct part in
hostilities” (quoted in Roberts and Guelff 2004, 448).4 Walzer (1977, 145-6) reasons that
For partial exceptions to the general consensus on strict non-combatant immunity from just war doctrine “revisionists”
see Frowe 2014; McMahan 2009; and Overland 2005. For a review of the arguments of some dissenters from just war
theory’s conception of distinction, see Fellmeth 2008.
4 The 1977 Geneva Protocol II, which applies to non-interstate conflicts, uses identical language.
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We try to draw a line between those who have lost their rights because of their
warlike activities and those who have not… The relevant distinction is not between
those who work for the war effort and those who do not, but between those who
make what combatants need to fight and those who make what they need to live, like
all the rest of us. When it is militarily necessary, workers in a tank factory can be
attacked and killed, but not workers in a food processing plant. . . .
Although scholars in the just war tradition debate precisely where the line between civilian and
combatant lies, most agree that the key moral distinctions rest with how large and direct a contribution
civilians make to the war effort (Rodin 2008). When civilians’ contributions are small and infrequent,
halting these contributions usually does not justify lethal force. When their contributions are indirect,
even if they are significant, they can ordinarily be addressed with means other than military force. As
such, most proponents of just war doctrine and the laws of armed conflict concur that factors such as
civilians’ nationality or mere political sympathy with the adversary are not sufficient on their own to
revoke civilians’ immunity from attack since the activities of regular citizens or even political
supporters do not constitute a significant and direct contribution to the war. As Walzer succinctly
puts it, “the structure of rights stands independently of political allegiance” (1977, 158).
To the extent, therefore, that American public’s views on the use of force are consistent with
the principle of distinction, the foregoing discussion suggests the following three hypotheses:
Hypothesis 1: Americans should decrease their support for military operations that intentionally
target foreign civilians.
Hypothesis 2: Americans should increase their support for military operations that intentionally
target foreign civilians the more significantly and directly those civilians contribute to the
adversary’s war effort.
Hypothesis 3: Whether or not foreign civilians politically support or oppose U.S. adversaries
should have no independent effect on the willingness of Americans to support military
operations in which foreign civilians are killed intentionally or unintentionally.
Proportionality: Military Advantage
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The principle of proportionality constitutes the second major tenet of jus in bello that we examine in
this paper.5 In the broadest terms, the proportionality principle requires that the harms of any
military attack be outweighed by its benefits (Walzer 1977, 129-133; Hurka 2005). The harms and
benefits can include almost any consequences of an attack, but much of the discussion among just
war theorists has focused on the question of how to weigh the harm of unintended foreign civilian
casualties against the contribution of the attack to winning the war.6
In international law, the proportionality principle compares expected collateral damage to
the expected “military advantage” of an attack. The 1977 Additional Protocol I to the Geneva
Conventions, for example, prohibits “any attack which may be expected to cause incidental loss of
civilian life, injury to civilians, damage to civilian objects, or a combination thereof, which would be
excessive in relation to the concrete and direct military advantage anticipated” (quoted in Roberts
and Guelff 2004, 453). The principle of proportionality is also reflected explicitly in the U.S.
military’s official weapons targeting doctrine.7
Although the principle of distinction strictly forbids the intentional targeting of civilians just
war theory permits even the foreseeable killing of civilians during attacks on military targets, as long
as certain additional conditions are satisfied.8 These conditions constitute the “doctrine of double
effect” and are central to the application of proportionality in the real world.9 According to Walzer
(1977, 153), attacks on military targets that are expected to result in “collateral” civilian deaths must
meet four key criteria to be permissible under traditional interpretations of the “doctrine of double
effect.” First, the attack on the military target must be a legitimate act of war. Second, the direct
effect of destroying the military target must be morally acceptable. Third, the attacker must have the
intention only of destroying the military target, killing civilians may not be a deliberate objective or an
indirect means to achieve a legitimate objective. Finally, the good intended effects of destroying the
Proportionality is also a condition for jus ad bellum – which requires that leaders should not embark upon war unless
they determine that destructiveness of the war will be outweighed by the good effects the war will achieve. Previous
experimental studies, suggest that, all else equal, the American public is less likely to approve the use of force both with
respect to starting wars and with respect to specific combat operations foreign civilian casualties are higher (Gelpi,
Feaver and Reifler 2009; Press, Sagan and Valentino 2013).
6 It is not clear whether or how the proportionality principle applies to adversary soldiers. As David Hurka (2005, 58)
argues “In bello proportionality as standardly understood seems to allow a nation to kill virtually any number of enemy
soldiers to save just one of its own soldiers this claim mirrors one from the morality of self-defense, where a person may
kill any number of attackers if that is necessary to save his own or another’s life …”
7 The Joint Chiefs of Staff Joint Doctrine for Targeting states that “collateral damage to civilian objects or persons must not
be excessive in relation to the concrete and direct military advantage expected to be gained” (Joint Chiefs of Staff 2013,
A-5).
8 The U.S. military adopts similar guidelines.
9 For arguments against the doctrine of double effect see Kamm 2004 and Otsuka 1994.
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legitimate military target must outweigh the unintended bad effects of killing the civilians. In other
words, the attack must be proportional.
In practice, the third and fourth criteria have produced the most academic and legal
disputation. Many scholars have questioned what it means for combatants not to have the intention
of killing civilians even if they are certain that civilians will die in an attack anyway (McKeogh 2002;
Conway-Lanz 2006; Crawford 2013). Others have asked how many civilians is it permissible to kill
unintentionally in the service of particular military goals and how much risk to the success of the
mission attackers must accept to minimize civilian deaths (Hurka 2005; Bohrer and Osiel 2013;
Porat and Bohrer 2014). Despite these differences, however, there is widespread agreement among
just war theorists that, all else equal, the greater the military importance of the target, the greater the
number of collateral civilian deaths that may be permitted in destroying it.
