## 1. Traditionalists and Revisionists



Contemporary just war theory is dominated by two camps: traditionalist
and
 revisionist.[3]
 The traditionalists might as readily be called legalists. Their views
on the morality of war are substantially led by international law,
especially the law of armed conflict. They aim to provide those laws
with morally defensible foundations. States (and only states) are
permitted to go to war only for national defence, defence of other
states, or to intervene to avert "crimes that shock the moral
conscience of mankind" (Walzer 2006: 107). Civilians may not be
targeted in war, but all combatants, whatever they are fighting for,
are morally permitted to target one another, even when doing so
foreseeably harms some civilians (so long as it does not do so
 excessively).[4]



Revisionists question the moral standing of states and the
permissibility of national defence, argue for expanded permissions for
humanitarian intervention, problematise civilian immunity, and contend
that combatants fighting for wrongful aims cannot do anything right,
besides lay down their weapons.



Most revisionists are *moral* revisionists only: they deny that
the contemporary law of armed conflict is intrinsically morally
justified, but believe, mostly for pragmatic reasons, that it need not
be substantially changed. Some, however, are both morally and legally
revisionist. And even moral revisionists' disagreement with the
traditionalists is hardly ersatz: most believe that, faced with a
clash between what is morally and what is legally permitted or
prohibited, individuals should follow their conscience rather than the
 law.[5]



The traditionalist view received its most prominent exposition the
same year as it was decisively codified in international law, in the
first additional protocol to the Geneva Conventions. Michael
Walzer's *Just and Unjust Wars*, first published in 1977,
has been extraordinarily influential among philosophers, political
scientists, international lawyers, and military practitioners. Among
its key contributions were its defence of central traditionalist
positions on national defence, humanitarian intervention,
discrimination, and combatant equality.



Early revisionists challenged Walzer's views on national defence
(Luban 1980a) and humanitarian intervention (Luban 1980b). Revisionist
criticism of combatant equality and discrimination followed (Holmes
1989; McMahan 1994; Norman 1995). Since then there has been an
explosion of revisionist rebuttals of Walzer (for example Rodin 2002;
McMahan 2004b; McPherson 2004; Arneson 2006; Fabre 2009; McMahan 2009;
Fabre 2012).



Concurrently, many philosophers welcomed Walzer's conclusions,
but rejected his arguments. They have accordingly sought firmer
foundations for broadly traditionalist positions on national defence
(Benbaji 2014; Moore 2014), humanitarian intervention (Coady 2002),
discrimination (Rodin 2008b; Dill and Shue 2012; Lazar 2015c), and
especially combatant equality (Zohar 1993; Kutz 2005; Benbaji 2008;
Shue 2008; Steinhoff 2008; Emerton and Handfield 2009; Benbaji
2011).



We will delve deeper into these debates in what follows. First,
though, some methodological groundwork. Traditionalists and
revisionists alike often rely on methodological or second-order
premises, to the extent that one might think that the first-order
questions are really just proxy battles through which they work out
their deeper disagreements (Lazar and Valentini forthcoming).


## 2. How Should We Think about the Morality of War?


### 2.1 Historical vs Contemporary Just War Theory



For the sake of concision this entry discusses only contemporary analytical
philosophers working on war. Readers are directed to the excellent work
of philosophers and intellectual historians such as Greg Reichberg,
Pablo Kalmanovitz, Daniel Schwartz, and Rory Cox to gain further
insights about historical just war theory (see, in particular, Cox
2016; Kalmanovitz 2016; Reichberg 2016; Schwartz 2016).


### 2.2 Institutions and Actions



Within contemporary analytical philosophy, there are two different
ways in which moral and political philosophers think about war (Lazar
and Valentini forthcoming). On the first, *institutionalist*,
approach, philosophers' primary goal is to establish what the
institutions regulating war should be. In particular, we should
prescribe morally justified laws of war. We then tell individuals and
groups that they ought to follow those laws. On the second approach,
we should focus first on the moral reasons that apply directly to
individual and group actions, without the mediating factor of
institutions. We tell individuals and groups to act as their moral
reasons dictate. Since this approach focuses not on the institutions
that govern our interactions, but on those interactions themselves, we
will call it the "interactional"
 approach.[6]



In general, the institutionalist approach is favoured by indirect
consequentialists and contractualists. Indirect consequentialists
believe these institutions are justified just in case they will in
fact have better long-run results than any feasible alternative
institutions (see Mavrodes 1975; Dill and Shue 2012; Shue 2013;
Waldron 2016). Contractualists believe these institutions ground or
reflect either an actual or a hypothetical contract among states
and/or their citizens, which specifies the terms of their interaction
in war (see Benbaji 2008, 2011, 2014; Statman 2014).



Non-contractualist deontologists and direct- or act-consequentialists
tend to prefer the interactional approach. Their central question is:
what moral reasons bear directly on the permissibility of killing in
war? This focus on killing might seem myopic--war involves much
more violence and destruction than the killing alone. However,
typically this is just a heuristic device; since we typically think of
killing as the most presumptively wrongful kind of harm, whatever
arguments one identifies that justify killing are likely also to
justify lesser wrongs. And if the killing that war involves cannot be
justified, then we should endorse pacifism.



Any normative theory of war should pay attention both to what the laws
of war should be, and to what we morally ought to do. These are two
distinct but equally important questions. And they entail the
importance of a third: what ought we to do all things considered, for
example when law and morality conflict? Too much recent just war
theory has focused on arguing that philosophical attention should be
reserved to one of the first two of these questions (Buchanan 2006;
Shue 2008, 2010; Rodin 2011b). Not enough has concentrated on the
third (though see McMahan 2008; Lazar 2012a).



Although this entry touches on the first question, it focuses on the
second. Addressing the first requires detailed empirical research and
pragmatic political speculation, both of which are beyond my remit
here. Addressing the third takes us too deep into the minutiae of
contemporary just war theory for an encyclopaedia entry.



What's more, even institutionalists need some answer to the
second question--and so some account of the interactional
morality of war. Rule-consequentialists need an account of the good
(bad) that they are hoping that the ideal laws of war will maximise
(minimise) in the long run. This means, for example, deciding whether
to aim to minimise all harm, or only to minimise wrongful harm. The
latter course is much more plausible--we wouldn't want laws
of war that, for example, licensed genocide just in case doing so
leads to fewer deaths overall. But to follow this course, we need to
know which harms are (extra-institutionally) wrongful. Similarly,
contractualists typically acknowledge various constraints on the kinds
of rules that could form the basis of a legitimate contract, which,
again, we cannot work out without thinking about the
extra-institutional morality of war (Benbaji 2011).