Hypothesis 4: Americans should increase their willingness to accept collateral deaths among foreign
civilians the greater is the military advantage of destroying the target for the outcome of the war.
Due Care
Some scholars of just war theory also identify a separate principle of “due care,” which
focuses on the question of how much personal risk soldiers should be expected to assume in order
to reduce the risk that military operations might kill or injure foreign civilians or civilian property.10
In international law, the principle is related to “precautions in attack.” Article 57 of the 1977
Additional Protocol I to the Geneva Convention stipulates that, “in the conduct of military
operations, constant care shall be taken to spare the civilian population, civilians and civilian
objects,” (quoted in Roberts and Guelff 2004, 452) though it does not specify whether soldiers
should take risks themselves to provide constant care.
The principle of due care emerged from the concerns of some just war theorists that the
principles of proportionality and distinction alone are too permissive, allowing soldiers to too easily
inflict collateral damage when targeting legitimate military targets by claiming that the damage was
unintentional and less than the benefits of destroying the target. Because soldiers are trained and
expected to assume risks during times of war, the due care principle requires that combatants
10
Seth Lazar (2012) argues that due care is better understood as part of the broader principle of necessity.
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willingly shoulder at least some risk in order to minimize risk to non-combatants (Margalit and
Walzer 2009).11 As Walzer (1977, 155-6) writes,
simply not to intend the deaths of civilians is too easy; most often under battle conditions,
the intentions of soldiers are focused narrowly on the enemy. What we look for in such
cases is some sign of a positive commitment to save civilian lives. Not merely to apply the
proportionality rule and kill no more civilians than is militarily necessary... Civilians have a
right to something more. And if saving civilian lives means risking soldier’s lives, the risk
must be accepted… Exactly how far they must go in doing that is hard to say… It is best, I
think, to say simply that civilians have a right that “due care” be taken.”12
David Luban concurs that the laws of war “never explicitly address the question of how
much risk soldiers must assume to minimize ‘collateral’ civilian casualties. International
humanitarian law requires soldiers to do everything feasible to avoid unintended civilian casualties,
but it never defines ‘feasible’” (Luban 2014, 279). Luban terms the ratio of acceptable foreign
civilian deaths to one’s own military deaths the “risk transfer ratio” (Luban 2014, 279). Scholars and
international lawyers disagree about what value the risk transfer ratio should take or what additional
considerations should affect the balance. Some, like Asa Kasher and Amos Yadlin (2005), argue that
combatants have a right to weigh the lives of their own soldiers more highly than the lives of foreign
civilians, suggesting a risk transfer ratio greater than one. Others, like Thomas Hurka (2005, 64),
argue that “our soldiers’ and enemy civilians’ lives count roughly equally. While a nation may prefer
its own civilians’ lives to those of enemy civilians, it may not do the same with its soldiers’ lives.
Instead, it must trade those off against enemy civilians’ lives at roughly one to one.”13 Still others,
including Avishai Margalit and Walzer (2009), argue that “By wearing a uniform, you take on
yourself a risk that is borne only by those who have been trained to injure others... You should not
shift this risk onto those who haven’t been trained, who lack the capacity to injure.” As such, they
assert, soldiers must bear a greater burden of risks than civilians and soldiers should be instructed to
Although the principle of providing due care to protect civilians is usually seen as a special moral duty for professional
soldiers, in practice it can also be linked to the principle of proportionality. After all, when soldiers assume greater
personal risks to themselves in order to protect adversary or neutral civilians, they can increase the costs of the war to
their own side and reduce, at least to some extent, their chances of successfully completing their mission and thus
contributing to winning the war. These costs to the war effort presumably must be weighed against the costs of
collateral damage according to the principle of proportionality.
12 See also Lee (2012, 213).
13 For a similar argument see Dunlap (2000).
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“conduct your war in the presence of noncombatants on the other side with the same care as if your
citizens were the noncombatants.”14 This implies a risk transfer ratio of less than one.
Although these disagreements are significant, there is a broad consensus among scholars in
the just war tradition that states have the right to impose at least some risks on foreign civilians
(keeping in mind that civilians may never be intentionally targeted) in the effort to reduce the risks to
their own soldiers. The exact value of the risk transfer ratio remains disputed, but most just war
theorists would probably accept that military commanders should be permitted to launch an airstrike
against an important enemy military base if doing so would save 1,000 soldiers from dying if the
base had to be attacked by a ground assault – even if the airstrike was expected to kill one civilian
who happened to be visiting the base. Conversely, most just war theorists would probably reject the
attack if it would avert the death of a single soldier but cause the deaths of 1,000 foreign civilians.
If the public accepts the underlying logic of due care, therefore, this suggests the following
related hypotheses:
Hypothesis 5: Americans should be willing to risk the lives of some U.S. soldiers to prevent
collateral deaths of foreign civilians in U.S. military operations.
Hypothesis 6: Americans should increase their willingness to accept collateral deaths among foreign
civilians in U.S. military operations the greater the number of U.S. soldiers’ deaths that will be
averted by such operations.
Research Design
Perhaps the most obvious way to explore public attitudes about the ethics of war would be
to draw upon data from existing public opinion polls on actual military operations to gauge public
support for various forms of military action (for example, see Eichenberg 2005). Over the past 30
years, numerous polls have inquired about the public’s views on the killing of foreign civilians in
various conflicts and whether American soldiers should take more or less risks to protect those
civilians. Unfortunately, most public opinion polls suffer from two common problems that severely
limit their utility in understanding public attitudes about just war theory principles. First, very few
poll questions are specified clearly enough to identify views about these specific principles. A 2011
Luban adopts a similar position, arguing that we have an obligation to “treat civilians on the other side in a way that
would be minimally acceptable even if they were our own” (Luban 2014, pp?). See also Christopher (1999).
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poll conducted by Gallup, for example, found that 49% of Americans agreed that it was “sometimes
justified” “for the military to target and kill civilians” (Gallup 2011).15 The question, however, did
not define the word “civilian” (e.g., whether civilians referred to munitions workers or children or
both), nor did it specify the purpose of the killing (e.g., would the civilians be targeted with the
intent to kill them or because they were collocated with legitimate military targets) or whether killing
those civilians might avert even greater harms to other civilians. Yet as described above, the answers
to these questions are critical for the application of just war doctrine.
Polls that focus on public attitudes about specific military operations in the real world also
face a second limitation. For example, a CNN poll conducted in July 2014 found that 55% of
Americans believed that “the amount of military force that Israel has used in Gaza against Hamas
and the Palestinians” had been either about right or too little, compared to 39% who said Israel had
used “too much” military force (CNN/ORC 2014). In comparison, a poll taken in April 2003, 87%
of Americans indicated that they believed that the United States had used the right amount or too
little force in Iraq, with only 6% saying we used too much (CBS 2003). Despite the clear differences
in responses, however, it is not possible to infer from these two polls whether Americans believed
the war in Iraq was more proportionate than Israel’s war against Gaza. Direct comparisons of this
kind are confounded by the influence of countless case-specific factors that distinguish the conflicts
(e.g., the different interests at stake, differences in public attention to the two wars, the different
means of military forces used, etc.). As a result, we cannot use this information to determine which
factors have the greatest impact on the public’s assessments of the ethics of the use of force.
To test the hypotheses above, therefore, we chose to conduct three related survey
experiments on a large, representative sample of American citizens over the age of 18. Unlike public
opinion data drawn from real-world instances of the use of force, a survey experiment allows us to
construct a hypothetical scenario in which we can hold most relevant facts about the scenario
constant (e.g., the broader conflict context, the effectiveness of using force, or the kinds of weapons
used) while varying only one aspect of the situation (e.g., the ratio of foreign civilian to U.S. military
deaths, the “culpability” of potential civilian victims, whether the killing of civilians was intentional
or not, or the military importance of the target). This design enables us to isolate the effects of
distinction, proportionality, due care on public attitudes about the use of force.
15
U.S. support for targeting civilians was the highest among all 131 countries polled.
11
To conduct this survey we contracted with YouGov, an internet polling and experimental
research firm. YouGov utilizes a technique called “sample matching” to approximate a representative
sample. This sampling technique is still relatively new compared to traditional equal probability
random sampling, but it is becoming increasingly popular for use in academic research applications,
and its performance has been shown to meet or exceed that of surveys based on more traditional
telephone polling techniques (Berrens et al. 2003; Sanders et al. 2007; Yeager et al. 2011; Ansolabehere
and Schaffner 2014)
We devised three separate experiments with a total of 12 experimental conditions (five
conditions in experiment 1, four conditions in experiment 2 and three conditions in experiment 3),
each focusing a different aspect of just war theory. In each experiment, subjects were randomly
assigned to read a different news story about a hypothetical U.S. military crisis in Afghanistan.
Approximately 150 subjects were assigned to each condition. Subjects were told to read the story
carefully and urged to “imagine how you would feel about these events if they were happening in the
real world today.” To increase the realism of the experience, the stories were constructed to look
like typical newspaper stories with an Associated Press byline. The key elements of each of the three
experiments are summarized in Table 1. The full stories are included in the appendix at the end of
this paper.
We chose to focus our stories on the conflict in Afghanistan since it was the most significant
ongoing American military operation at the time the survey was administered. We believe this
maximizes the external validity of the experiment and makes a direct contribution to contemporary
policy debates. Of course, because all of our scenarios are drawn from the Afghan war, we cannot
explore whether or how specific features of the Afghan conflict affect our findings and, therefore,
whether American attitudes about just war principles might vary in different conflicts. Perhaps the
most significant concern in this regard is the public’s relatively low support for the war in
Afghanistan in 2014. Indeed, averaging across all our conditions, 68% of respondents said they
“opposed” the war in Afghanistan. Similarly, a poll administered by the Pew Research Center in
January 2014 reported that 52 percent of Americans had already concluded that the U.S. had
“mostly failed in achieving its goals in Afghanistan” with only 37% saying it had mostly succeeded.16
It is difficult to say how these dynamics might affect our findings. On the one hand, the perception
of failure in Afghanistan might make the public less willing to inflict civilian casualties there, since
16
http://www.people-press.org/2014/01/30/more-now-see-failure-than-success-in-iraq-afghanistan/2/
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Americans may conclude that doing so is unlikely to help win an unwinnable war. On the other
hand, perhaps Americans have become desensitized to civilian deaths in Afghanistan or are more
willing to inflict casualties in the hope of snatching a victory from the jaws of defeat.
Afghanistan also differs from many other conflicts because most Afghan civilians are not
clearly allied with America’s adversary, the Taliban insurgents, and much of the official rhetoric
justifying the war has focused on improving the lives of Afghan civilians. This seems likely to
decrease tolerance for civilian casualties compared to classic interstate wars, in which foreign
civilians are often presumed to be supporters of the adversary’s government. Future research could
explore the interaction of these or other factors and attitudes towards killing foreign civilians.
Nevertheless, because the conflict in Afghanistan remains America’s longest and most significant
ongoing war, we believe it represents a highly relevant place to explore public attitudes about the use
of force.
In each story in our experiment, subjects read that the United States had identified a Taliban
target in an Afghan village and was considering various options to attack it. Across all three
experiments we attempted to describe legitimate military targets that most Americans would agree
constituted a threat, but not such a critical threat that it might justify the invocation of “supreme
emergency,” which some scholars have argued might justify an exemption from just war principles.17
Experiment 1, which we refer to as the “distinction/culpability experiment,” was designed to
examine views about the principle of distinction. In this story the U.S. had discovered a chemical
weapons facility in the village, which American officials believed the Taliban was using to produce
weapons for use “against U.S. military forces and civilian personnel in Kabul, Afghanistan.” The
story reported that the Chairman of the Joint Chiefs of Staff had prepared a report to the President
describing two airstrike options for attacking the target. The first option, called the “small-scale
strike” would target three cruise missiles against the facility. The report estimated that the strike had
a 45 percent chance of destroying the target. Because the village was “densely populated” the strike
would also kill an estimated 20 Afghan civilians living in the village. The large scale strike would use
20 cruise missiles, doubling the chances of destroying the target to 90 percent, but increasing the
Afghan collateral civilian fatalities in the village to 500. The report stated that no U.S. military
deaths were expected in either operation.