### 2.3 Overarching Disputes in Contemporary Analytical Just War Theory



Even within interactional just war theory, several second-order
disagreements underscore first-order disputes. First: when thinking
about the ethics of war, what kinds of cases should we use to test our
intuitions and our principles? We can start by thinking about actual
wars and realistic wartime scenarios, paying attention to
international affairs and military history. Or, more clinically, we
can construct hypothetical cases to isolate variables and test their
impact on our intuitions.



Some early revisionists relied heavily on highly artificial cases
(e.g., McMahan 1994; Rodin 2002). They were criticized for this by
traditionalists, who generally use more empirically-informed examples
(Walzer 2006). But one's standpoint on the substantive questions
at issue between traditionalists and revisionists need not be
predetermined by one's methodology. Revisionists can pay close
attention to actual conflicts (e.g., Fabre 2012). Traditionalists can
use artificial hypotheticals (e.g., Emerton and Handfield 2009; Lazar
2013).



Abstraction forestalls unhelpful disputes over historical details. It
also reduces bias--we are inclined to view actual conflicts
through the lens of our own political allegiances. But it also has
costs. We should be proportionately less confident of our intuitions
the more removed the test case is from our lived experience.
Philosophers' scenarios involving mind-control, armed
pedestrians, trolleys, meteorites, and incredibly complicated causal
sequences are pure exercises in imagination. How can we trust our
judgements about such cases more than we trust our views on actual,
realistic scenarios? What's more, abandoning the harrowing
experience of war for sanitized hypothetical cases might be not merely
epistemically unsound, but also disrespectful of the victims of war.
Lastly, cleaned-up examples often omit morally relevant
details--for instance, assuming that everyone has all the
information relevant to their choice, rather than acknowledging the
"fog of war", and making no allowances for fear or
trauma.



Artificial hypotheticals have their place, but any conclusions they
support must be tested against the messy reality of war. What's
more, our intuitive judgements should be the starting-point for
investigation, rather than its end.



The second divide is related to the first. *Reductivists* think
that killing in war must be justified by the same properties that
justify killing outside of war. *Non-reductivists*, sometimes
called *exceptionalists*, think that some properties justify
killing in war that do not justify killing outside of
 war.[7]
 Most exceptionalists think that specific features of killing in war
make it morally different from killing in ordinary life--for
example, the scale of the conflict, widespread and egregious
non-compliance with fundamental moral norms, the political interests
at stake, the acute uncertainty, the existence of the law of armed
conflict, or the fact that the parties to the conflict are organized
groups. A paradigm reductivist, by contrast, might argue
that justified wars are mere aggregates of justified acts of
individual self- and other-defence (see Rodin 2002; McMahan 2004a).



Reductivists are much more likely to use far-fetched hypothetical
cases, since they think there is nothing special about warfare. The
opposite is true for exceptionalists. Walzer's first critics
relied on reductivist premises to undermine the principles of national
defence (Luban 1980a; Rodin 2002), discrimination (Holmes 1989;
McMahan 1994), and combatant equality (Holmes 1989; McMahan 1994).
Many traditionalists replied by rejecting reductivism, arguing that
there is something special about war that justifies a divergence from
the kinds of judgements that are appropriate to other kinds of
conflict (Zohar 1993; Kutz 2005; Benbaji 2008; Dill and Shue 2012).
Again, some philosophers buck these overarching trends (for
reductivist traditionalist arguments, see e.g., Emerton and Handfield
2009; Lazar 2015c; Haque 2017; for non-reductivist revisionist
arguments, see e.g., Ryan 2016).



The debate between reductivism and exceptionalism is
overblown--the concept of "war" is vague, and while
typical wars involve properties that are not instantiated in typical
conflicts outside of war, we can always come up with far-fetched
hypotheticals that don't involve those properties, which we
wouldn't call "wars". But this masks a deeper
methodological disagreement: when thinking about the morality of war,
should we start by thinking about war, or by thinking about the
permissible use of force outside of war? Should we model justified
killing in war on justified killing outside of war? Or, in focusing on
the justification of killing in war, might we then discover that there
are some non-canonical cases of permissible killing outside of war? My
own view is that thinking about justified killing outside of war has
its place, but must be complemented by thinking about war
directly.



Next, we can distinguish between individualists and collectivists; and
we can subdivide them further into *evaluative* and
*descriptive* categories. Evaluative individualists think that
a collective's moral significance is wholly reducible to its
contribution to the well-being of the individuals who compose it.
Evaluative collectivists think that collectives can matter
independently of how they contribute to individual well-being.
Descriptive individualists think that any act that might appear to be
collective is reducible to component acts by individuals. Descriptive
collectivists deny this, thinking that some acts are irreducibly
 collective.[8]



Again, the dialectic of contemporary just war theory involves
revisionists first arguing that we cannot vindicate traditionalist
positions on descriptively and evaluatively individualist grounds,
with some traditionalists then responding by rejecting descriptive
(Kutz 2005; Walzer 2006; Lazar 2012b) and evaluative individualism
(Zohar 1993). And again there are outliers--individualist
traditionalists (e.g., Emerton and Handfield 2009) and collectivist
revisionists (e.g., Bazargan 2013).



Unlike the reductivist/exceptionalist divide, the
individualist/collectivist split cannot be resolved by thinking about
the morality of war on its own. War is a useful test case for theories
of collective action and the value of collectives, but no more than
that. Intuitions about war are no substitute for a theory of
collective action. Perhaps some collectives have value beyond their
contribution to the well-being of their members. For example, they
might instantiate justice, or solidarity, which can be impersonally
valuable (Temkin 1993). It is doubtful, however, that groups have
*interests* independent from the well-being of their members.
On the descriptive side, even if we can reduce collective actions to
the actions of individual members, this probably involves such
complicated contortions that we should seriously question whether it
is worth doing (Lazar 2012b).


### 2.4 Dividing up the Subject Matter



Traditionally, just war theorists divide their enquiry into reflection
on the resort to war--*jus ad bellum*--and conduct in
war--*jus in bello*. More recently, they have added an
account of permissible action post-war, or *jus post bellum*.
Others suggest an independent focus on war exit, which they have
variously called *jus ex bello* and *jus terminatio*
(Moellendorf 2008; Rodin 2008a). These Latin labels, though
unfortunately obscurantist, serve as a useful shorthand. When we refer
to *ad bellum* justice, we mean to evaluate the permissibility
of the war as a whole. This is particularly salient when deciding to
launch the war. But it is also crucial for the decision to continue
fighting. *Jus ex bello*, then, fits within *jus ad
bellum*. The *jus in bello* denotes the permissibility of
particular actions that compose the war, short of the war as a
whole.


### 2.5 The Decisive Role of Necessity and Proportionality



Traditional just war theory construes *jus ad bellum* and
*jus in bello* as sets of principles, satisfying which is
necessary and sufficient for a war's being permissible. *Jus
ad bellum* typically comprises the following six principles:


1. Just Cause: the war is an attempt to avert the right kind of
injury.
2. Legitimate Authority: the war is fought by an entity that has the
authority to fight such wars.
3. Right Intention: that entity intends to achieve the just cause,
rather than using it as an excuse to achieve some wrongful end.
4. Reasonable Prospects of Success: the war is sufficiently likely
to achieve its aims.
5. Proportionality: the morally weighted goods achieved by the war
outweigh the morally weighted bads that it will cause.
6. Last Resort (Necessity): there is no other less harmful way to
achieve the just cause.



Typically the *jus in bello* list comprises:


1. Discrimination: belligerents must always distinguish between
military objectives and civilians, and intentionally attack only
military objectives.
2. Proportionality: foreseen but unintended harms must be
proportionate to the military advantage achieved.
3. Necessity: the least harmful means feasible must be used.



These all matter to the ethics of war, and will be addressed below.
However, it is unhelpful to view them as a checklist of necessary and
sufficient conditions. When they are properly understood, only
proportionality and necessity (in the guise of last resort in the
*jus ad bellum*) are necessary conditions for a war, or an act
in a war, to be permissible, since no matter how badly going to war
fails the other *ad bellum* criteria (for example) it might
still be permissible because it is the least awful of one's
alternatives, and so satisfies the necessity and proportionality
constraints.



To get an intuitive grasp on necessity and proportionality, note that
if someone threatens my life, then killing her would be proportionate;
but if I could stop her by knocking her out, then killing her would be
unnecessary, and so impermissible. The necessity and proportionality
constraints have the same root: with few exceptions (perhaps when it
is deserved), harm is intrinsically bad. Harms (and indeed all bads)
that we cause must therefore be justified by some positive reason that
counts in their favour--such as good achieved or evil averted
(Lazar 2012a). Both the necessity and proportionality constraints
involve comparing the bads caused by an action with the goods that it
achieves. They differ only in the kinds of options they compare.



The use of force is proportionate when the harm done is
counterbalanced by the good achieved in averting a threat. To
determine this, we typically compare the candidate course of action
with what would happen if we allowed the threat to eventuate.



Of course, in most cases we will have more than one means of averting
or mitigating the threat. And a harmful option can be permissible only
if *all* the harm that it involves is justified by a
corresponding good achieved. If some alternative would as successfully
avert the threat, but cause less harm, then the more harmful option is
impermissible, because it involves unnecessary harm.



Where an option *O* aims to avert a threat *T*, we determine
*O*'s necessity by comparing it with all the other options
that will either mitigate or avert *T*. We determine its
proportionality by comparing it with the harm suffered if *T*
should come about. The only difference between the proportionality and
necessity constraints is that the former involves comparing
one's action with a very specific counterfactual
scenario--in which we don't act to avert the
threat--while the latter involves comparing it with all your
available options that have some prospect of averting or mitigating
the threat. In my view, we should simply expand this so that the
necessity constraint compares all your available options bar none.
Then proportionality would essentially involve comparing each option
with the alternative of doing nothing, while necessity would involve
comparing all options (including doing nothing) in terms of their
respective balances of goods and bads. On this approach, necessity
would subsume proportionality. But this is a technical point with
little substantive payoff.



More substantively, necessity and proportionality judgements concern
consequences, and yet they are typically made *ex ante*, before
we know what the results of our actions will be. They must therefore
be modified to take this uncertainty into account. The most obvious
solution is simply to refer to *expected* threats and
*expected* harms, where the expected harm of an option *O*
is the probability-weighted average of the harms that might result if
I take *O*, and the expected threat is the probability-weighted
average of the consequences of doing nothing to prevent the
threat--allowing for the possibility that the threat might not
eventuate at all (Lazar 2012b). We would also have to factor in the
options' probability of averting the threat. This simple move
obscures a number of important and undertheorised issues that we
cannot discuss in detail here. For now, we must simply note that
proportionality and necessity must be appropriately indexed to the
agent's uncertainty.



Necessity and proportionality judgements involve weighing harms
inflicted and threats averted, indeed all relevant goods and bads. The
simplest way to proceed would be to aggregate the harms to individual
people on each side, and call the act proportionate just in case it
averts more harm than it causes, and necessary just in case no
alternative involves less harm. But few deontologists, and indeed few
non-philosophers, think in this naively aggregative way. Instead we
should weight harms (etc.) according to factors such as whether the
agent is directly responsible for them, and whether they are intended
or merely
 foreseen.[9]
 Many also think that we can, perhaps even must, give greater
importance in our deliberations to our loved ones (for example) than
to those tied to us only by the common bonds of humanity (Hurka 2007;
Lazar 2013; for criticism, see Lefkowitz 2009). Similarly, we might justifiably
prioritise defending our own state's sovereignty and territorial
integrity, even when doing so would not be impartially
 best.[10]
 Only when all these and other factors (many of which are discussed
below) are taken into consideration can we form defensible conclusions
about which options are necessary and proportionate.



The other elements of the ethics of war contribute to the evaluation
of proportionality and necessity, in one (or more) of three ways:
identifying positive reasons in favour of fighting; delineating the
negative reasons against fighting; or as staging-posts on the way to
judgements of necessity and proportionality.



Given the gravity of the decision to go to war, only very serious
threats can give us just cause to fight. So if just cause is
satisfied, then you have weighty positive reasons to fight. Lacking
just cause does not *in itself* aggravate the badness of
fighting, but does make it less likely that the people killed in
pursuing one's war aims will be liable to be killed (more on
this below, and see McMahan 2005a), which makes killing very hard to
justify. Even if having a just cause is not strictly speaking a
necessary condition for warfare to be permissible, the absence of a
just cause makes it very difficult for a war to satisfy
proportionality.