17
For a critical review of these arguments see Toner 2005.
13
Each of the five experimental conditions then varied the information that subjects received
about the political attitudes or behavior of civilians in the village and whether or not the United
States was intentionally targeting the civilians.18 In condition A, subjects were told that although the
village was under Taliban control, “almost all of the residents of the village strongly oppose the
Taliban and the chemical facility.” Condition B specified that “almost all of the residents of the
village strongly support the Taliban and the chemical facility.” Both conditions clearly indicated,
however, that “the villagers have not fought for or provided food or weapons” to either the Taliban
or U.S.-allied forces. In other words, in both conditions the villagers met the definition of noncombatants under just war doctrine and international law since they did not make a direct or
significant contribution to the Taliban’s war effort.
Condition C parallels condition B, but adds that “many” villagers “voluntarily work in the
chemical facility” assisting the Taliban, thus raising the possibility that the villagers were making a
significant contribution to the Taliban’s war effort and might be liable to attack under just war
doctrine. Condition D also parallels condition B, but adds that the large-scale strike would be
“targeted against the chemical weapons lab as well as civilian houses in the surrounding village,”
which the report concludes would “send a strong message to Afghans in surrounding villages not to
support the Taliban.” Condition E parallels condition D, but adds that “many” villagers “voluntarily
provide food and shelter for Taliban fighters.” Note that the conditions in experiment 1 are not
fully crossed, so it is not possible to experimentally compare each condition to every other condition
in the experiment (e.g., it is not possible to compare condition A with condition E, or condition C
with condition D).
Experiment 2, which we refer to as the “due care experiment,” was devised to explore
Americans’ willingness to transfer risks from American soldiers onto foreign civilians. In this
experiment, subjects again read that the U.S. had discovered a Taliban chemical weapons laboratory
in an Afghan village. A report from the Chairman of the Joint Chiefs to the President described two
options for destroying the facility. In the first option, several thousand U.S. troops would “surround
the Taliban controlled town and deploy specially-trained Army Ranger units to locate and destroy
the chemical weapons components and laboratories.” The report noted that large numbers of
troops would need to search the village “house-to-house,” which would place them “at much greater
All three experiments employed experimental manipulations in several of the following locations in the story: the
headline, the head- lead, a pull quote, several sentences throughout the story, and in a table summarizing the
comparisons between the options being considered.
18
14
risk.” Because “American troops would only shoot when fired upon,” however, the door-to-door
operation would “avoid any Afghan civilian casualties.” In the second option described in the
report, the “troops would remain outside the town and use long-range artillery strikes to destroy
suspected Taliban buildings.”19 The report noted that the artillery strikes “would remove the risk to
U.S. military forces, but because the chemical weapons components and facilities are dispersed in a
residential area, Afghan civilian fatalities would be ‘dramatically higher’ compared to the house-tohouse option,” resulting in an estimated 200 civilian deaths.20 The report emphasized that “both
operations have a 90% chance of success.” The four experimental conditions then varied the
estimated number of U.S. military deaths in the house-to-house option from 5, to 50, to 200, to 250
while holding Afghan civilian casualties and all other features of the story constant.21
Experiment 3, which we have labeled the “proportionality/military advantage” experiment,
was designed to explore the trade-off between adversary civilian casualties and the military advantage
of destroying the target. In this experiment, subjects read that the United States had received
warning of a meeting of Taliban leaders in an Afghan village. As in experiment 1 (distinction),
subjects read that the Chairman of the Joint Chiefs of Staff had presented the President with the
choice between a large-scale strike and small-scale strike, both using unpiloted cruise missiles. The
small-scale strike had a 45% chance of destroying the target and was estimated to result in 20
Afghan collateral civilian deaths. The large-scale strike increased the chances of destroying the
target to 90% but also increased civilian casualties ten times to 200. In each scenario the story
emphasized that “the military will attempt to minimize Afghan civilian deaths,” but some deaths
were inevitable in either strike option because the village was densely populated.
The three conditions in experiment 3 vary the military advantage of destroying the target. In
condition A, subjects read that the strike would target “20 low-ranking Taliban officials” who
commanded a “local network of fighters” who carried out attacks in the area around the village.
The report from the Chairman of the Joint Chiefs of Staff concluded that eliminating the 20 leaders
would “contribute to the success of U.S. operations against the Taliban in the local area, but would
We chose an artillery strike instead of an airstrike to avoid varying the number of ground troops involved in the attack,
which could influence subjects’ approval of the two options.
20 The “house-to-house” and “artillery assault” scenarios were deigned to closely parallel the hypothetical “Close
Engagement” and “Distant Engagement” scenarios employed by David Luban (2014) to illustrate arguments about risktransfer and proportionality.
21 A 5th condition, not described here presented subjects with a range of U.S. fatalities from 0 to 10, which might be a
more realistic representation of the way people would receive estimates of fatalities in military operations. The results of
this condition were not significantly different from the condition with 5 U.S. military fatalities, however.
19
15
have little effect on the outcome of the war.” In condition B, the target was “20 high-ranking
Taliban officials” in charge of a “national network” carrying out national attacks. Eliminating the
high-ranking leasers was expected to “contribute to the success of U.S. operations against the
Taliban nationwide and would have a major effect on the outcome of the war.” Condition C
replicates condition B, adding the group was “planning attacks against the U.S. homeland” and that
eliminating them would also “greatly reduce the group’s ability to launch attacks against U.S.
targets.”
Immediately after reading the news stories, subjects were prompted to respond to a series of
approximately 50 survey questions. The first set of questions included manipulation checks and
focused on the subjects’ immediate reactions to the news story – including their preferences for
different attack options and their views of the ethicality of each option. Subjects then proceeded to
answer some more general questions regarding their attitudes towards the use of force and civilian
casualties in war.
Results
The findings reported in figure 1 show the results of experiment 1, which focused on attitudes
regarding the principle of distinction. The figure shows subjects’ responses to two key questions,
disaggregated across the five conditions. Subjects were asked: (1) “If you had to choose between the
two U.S. military options described in the article, would you prefer the small-scale or the large-scale
airstrike?” and (2) “Regardless of which option you preferred, how ethical or unethical do you think
it would be if the United States decided to launch the large-scale airstrike in this situation?”22
Figure 1: Distinction
Most questions in our survey utilized used a 6-point response scale (ranging from strongly agree/approve/prefer, to
strongly disagree/disapprove/do not prefer). In this paper we present dichotomized results for ease of interpretation.
There were no substantive differences in our results using the full 6 point response scale.
22
16
The results show that subjects were significantly more likely to prefer launching the largescale strike (killing 500 Afghan civilians instead of 20) when the civilians were described as political
supporters of the Taliban (thus failing to support hypothesis 3). 65 percent of subjects preferred the
large-scale strike when the victims were Taliban supporters (condition B), compared to 50 percent
who preferred it when the victims were Taliban opponents (condition A).23 Interestingly, although a
somewhat greater percentage of subjects (53% vs. 48%) were willing to describe the large-scale strike
as ethical when the civilian deaths would fall among Taliban supporters, the difference was much
smaller than the differences in preferences for the attack and not statistically significant. This might
suggest that Americans may have internalized the ethical principles of distinction, but not strongly
enough to alter their preferences in decisions about the use of force when faced with a real world
dilemma like the one we asked them to consider. Indeed, 52% of subjects across all the conditions
in experiment 1 agreed that “The United States must protect its most vital national interests even if
that sometimes requires doing things that are morally wrong.”24
Although the civilian fatalities in both conditions were described as collateral effects of the attack on the military target
(and thus do not fall strictly under the concept of distinction), these preferences run contrary to traditional
understandings of just war theory, which hold that the mere political affiliation of noncombatants is not morally relevant
in targeting decisions.
24 48 percent of subjects agreed with this statement when the civilian villagers were described as Taliban supporters
(condition B) compared to 59 percent who agreed when the victims were described as opponents (condition A). This
difference, however, was only marginally significant at p= .08.
23
17
The results also indicate that the degree of direct civilian involvement in the war effort has
surprisingly little effect on Americans’ willingness to inflict fatalities among foreign non-combatants
(failing to support hypothesis 2). Subjects were no more likely to prefer the large-scale strike when
civilian supporters in the village were described as voluntarily assisting the Taliban in making
chemical weapons (condition C) than when they were only political sympathizers (condition B).
However, subjects were significantly more likely to say the large-scale strike was ethical (53% to
63%) when the villagers were working in the Taliban facility. Again, this reinforces the conclusion
that the public’s ethical views and policy preferences about the use of force may sometimes diverge,
causing at least some Americans to support policies that they acknowledge may be ethically
questionable.
Finally, we did not find evidence to support that the majority of the public has internalized
the distinction principle’s clear prohibition on the intentional targeting of non-combatants (failing to
support hypothesis 1). Subjects were no less likely to prefer the large-scale strike when the strike
would target civilian supporters directly (conditions D and E), deliberately targeting civilian
dwellings in addition to the chemical facility to “send a strong signal” to other villages, than they
were when the civilian deaths were anticipated solely as the side effect of the attack on the chemical
weapons facility (condition B).25 Nearly two out of three Americans preferred the large-scale strike
even when it deliberately targeted civilians (condition D).26 Although it is possible that the
additional military benefit gained by “sending a message” to the Taliban could have offset subjects’
opposition to intentionally killing civilians in condition D, the fact that the subjects actually rated the
intentional attack as more ethical (62% in condition D compared to 53% in condition B) makes this
explanation implausible.27 In any case, since intentionally targeting civilians in wartime is frequently
undertaken in the effort to intimidate or coerce foreign civilians, our experimental comparison also
represents the choices military and political leaders face in the real world.
Interestingly, we also found no significant difference in subjects’ preference for or ethical
judgments of the large-scale strike when the civilians who would be intentionally targeted were
described as simply political supporters of the Taliban (condition D) or when the civilians actively
assisted the Taliban by providing them with food and shelter (condition E). For many Americans, in
Although the large-scale strike would also destroy the chemical weapons facility in conditions D and E, recall that the
doctrine of double effect prohibits attacks in which killing civilians in among any of the intended benefits of the attack.
26 The percentage rises to nearly 70% in the intentional targeting conditions when subjects were asked whether they
would “approve” of the strike, regardless of which option they preferred.
27 This difference was not significant, however (p=.12).
25
18
other words, civilians who provide political support for the adversary are judged to be just as liable
to attack as those directly contributing to the adversary’s war effort. Indeed, at least some subjects
appeared to reason that political supporters of the adversary are not “civilians” at all. Only 58
percent of subjects who read that the Afghan villagers were political supporters of the Taliban
(condition B) agreed that these villagers should be “considered civilians,” compared to 88 percent
who agreed when the villagers were described as opponents of the Taliban (condition A).28 In
condition C, where villagers were described as actively assisting the Taliban to build chemical
weapons, the proportion of subjects agreeing that the villagers should be considered civilians only
dropped by 5%, a level statistically indistinguishable from condition B.