If legitimate authority is satisfied then additional positive reasons
count in favour of fighting (see below). If it is not satisfied, then
this adds an additional reason against fighting, which must be
overcome for fighting to be proportionate.



The "reasonable prospects of success" criterion is a
surmountable hurdle on the way to proportionality. Typically, if a war
lacks reasonable prospects of success, then it will be
disproportionate, since wars always involve causing significant harms,
and if those harms are likely to be pointless then they are unlikely
to be justified. But of course sometimes one's likelihood of
victory is very low, and yet fighting is still the best available
option, and so necessary and proportionate. Having reasonable
prospects of success matters only for the same reasons that necessity
and proportionality matter. If necessity and proportionality are
satisfied, then the reasonable prospects of success standard is
irrelevant.



Right intention may also be irrelevant, but insofar as it matters its
absence would be a reason against fighting; having the right intention
does not give a positive reason to fight.



Lastly, discrimination is crucial to establishing proportionality and
necessity, because it tells us how to weigh the lives taken in
war.


## 3. *Jus ad Bellum*


### 3.1 Just Cause



Wars destroy lives and environments. In the eight years following the
Iraq invasion in 2003, half a million deaths were either directly or
indirectly caused by the war (Hagopian et al. 2013). Direct casualties
from the Second World War numbered over 60 million, about 3 per cent
of the world's population. War's environmental costs are
less commonly researched, but are obviously also extraordinary (Austin
and Bruch 2000). Armed forces use fuels in Olympian quantities: in the
years from 2000-2013, the US Department of Defense accounted for
around 80% of US federal government energy usage, between 0.75 and 1
quadrillion BTUs per year--a little less than *all* the
energy use that year in Denmark and Bulgaria, a little more than
Slovakia and Serbia (Energy Information Administration 2015a,b). They
also directly and indirectly destroy habitats and natural
resources--consider, for example, the Gulf war oil spill (El-Baz
and Makharita 1994). For both our planet and its inhabitants, wars are
truly among the very worst things we can do.



War can be necessary and proportionate only if it serves an end worth
all this death and destruction. Hence the importance of having a just
cause. And hence too the widespread belief that just causes are few
and far between. Indeed, traditional just war theory recognizes only
two kinds of justification for war: national defence (of one's
own state or of an ally) and humanitarian intervention. What's
more, humanitarian intervention is permissible only to avert the very
gravest of tragedies--"crimes that shock the moral
conscience of mankind" (Walzer 2006: 107).



Walzer argued that states' claims to sovereignty and territorial
integrity are grounded in the human rights of their citizens, in three
ways. First, states ensure individual security. Rights to life and
liberty have value "only if they also have dimension"
(Walzer 2006: 58), which they derive from states'
borders--"within that world, men and women... are safe
from attack; once the lines are crossed, safety is gone" (Walzer
2006: 57). Second, states protect a common life, made by their
citizens over centuries of interaction. If the common life of a
political community is valued by its citizens, then it is worth
fighting for. Third, they have also formed a political association, an
organic social contract, whereby individuals have, over time and in
informal ways, conceded aspects of their liberty to the community, to
secure greater freedom for all.



These arguments for national defence are double-edged. They helped
explain why wars of national defence are permissible, but also make
justifying humanitarian intervention harder. One can in principle
successfully conclude a war in defence of oneself or one's allies without any lasting
damage to the political sovereignty or territorial integrity of any of
the contending parties. In Walzer's view, humanitarian
interventions, in which one typically defends people against their own
state, necessarily undermine political sovereignty and territorial
integrity. So they must meet a higher burden of justification.



Walzer's traditionalist stances on national defence and
humanitarian intervention met heavy criticism. Early sceptics (Doppelt
1978; Beitz 1980; Luban 1980a) challenged Walzer's appeal to the
value of collective freedom, noting that in diverse political
communities freedom for the majority can mean oppression for the
minority (see also Caney 2006). In modern states, can we even speak of
a single common life? Even if we can, do wars really threaten it,
besides in extreme cases? And even if our common life and culture were
threatened, would their defence really justify killing innocent
people?



Critics also excoriated Walzer's appeal to individual rights
(see especially Wasserstrom 1978; Luban 1980b). They questioned the
normative purchase of his metaphor of the organic social contract (if
hypothetical contracts aren't worth the paper they're not
written on, then what are metaphorical contracts worth?). They
challenged his claim that states guarantee individual security: most
obviously, when humanitarian intervention seems warranted, the state
is typically the greatest threat to its members.



David Rodin (2002) advanced the quintessentially reductivist critique
of Walzer, showing that his attempt to ground state defence in
individual defensive rights could not succeed. He popularized the
"bloodless invasion objection" to this argument for
national defensive rights. Suppose an unjustly aggressing army would
secure its objectives without loss of life if only the victim state
offers no resistance (the 2001 invasion of Afghanistan, and the 2003
invasion of Iraq, arguably meet this description, as might some of
Russia's territorial expansions). If the right of national
defence is grounded in states' members' rights to
security, then in these cases there would be no right of national
defence, because their lives are at risk only if the victim state
fights back. And yet we typically do think it permissible to fight
against annexation and regime change.



By undermining the value of sovereignty, revisionists lowered the bar
against intervening militarily in other states. Often these arguments
were directly linked: some think that if states cannot protect the
security of their members, then they lack any rights to sovereignty
that a military intervention could undermine (Shue
 1997).[11]
 Caney (2005) argues that military intervention could be permissible
were it to serve individual human rights better than non-intervention.
Others countenance so-called "redistributive wars", fought
on behalf of the global poor to force rich states to address the
widespread violations of fundamental human rights caused by their
economic policies (Luban 1980b; Fabre 2012; Lippert-Rasmussen 2013;
Overland 2013).



Other philosophers, equally unpersuaded by Walzer's arguments,
nonetheless reject a substantively revisionist take on just cause. If
the individual self-defence-based view of *jus ad bellum*
cannot justify lethal defence against "lesser aggression",
then we *could* follow Rodin (2014), and argue for radically
revisionist conclusions about just cause; or we could instead reject
the individual self-defence-based approach to justifying killing in
war (Emerton and Handfield 2014; Lazar 2014).