We do not have clear hypotheses about whether individual-level traits influence the degree
to which subjects’ preferences accord with just war doctrine. Nevertheless, our research design
allows us to explore whether specific subgroups of the American public reacted differently to our
experimental stimuli. To examine this, we estimated a logistic regression equation with the subject’s
preference for the large-scale attack as the dependent variable and separate interactions between the
treatment condition and measures of the subject’s political party affiliation (republican or democrat),
current or prior military service, gender, age and college education as the independent variables.29
We also included an interaction between a dummy variable for Catholicism and the treatment
condition to explore whether Catholics, who might be more familiar with just war principles, would
respond differently to our stimuli. Overall, we found few significant interactions. In experiment 1,
only military service had a significant interactive effect on subjects’ preferences – substantially
increasing the preference for the large scale strike when the villagers were described as opponents of
the Taliban (condition A).30
We found somewhat stronger evidence that Americans beliefs about the use of force were
consistent with the logic of due care. Figure 2 shows the results of experiment 2, which focused on
Americans’ willingness to protect foreign civilians at the cost of risking the lives of American
soldiers. As in experiment 1, subjects were asked about their preference between two military
options – in this case, an artillery strike, which would kill 200 Afghan civilians, and a house-to-house
That difference is statistically significant at p < .001. The full wording of the question is: “In your opinion, should the
Afghan villagers described in the article be considered civilians or not?”
29 Due to space constraints this model is not reported. All the independent variables were dummy measures, with the
exception of age, which was continuous.
30 70% of subjects with current or prior military service preferred the large scale strike in condition A, compared with
47% of subjects with no military service.
28
19
assault, which would kill only 20. They were also asked whether they agreed that the artillery strike
was ethical. We found that significantly more subjects (74% vs. 49%) preferred the artillery strike
when doing so would avert the deaths of 50 American troops in the door-to-door operation
(condition B) than when it would avert only 5 U.S. military deaths (condition A). Subjects were also
much more likely (67% vs. 39%) to say the artillery strike was ethical when the door-to-door assault
was expected to result in 50 American military deaths than when 5 U.S. military deaths were
expected. These findings support hypotheses 5 and 6.
Figure 2: Due Care
Although these results suggest that most Americans recognize that American soldiers should
accept at least some risk in order to protect foreign civilians, they also suggest that Americans’ “risk
20
transfer ratio” is much higher than many proponents of just war theory would likely endorse. Even
when the artillery strike would avert the deaths 5 American soldiers at the cost of 200 Afghan
civilian deaths (condition A), a ratio of 40:1, only a bare majority (50.5%) preferred the more
discriminating door-to-door assault. When the artillery strike would allow the United States to avoid
50 military deaths, however, the preference for the artillery strike increased to nearly three-quarters
of the population. Interestingly, although support for the artillery strike remained high when the
expected American losses in the door-to-door operation increased to 200 (condition C) or 250
(condition D) fatalities, it did not significantly increase compared to condition B. This suggests that,
among those who were influenced by due care concerns at all, the risk transfer ratio must be greater
than 4:1 and for nearly half of all Americans, the ratio must be greater than 40:1 (200 civilian deaths
to avert 5 American military deaths).
Using the same technique and measures described above for experiment 1, we examined
whether age, party-ID, military service, gender, education and Catholicism significantly influenced
subjects’ responses to our stimuli. In experiment 2, only gender had a significant interaction with
the treatment – with men’s preference for the artillery strike rising much more quickly between
condition A and B than women’s.
These results are especially compelling because, in contrast to some conditions in
experiment 1, subjects in experiment 2 were not told that the Afghan civilians who would be killed
were supporters of the Taliban. Indeed, as we noted above, unlike many traditional interstate
conflicts, in which foreign civilians can be assumed to be supporters of the adversary, in Afghanistan
many civilians support the United States. Most of our subjects seemed to recognize this. 68 percent
of subjects in experiment 2 agreed that the Taliban villagers described in the article were either
opponents of the Taliban or neutral. In light of the results from experiment 1, therefore, it seems
probable that Americans might prefer even higher risk transfer ratios in military operations in which
the potential civilian victims are perceived as politically sympathetic to the adversary.
In experiment 3, we found evidence that American attitudes are generally consistent with the
moral logic of proportionality. This experiment focused on how the public’s willingness to accept
collateral civilian fatalities varied with the military advantage expected to be gained by destroying the
target (in this case, a meeting of Taliban leaders). The main results from this experiment are
reported in figure 3. As in experiment 1, subjects were asked whether they preferred a large-scale
missile strike, which offered a higher chance of success (90%) but would result in 200 collateral
21
Afghan civilian deaths or a small-scale strike, which would kill fewer civilians (20 deaths) but offered
only a 45% chance of success.
Figure 3: Proportionality - Military Advantage
The results indicate that Americans do appear to weigh foreign civilian deaths against the
military importance of the target (providing support for hypothesis 4). While 68% of Americans
preferred the large-scale strike on the meeting of high-ranking Taliban leaders (condition B), only
44% preferred it when the leaders were described as low ranking (condition A). Indeed, when asked
whether they would have approved “if the United States had decided not to strike the Taliban
meeting at all,” 54 percent of subjects in the low-level condition agreed, compared to 35 percent of
those in the high-level condition.31 Interestingly, subjects were no more likely to prefer the largescale strike in condition C, in which subjects read that the high-level Taliban leaders were also
planning attacks against the U.S. homeland. This suggests that among subjects whose support for
the large-scale strike was influenced by the military importance of the target at all, the chance to
eliminate 20 high levels leaders was sufficient reason to prefer the large-scale strike.
In this experiment, military service was, again, the only individual-level trait for which we
found a significant interaction with the stimuli. Subjects with military service were almost twice as
likely to prefer the large-scale attack against the “low level” meeting in condition A as the rest of the
population (70% vs. 39%), causing their preference for the large-scale attack to rise less sharply
between conditions A and B.