Some think we can solve the "problem of lesser aggression"
by invoking the importance of deterrence, as well as the impossibility
of knowing for sure that aggression will be bloodless (Fabre 2014).
Others think that we must take proper account of people's
interest in having a democratically elected, or at least home-grown,
government, to justify national defence. On one popular account,
although no individual could permissibly kill to protect her own
"political interests", when enough people are threatened,
their aggregated interests justify going to war (Hurka 2007; Frowe
2014). Counterintuitively, this means that more populous states have,
other things equal, more expansive rights of national defence.
However, perhaps states have a group right to national defence, which
requires only that a sufficient number of individuals have the
relevant political interests--any excess over the threshold is
morally irrelevant. Many already think about national
self-determination in this way: the population of the group seeking
independence has to be sufficiently large before we take their claim
seriously, but differences above that threshold matter much less
(Margalit and Raz 1990).



The revisionist take on humanitarian intervention might also have some
troubling results. If sovereignty and territorial integrity matter
little, then shouldn't we use military force more often? As Kutz
(2014) has argued, revisionist views on national defence might license
the kind of military adventurism that went so badly wrong in Iraq,
where states have so little regard for sovereignty that they go to war
to improve the domestic political institutions of their
adversaries.



We can resolve this worry in one of two ways. First, recall just how
infrequently military intervention succeeds. Since it so often not
only fails, but actually makes things worse, we should use it only
when the ongoing crimes are so severe that we would take any risk to
try to stop them.



Second, perhaps the political interests underpinning the state's
right to national defence are not simply interests in being part of an
ideal liberal democracy, but in being governed by, very broadly,
members of one's own nation, or perhaps even an interest in
collective self-determination. This may take us back to Walzer's
"romance of the nation-state", but people clearly do care
about something like this. Unless we want to restrict rights of
national defence to liberal democracies alone (bearing in mind how few
of them there are in the world), we have to recognize that our
political interests are not all exclusively liberal-democratic.



What of redistributive wars? Too often arguments on this topic
artfully distinguish between just cause and other conditions of
*jus ad bellum* (Fabre 2012). Even when used by powerful states
against weak adversaries, military force is rarely a moral triumph. It
tends to cause more problems than it solves. Redistributive wars, as
fought on behalf of the "global poor" against the
"global rich", would obviously fail to achieve their
objectives, indeed they would radically exacerbate the suffering of
those they aim to help. So they would be disproportionate, and cannot
satisfy the necessity constraint. The theoretical point that, in
principle, not only national defence and humanitarian intervention
could give just causes for war is sound. But this example is in
practice irrelevant (for a robust critique of redistributive
wars, see Benbaji 2014).



And yet, given the likely path of climate change, the future might see
resource wars grow in salience. As powerful states find themselves
lacking crucial resources, held by other states, we might find that
military attack is the best available means to secure these resources,
and save lives. Perhaps in some such circumstances resource wars could
be a realistic option.


### 3.2 Just Peace



The goods and bads relevant to *ad bellum* proportionality and
necessity extend far beyond the armistice. This is obvious, but has
recently received much-needed emphasis, both among philosophers and in
the broader public debate sparked by the conflicts in Iraq and
Afghanistan (Bass 2004; Coady 2008; May 2012). Achieving your just
cause is not enough. The aftermath of the war must also be
sufficiently tolerable if the war is to be proportionate, all things
considered. It is an open question how far into the future we have to
look to assess the morally relevant consequences of conflict.


### 3.3 Legitimate Authority



Historically, just war theory has been dominated by statists. Most
branches of the tradition have had some version of a
"legitimate", "proper" or "right"
authority constraint, construed as a necessary condition for a war to
be *ad bellum*
 just.[12]
 In practice, this means that sovereigns and states have rights that
non-state actors lack. International law gives only states rights of
national defence and bestows "combatant rights" primarily
on the soldiers of states. Although Walzer said little about
legitimate authority, his arguments all assume that states have a
special moral standing that non-state actors lack.



The traditionalist, then, says it matters that the body fighting the
war have the appropriate authority to do so. Some think that authority
is grounded in the overall legitimacy of the state. Others think that
overall legitimacy is irrelevant--what matters is whether the
body fighting the war is authorized to do so by the polity that it
represents (Lazar forthcoming-b). Either way, states are much more
likely to satisfy the legitimate authority condition than non-state
actors.



Revisionists push back: relying on reductivist premises, they argue
that killing in war is justified by the protection of individual
rights, and our licence to defend our rights need not be mediated
through state institutions. Either we should disregard the legitimate
authority condition or we should see it as something that non-state
actors can, in fact, fulfil (Fabre 2008; Finlay 2010; Schwenkenbecher
2013).



Overall, state legitimacy definitely seems relevant for some questions
in war (Estlund 2007; Renzo 2013). But authorization is more
fundamental. Ideally, the body fighting the war should be authorized
to do so by the institutions of a constitutional democracy. Looser
forms of authorization are clearly possible; even a state that is not
overall legitimate might nonetheless be authorized by its polity to
fight wars of national defence. 



Authorization of this kind matters to *jus ad bellum* in two
ways. First, fighting a war without authorization constitutes an
additional wrong, which has to be weighed against the goods that
fighting will bring about, and must pass the proportionality and
necessity tests. When a government involves its polity in a war, it
uses the resources of the community at large, as well as its name, and
exposes it to both moral and prudential risks (Lazar forthcoming-b).
Doing this unauthorized is obviously deeply morally problematic. Any
form of undemocratic decision-making by governments is objectionable;
taking decisions of this magnitude without the population's
granting you the right to do so is especially wrong.



Second, authorization can allow the government to act on positive
reasons for fighting that would otherwise be unavailable. Consider the
claim that wars of national defence are in part justified by the
political interests of the citizens of the defending
state--interests, for example, in democratic participation or in
collective self-determination. A government may defend these
aggregated political interests only if it is authorized to do so.
Otherwise fighting would contravene the very interests in
self-determination that it is supposed to protect. But if it is
authorized, then that additional set of reasons supports fighting.



As a result, democratic states enjoy somewhat more expansive war
rights than non-democratic states and non-state movements. The latter
two groups cannot often claim the same degree of authorization as
democratic states. Although this might not vindicate the current bias
in international law towards states, it does suggest that it
corresponds to something more than the naked self-interest of the
framers of international law--which were, of course, states. This
obviously has significant implications for civil wars (see Parry
2016).


### 3.4 Proportionality



The central task of the proportionality constraint, recall, is to
identify reasons that tell in favour of fighting and those that tell
against it. Much of the latter task is reserved for the discussion of
*jus in bello* below, since it concerns weighing lives in
war.



Among the goods that help make a war proportionate, we have already
considered those in the just cause and others connected to just peace
and legitimate authority. Additionally, many also think that
proportionality can be swayed by reasonable partiality towards
one's own state and co-citizens. Think back to the political
interests that help justify national defence. If we were wholly
impartial, then we should choose the course that will best realise
people's political interests overall. So if fighting the
defensive war would undermine the political interests of the adversary
state's citizens more than it would undermine our own, then we
should refuse to fight. But this is not how we typically think about
the permission to resort to war: we are typically entitled to be
somewhat partial towards the political interests of our
co-citizens.



Some propose further constraints on what goods can count towards the
proportionality of a war. McMahan and McKim (1993) argued that
benefits like economic progress cannot make an otherwise
disproportionate war proportionate. This is probably true in practice,
but perhaps not in principle--that would require a kind of
lexical priority between lives taken and economic benefits, and
lexical priorities are notoriously hard to defend. After all, economic
progress saves lives. 



Some goods lack weight in *ad bellum* proportionality, not
because they are lexically inferior to other values at stake, but
because they are conditional in particular ways. Soldiers have
conditional obligations to fulfil their roles, grounded in their
contracts, oaths, and their co-citizens' legitimate
expectations. That carrying out an operation fulfils my oath gives me
a reason to perform that operation, which has to be weighed in the
proportionality calculation (Lazar 2015b). But these reasons cannot
contribute to *ad bellum* proportionality in the same way,
because they are conditional on the war as a whole being fought.
Political leaders cannot plausibly say: "were it not for all the
oaths that would be fulfilled by fighting, this war would be
disproportionate". This is because fighting counts as fulfilling
those oaths only if the political leader decides to take her armed
forces to war.



Another reason to differentiate between proportionality *ad
bellum* and *in bello* is that the relevant comparators
change for the two kinds of assessment. In a loose sense, we determine
proportionality by asking whether some option is better than doing
nothing. The comparator for assessing the war as a whole, then, is
*not fighting at all*, ending the war as a whole. That option
is not available when considering particular actions within the
war--one can only decide whether or not to perform this
particular action.


### 3.5 Last Resort (Necessity)



Are pre-emptive wars, fought in anticipation of an imminent enemy
attack, permissible? What of preventive wars, in which the assault
occurs prior to the enemy having any realistic plan of attack (see, in
general, Shue and Rodin 2007)? Neoconservatives have recently argued,
superficially plausibly, that the criterion of last resort can be
satisfied long before the enemy finally launches an attack (see
President 2002). The right answer here is boringly familiar. In
principle, of course this is possible. But, in practice, we almost
always overestimate the likelihood of success from military means and
overlook the unintended consequences of our actions. International law
must therefore retain its restrictions, to deter the kind of
overzealous implementation of the last-resort principle that we saw in
the 2003 invasion of Iraq (Buchanan and Keohane 2004; Luban 2004).



Another frequently discussed question: what does the
"last" in last resort really mean? The idea is simple, and
is identical to *in bello* necessity. Going to war must be
compared with the alternative available strategies for dealing with
the enemy (which also includes the various ways in which we could
submit). Going to war is literally a last resort when no other
available means has any prospect of averting the threat. But our
circumstances are not often this straitened. Other options always have
*some* chance of success. So if you have a diplomatic
alternative to war, which is less harmful than going to war, and is at
least as likely to avert the threat, then going to war is not a last
resort. If the diplomatic alternative is less harmful, as well as less
likely to avert the threat, then the question is whether the reduction
in expected harm is great enough for us to be required to accept the
reduction in likelihood of averting the threat. If not, then war is
your last
 resort.[13]


## 4. *Jus in Bello*


### 4.1 Walzer and his Critics



The traditionalist *jus in bello*, as reflected in
international law, holds that conduct in war must satisfy three
principles:


1. Discrimination: Targeting noncombatants is
 impermissible.[14]
2. Proportionality: Collaterally harming noncombatants (that is,
harming them foreseeably, but unintendedly) is permissible only if the
harms are proportionate to the goals the attack is intended to
 achieve.[15]
3. Necessity: Collaterally harming noncombatants is permissible only
if, in the pursuit of one's military objectives, the least
harmful means feasible are 
 chosen.[16]



These principles divide the possible victims of war into two classes:
combatants and noncombatants. They place no constraints on killing
 combatants.[17]
 But--outside of "supreme emergencies", rare
circumstances in which intentionally killing noncombatants is
necessary to avert an unconscionable threat--noncombatants may be
killed only unintendedly and, even then, only if the harm they suffer
is necessary and proportionate to the intended goals of the
 attack.[18]
 Obviously, then, much hangs on what makes one a combatant. This entry adopts a
conservative definition. Combatants are (most) members of the
organized armed forces of a group that is at war, as well as others
who directly participate in hostilities or have a continuous combat
function (for discussion, see Haque 2017). Noncombatants are
not combatants. There are, of course, many hard cases, especially in
asymmetric wars, but they are not considered here. "Soldier" is 
used interchangeably with "combatant" and
"civilian" interchangeably with
"noncombatant".



Both traditionalist just war theory and international law explicitly
license fighting in accordance with these constraints, regardless of
one's objectives. In other words, they endorse:



Combatant Equality: Soldiers who satisfy Discrimination,
Proportionality, and Necessity fight permissibly, regardless of what
they are fighting for.
 [19]



We discuss Proportionality and Necessity below; for now let us
concentrate on Michael Walzer's influential argument for
Discrimination and Combatant Equality, which has proved very
controversial.