31
That difference is significant at p<.01
22
As in experiment 2, however, it is worth emphasizing that although Americans appear to
have followed the logic of proportionality, a very significant minority (44%) was nevertheless willing
to accept the deaths of 180 additional Afghan civilians in order to increase the chances of
eliminating a threat that American military leaders explicitly stated “would have little effect on the
outcome of the war.” Again, this suggests that although most Americans accept the basic moral
intuitions that undergird the principle of proportionality, the public’s commitment to the principle is
relatively shallow and easily outweighed by the desire to advance even secondary American national
security interests.
Discussion
These empirical findings point to three broad conclusions about the degree to which the American
public’s policy preferences regarding the use of military force are consistent with the jus in bello
principles of just war theory. First, at a most basic level, the public does appear to recognize and
accept the moral logic of the principles of due care and proportionality. They are willing to sacrifice
at least some American soldiers to spare the lives of larger numbers of foreign civilians. They are
less willing to tolerate civilian collateral civilian fatalities and are more willing to accept a lower
chance of success in military operations when destroying the target of the operation would achieve
relatively less military advantage. These findings suggest that considerations of proportionality and
due care are present in most Americans’ moral intuitions and can shape their policy preferences
about the use of force. Whether just war theory has evolved to reflect our preexisting intuitions on
these questions or whether hundreds of years of western legal, ethical and religious tradition have
shaped our moral views is not possible to discern from this study.
Second, however, the public’s commitment to these principles seems relatively fragile and
grants a degree of preference to American lives and national security interests far above what most
proponents of just war doctrine would likely endorse. To avert the death of 5 American soldiers,
nearly half of the American public (49.5%) would be willing to tolerate the collateral deaths of at
least 200 foreign civilians. Large minorities of the public are willing to accept hundreds of foreign
civilian deaths to increase the chances of success of strikes that even American military commanders
acknowledge will provide relatively little military advantage.
These findings strongly suggest that Americans have not internalized the most
“cosmopolitan” versions of just war theory. Rather, their views are closer to those of scholars like
Kasher and Yadlin (2005, 18) who argue that “a combatant is a citizen in uniform… His blood is as
23
red and thick as that of citizens who are not in uniform. His life is as precious as the life of anyone
else.” Under this view, the state’s primary interest during combat is in protecting the lives of its own
citizens and only secondary consideration is owed to the adversary’s civilians whose protection is the
responsibility of the adversary. Pooling across all the subjects in the three experiments described
above, 60% agreed that “protecting the lives of U.S. soldiers” ought to be “more important” than
“protecting the lives of foreign civilians” in times of war. Only 7% percent thought that the lives of
foreign civilians ought to be more important (33% said they should be equally important).
Third, our results provide much less evidence that public views on the use of force are
consistent with the principle of distinction, perhaps the most fundamental concept of jus in bello. A
large proportion of the public supports the intentional targeting of foreign civilians “to send a
message” to other civilians not to support the adversary – the kind of “terror bombing” explicitly
rejected by most just war proponents and strictly prohibited by international law. Americans are
also more willing to accept collateral foreign civilian deaths in U.S. military operations when the
civilian victims were viewed as politically sympathetic with the adversary (although few seem to
believe that killing political supporters is more morally justified than killing opponents). Many
Americans appear to deem that being a political supporter of the adversary is sufficient to cause
individuals to lose their status as “civilians” along with the protections that come with that status.
Conclusions
Some readers may be tempted to conclude from these findings that Americans lack strong
ethical principles when it comes to war and that the public simply favors any action that seems to
benefit the United States. In contrast, we believe the U.S. public’s moral intuitions seem to follow
an alternative “revisionist” view of the ethics of war, one supported by a small, but growing number
of revisionist scholars. This perspective rejects just war theory’s clear moral distinction between
soldiers and non-combatants in favor of a view that depends on judgments of moral responsibility
and liability to attack. In this understanding, noncombatants are not always morally innocent and
soldiers are not always legitimate targets in times of war.32 As a result, according to these
revisionists, traditional just war considerations of distinction, proportionality and due care must be
amended. Under certain conditions, revisionists argue, it may be ethically permissible to target
32
We examine the moral equivalence of soldiers in a separate experiment.
24
civilians directly if they are morally responsible for unjust wars or to trade the lives of culpable
civilians to protect the lives of morally innocent soldiers.
As Jeff McMahan (2009, 218), perhaps the most prominent just war revisionist scholar
writes, “there are ways in which civilians can be accessories to the fighting of an unjust war, and in
that way share responsibility for the war. Responsible civilians are therefore potentially liable to
certain forms of action that might be necessary to prevent or correct the wrongs involved in the
war.” McMahan argues that civilians can become liable not only by working directly for the war
effort (e.g., building weapons) but also if they help to “arouse support for the war” or possibly even
if they simply fail to take reasonable measures to protest the war. McMahan is careful to clarify that
not all such actions should increase civilians’ liability to be killed, but he does suggest that there may
be circumstances in which even the intentional targeting of civilians might be morally justified
(McMahan 2009, 221-224). Helen Frowe (2014, 187), another revisionist scholar, argues even more
directly that “we ought to reject the idea that the Principle of Non-Combatant Immunity picks out
any morally significant feature of non-combatants, and with it the idea that it is always morally
impermissible for just combatants to attack non-combatants on the unjust side of the war.”
These kinds of arguments are reflected in the attitudes and choices of the American public in
our experiments. In experiment 1, for example, 60% of subjects agreed that the “Afghan civilians in
this village must bear some responsibility for the civilian fatalities caused by the U.S. strike described
in the news story” when the villagers were described as political supporters of the Taliban (condition
B), compared to less than 20 percent when the villagers were described as opponents of the Taliban
(condition A).33 In fact, as noted above, in that experiment 42 percent of Americans asserted that
political supporters of the Taliban should not be considered civilians at all.
It is well beyond the scope of this paper to attempt to resolve the complex philosophical
debate between just war traditionalists and revisionists. Our results do have important implications,
however, regarding the practical application of ethical principles on the use of force. As noted
above, traditional just war theory is not simply a moral philosophy, but has long served as a practical
guide for the conduct of war, shaping international laws and national military doctrines on the use of
force. In this sense, traditional just war theory is not intended to codify our existing moral intuitions
about the use of force, but serves as a check on those intuitions when, in the strange and terrifying
33
This difference is significant at P<.001.