Individual human beings enjoy fundamental rights to life and liberty,
which prohibit others from harming them in certain ways. Since
fighting wars obviously involves depriving others of life and liberty,
according to Walzer, it can be permissible only if each of the victims
has, "through some act of his own ... surrendered or lost
his rights" (Walzer 2006: 135). He then claims that,
"simply by fighting", all combatants "have lost
their title to life and liberty" (Walzer 2006: 136). First,
merely by posing a threat to me, a person alienates himself from me,
and from our common humanity, and so himself becomes a legitimate
target of lethal force (Walzer 2006: 142). Second, by participating in
the armed forces, a combatant has "allowed himself to be made
into a dangerous man" (Walzer 2006: 145), and thus surrendered
his rights. By contrast, noncombatants are "men and women with
rights, and... they cannot be used for some military purpose,
even if it is a legitimate purpose" (Walzer 2006: 137). This
introduces the concept of liability into the debate, which we need to
define carefully. On most accounts, that a person is liable to be
killed means that she is not wronged by being killed. Often this is
understood, as it was in Walzer, in terms of rights: everyone starts
out with a right to life, but that right can be forfeited or lost,
such that one can be killed without that right being violated or
infringed. Walzer and his critics all agreed that killing a person
intentionally is permissible only if either she has lost the
protection of her right to life, or if the good achieved thereby is
very great indeed, enough that, though she is wronged, it is not all
things considered wrong to kill her. Her right is permissibly
infringed. Walzer and his critics believe that such cases are very
rare in war, arising only when the alternative to intentionally
violating people's right to life is an imminent catastrophe on
the order of Nazi victory in Europe (this is an example of a supreme emergency).



These simple building blocks give us both Discrimination and Combatant
Equality--the former, because noncombatants, in virtue of
retaining their rights, are not legitimate objects of attack; the
latter, because all combatants lose their rights, regardless of what
they are fighting for: hence, as long as they attack only enemy
combatants, they fight legitimately, because they do not violate
anyone's rights.



These arguments have faced withering criticism. The simplest objection
against Combatant Equality brings it into conflict with
Proportionality (McMahan 1994; Rodin 2002; Hurka 2005). Unintended
noncombatant deaths are permissible only if proportionate to the
military objective sought. This means the objective is worth that much
innocent suffering. But military objectives are merely means to an
end. Their worth depends on how valuable the end is. How many innocent
deaths would be proportionate to Al Shabab's successfully
gaining control of Mogadishu now or to Iraq's capturing Kuwaiti
territory and oil reserves in 1991? In each case the answer is
obvious: none.



Proportionality is about weighing the evil inflicted against the evil
averted (Lee 2012). But the military success of unjust combatants does
not avert evil, it is itself evil. Evil intentionally inflicted can
only add to, not counterbalance, unintended evils. Combatant Equality
cannot be true.



Other arguments against Combatant Equality focus on Walzer's
account of how one loses the right to life. They typically start by
accepting his premise that permissible killing in war does not violate
the rights of the victims against being killed, at least for
intentional
 killing.[20]
 This contrasts with the view that sometimes people's rights to
life can be overridden, so war can be permissible despite infringing
people's rights. Walzer's critics then show that his
account of how we lose our right to life is simply not plausible.
Merely posing a threat to others--even a lethal threat--is
not sufficient to warrant the loss of one's fundamental rights,
because sometimes one threatens others' lives for very good
reasons (McMahan 1994). The soldiers of the Kurdish Peshmerga,
heroically fighting to rescue Yazidis from ISIL's genocidal
attacks, do not thereby lose their rights not to be killed by their
adversaries. Posing threats to others in the pursuit of a just aim,
where those others are actively trying to thwart that just aim, cannot
void or vitiate one's fundamental natural rights against being
harmed by those very people. The consent-based argument is equally
implausible as a general defence for Combatant Equality. Unjust
combatants have something to gain from waiving their rights against
lethal attack, if doing so causes just combatants to effect the same
waiver. And on most views, many unjust combatants have nothing to
lose, since by participating in an unjust war they have at least
weakened if not lost those rights already. Just combatants, by
contrast, have something to lose, and nothing to gain. So why would
combatants fighting for a just cause consent to be harmed by their
adversaries, in the pursuit of an unjust end?



Walzer's case for Combatant Equality rests on showing that just
combatants lose their rights to life. His critics have shown that his
arguments to this end fail. So Combatant Equality is false. But they
have shown more than this. Inspired by Walzer to look at the
conditions under which we lose our rights to life, his critics have
made theoretical advances that place other central tenets of *jus
in bello* in jeopardy. They argued, *contra* Walzer, that
posing a threat is not sufficient for liability to be killed (McMahan
1994, 2009). But they also showed that posing the threat oneself is
not necessary for liability either. This is more controversial, but
revisionists have long argued that liability is grounded, in war as
elsewhere, in one's responsibility for contributing to a
wrongful threat. The US president, for example, is responsible for a
drone strike she orders, even though she does not fire the
weapon herself.



As many have noted, this argument undermines Discrimination (McMahan
1994; Arneson 2006; Fabre 2012; Frowe 2014). In many states,
noncombatants play an important role in the resort to military force.
In modern industrialized countries, as much as 25 per cent of the
population works in war-related industries (Downes 2006: 157-8;
see also Gross 2010: 159; Valentino et al. 2010: 351); we provide the
belligerents with crucial financial and other services; we support and
sustain the soldiers who do the fighting; we pay our taxes and in
democracies we vote. Our contributions to the state's capacity
over time give it the strength and support to concentrate on
 war.[21]
 If the state's war is unjust, then many noncombatants are
responsible for contributing to wrongful threats. If that is enough
for them to lose their rights to life, then they are permissible
targets.



McMahan (2011a) has sought to avert this troubling implication of his
arguments by contending that almost all noncombatants on the unjust
side (unjust noncombatants) are less responsible than all unjust
combatants. But this involves applying a double standard, talking up
the responsibility of combatants, while talking down that of
noncombatants, and mistakes a central element in his account of
liability to be killed. On his view, a person is liable to be killed
in self- or other-defence in virtue of being, of those able to bear an
unavoidable and indivisible harm, the one who is most responsible for
this situation coming about (McMahan 2002, 2005b). Even if
noncombatants are only *minimally* responsible for their
states' unjust wars--that is, they are not blameworthy,
they merely voluntarily acted in a way that foreseeably contributed to
this result--on McMahan's view this is enough to make them
liable to be killed, if doing so is necessary to save the lives of
wholly innocent combatants and noncombatants on the just side (see
especially McMahan 2009: 225).