25
circumstances of war, they might lead us to justify terrible acts. Our results reinforce the urgent
need to maintain such a check.
As most revisionist scholars seem to recognize, their arguments on the “deep ethics” of war
are not a feasible guide for the practice of war. McMahan, for example, acknowledges that his
contention that it may be morally permissible to target civilians intentionally is “of limited practical
significance,” because the conditions that would need to be satisfied to justify the intentional
targeting of civilians “are impossible to satisfy in virtually all actual cases of military attacks against
civilians” (McMahan 2009, 224-225). In most cases, he argues, few civilians make a contribution to
the war significant enough to justify killing them and even if they did, killing some culpable civilians
would usually involve killing many innocent ones who just happen to live nearby. The results of our
study suggest that Americans appear to accept the revisionists’ argument that “responsible” civilians
may be liable to attack, but not the revisionists’ qualifications that usually render such attacks
impermissible in practice.
Nuanced judgments about moral culpability and innocence are difficult enough to render in
a philosopher’s thought experiments, but almost impossible to make consistently and objectively
given the complexity of the real world and the exigencies of war. With no impartial, international
judicial body capable of enforcing judgments on parties who make competing moral claims, it seems
likely that we will much too often choose to judge ourselves and our countrymen innocent and our
adversaries culpable. As McMahan (2009, 109) concludes, a rule that “permitted all combatants to
attack civilians in certain specified conditions… would be exploited by the unjust and inevitably
abused by the just, leading to greater violence” than a rule that simply banned such attacks
categorically. We find this concern amply validated in our results.
Indeed, the same logic that subjects in our experiment seem to have employed to justify
attacks on civilian political supporters of the Taliban has been employed by enemies of the United
States to justify attacks on American civilians. This mode of reasoning was explicit, for example, in
Osama Bin Laden’s 2002 “Letter to America,” in which he articulated his justification for the attacks
of September 11, 2001. After claiming that Al Qaeda’s attacks were warranted in response to
numerous alleged acts of aggression that the United States had committed against Muslims around
the world, Bin Laden attempted to preempt his critics, writing,
You may then dispute that all the above does not justify aggression against
[American] civilians, for crimes they did not commit and offenses in which they did
not partake… This argument contradicts your continuous repetition that America is
26
the land of freedom... Therefore, the American people are the ones who choose their
government by way of their own free will; a choice which stems from their
agreement to its policies… The American people have the ability and choice to
refuse the policies of their Government and even to change it if they want. The
American people are the ones who pay the taxes… So the American people are the
ones who fund the attacks against us, and they are the ones who oversee the
expenditure of these monies in the way they wish, through their elected candidates…
This is why the American people cannot be innocent of all the crimes committed…
against us (quoted in Guardian 2002).
As a result of concerns about enabling arguments such as this, McMahan (2009, 109)
concedes that, as a matter of practice, the laws of war and the ethics of war should remain separate
and he accepts that current just war guidelines provide a reasonably sound basis for such laws. Our
results suggest, however, that the American public does not appear to recognize this subtle but
critical distinction between revisionist ethics and practice. Many Americans are willing to substitute
just war doctrine’s bright line between soldiers and civilians in favor of relatively crude views of
moral culpability. Both traditional just war theorists and revisionists, therefore, should consider
these findings disturbing and regrettable.
27
Table 1: Summary of Experimental Conditions
EXPERIMENT 1
DISTINCTION/CULPABILITY
TARGET
SCENARIO
DESCRIPTION
Taliban chemical weapons lab
U.S. must choose between a largescale or small-scale airstrike. The
large-scale strike kills more Afghan
civilians than the small scale strike
(500 vs. 20) but is more likely to
destroy target (90% vs. 45% chance
of success). Conditions vary the
“culpability” of Afghan civilians.
CONDITION A
villagers politically oppose Taliban
CONDITION B
villagers politically support Taliban
CONDITION C
and work in weapons factory
CONDITION D
and the U.S. intentionally targets
civilians.
CONDITION E
and provide food to the Taliban and
the U.S. intentionally targets
civilians.
EXPERIMENT 2
DUE CARE
EXPERIMENT 3
PROPORTIONALITY
Taliban chemical weapons lab
U.S. must choose between a
house-to-house assault or an
artillery strike. The house-tohouse assault will result in more
U.S. military deaths, but fewer
Afghan civilian deaths.
Conditions vary ratio of U.S.
military deaths to Afghan civilian
deaths.
House-to-house fatalities:
5 US mil. / 0 Afghan civ.
Artillery fatalities:
0 U.S. mil/ 200 Afghan civ.
Meeting of Taliban leaders
U.S. must choose between a largescale or small-scale airstrike. The
large-scale strike kills more
Afghan civilians than the smallscale strike (200 vs. 20) but is
more likely to destroy target (45%
vs. 90%). Conditions vary
importance of Taliban leaders.
50 US mil. / 0 Afghan civ.
0 U.S. mil. / 200 Afghan civ.
200 US mil. /0 Afghan civ.
0 U.S. mil. / 200 Afghan civ.
high level, national
Taliban leaders
250 US mil. /0 Afghan civ
0 U.S. mil./ 200 Afghan civ.
28
low level, local
Taliban leaders
high level, national Taliban
leaders planning attacks on U.S.
homeland
Appendix: Experimental Treatments
EXPERIMENT 1/CONDITION A
29
EXPERIMENT 1/CONDITION B
30
EXPERIMENT 1/CONDITION C
31
EXPERIMENT 1/CONDITION D
32
EXPERIMENT 1/CONDITION E
33
34
35
36
EXPERIMENT 2/CONDITION D
37
38
39
40
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Scott D. Sagan, Stanford University Benjamin A. Valentino

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