One response is to reject this comparative account of how
responsibility determines liability, and argue for a non-comparative
approach, according to which one's degree of responsibility must
be great enough to warrant such a severe derogation from one's
fundamental rights. But if we do this, we must surely concede that
many combatants on the unjust side are not sufficiently responsible
for unjustified threats to be liable to be killed. Whether through
fear, disgust, principle or ineptitude, many combatants are wholly
ineffective in war, and contribute little or nothing to threats posed
by their side. The much-cited research of S. L. A. Marshall claimed
that only 15-25 per cent of Allied soldiers in the Second World
War who could have fired their weapons did so (Marshall 1978). Most
soldiers have a natural aversion to killing, which even intensive
psychological training may not overcome (Grossman 1995). Many
contribute no more to unjustified threats than do noncombatants. They
also lack the "*mens rea*" that might make
liability appropriate in the absence of a significant causal
contribution. They are not often blameworthy. The loss of their right
to life is not a fitting response to their conduct.



If Walzer is right that in war, outside of supreme emergencies, we may
intentionally kill only people who are liable to be killed, and if a
significant proportion of unjust combatants and noncombatants are
responsible to the same degree as one another for unjustified threats,
and if liability is determined by responsibility, then we must decide
between two unpalatable alternatives. If we set a high threshold of
responsibility for liability, to ensure that noncombatants are not
liable to be killed, then we will also exempt many combatants from
liability. In ordinary wars, which do not involve supreme emergencies,
intentionally killing such non-liable combatants would be
impermissible. This moves us towards a kind of pacifism--though
warfare can in principle be justified, it is so hard to fight without
intentionally killing the non-liable that in practice we must be
pacifists (May 2015). But if we set the threshold of responsibility
low, ensuring that all unjust combatants are liable, then many
noncombatants will be liable too, thus rendering them permissible
targets and seriously undermining Discrimination. We are torn between
pacifism on the one hand, and realism on the other. This is the
"responsibility dilemma" for just war theory (Lazar
2010).


### 4.2 Killing Combatants



Just war theory has meaning only if we can explain why killing some
combatants in war is allowed, but we are not thereby licensed to kill
everyone in the enemy state. Here the competing forces of realism and
pacifism are at their most compelling. It is unsurprising, therefore,
that so much recent work has focused on this topic. We cannot do
justice to all the arguments here, but will instead consider three kinds of
response: all-out revisionist; moderate traditionalist; and all-out
traditionalist.



The first camp faces two challenges: to justify intentionally killing
apparently non-liable unjust combatants; but to do this without
reopening the door to Combatant Equality, or indeed further
undermining Discrimination. Their main move is to argue that, despite
appearances, all and only unjust combatants are in fact liable to be
killed.



McMahan argues that liability to be killed need not, in fact,
presuppose responsibility for an unjustified threat. Instead, unjust
combatants' responsibility for just combatants' reasonable
beliefs that they are liable may be enough to ground forfeiture of their rights
(McMahan 2011a). Some argue that combatants' responsibility for
being in the wrong place at the wrong time is enough (likening them to
voluntary human
 shields).[22]
 More radically still, some philosophers abandon the insistence on
individual responsibility, arguing that unjust combatants are
collectively responsible for contributing to unjustified threats, even
if they are individually ineffective (or even counterproductive) (Kamm
2004; Bazargan 2013).



Lazar (forthcoming-a) suggests these arguments are
unpersuasive. Complicity might be relevant to the costs one is
required to bear in war, but most liberals will baulk at the idea of
losing one's right to life in virtue of things that other people
did. And if combatants can be complicitously liable for what their
comrades-in-arms did, then why shouldn't noncombatants be
complicitously liable also?



Blameworthy responsibility for other people's false beliefs does
seem relevant to the ethics of self- and other-defence. That said,
consider an idiot who pretends to be a suicide bomber as a prank, and
is shot by a police officer (Ferzan 2005; McMahan 2005c). Is killing
him objectively permissible? It seems doubtful. The officer's justified
belief that the prankster posed a threat clearly diminishes the
wrongfulness of killing him (Lazar 2015a). And certainly the
prankster's fault excuses the officer of any guilt. But killing
the prankster still seems objectively wrong. Even if someone's
blameworthy responsibility for false beliefs could make killing him
objectively permissible, most philosophers agree that many unjust
combatants are not to blame for the injustice of their wars (McMahan
1994; Lazar 2010). And it is *much* less plausible that
blameless responsibility for beliefs can make one a permissible
target. Even if it did, this would count in favour of moderate
Combatant Equality, since most just combatants are also blamelessly
responsible for unjust combatants' reasonable beliefs that they
are liable to be killed.



Moderate traditionalists think we can avoid the realist and pacifist
horns of the responsibility dilemma only by conceding a moderate form
of Combatant Equality. The argument proceeds in three stages. First,
endorse a non-comparative, high threshold of responsibility for
liability, such that most noncombatants in most conflicts are not
responsible enough to be liable to be killed. This helps explain why
killing civilians in war is so hard to justify. Of course, it also
entails that many combatants will be innocent too. The second step,
then, is to defend the principle of *Moral Distinction*,
according to which killing civilians is worse than killing soldiers.
This is obviously true if the soldiers are liable and the civilians
are not. But the challenge is to show that killing *non-liable*
civilians is worse than killing *non-liable* soldiers. If we
can do that, then the permissibility of intentionally killing
non-liable soldiers does not entail that intentionally killing
non-liable noncombatants is permissible. Of course, one might still
argue that, even if Moral Distinction is true, we should endorse
pacifism. But, and this is the third stage, the less seriously
wrongful some act is, the lesser the good that must be realised by
performing that act, for it to be all things considered permissible.
If intentionally killing innocent combatants is not the worst kind of
killing one can do, then the good that must be realised for it to be
all things considered permissible is less than is the case for, for
example, intentionally killing innocent civilians, which philosophers
tend to think can be permissible only in a supreme emergency. This
could mean that intentionally killing innocent soldiers is permissible
even in the ordinary circumstances of war.



Warfare can be justified, then, by a combination of liability and
lesser evil grounds. Some unjust combatants lose their rights not to
be killed. Others' rights can be overridden without that
implying that unjust noncombatants' rights may be overridden
too. We can reject the pacifist horn of the responsibility dilemma.
But a moderate Combatant Equality is likely to be true: since killing
innocent combatants is not the worst kind of killing, it is
correspondingly easier for unjust combatants to justify using lethal
force (at least against just combatants). This increases the range of
cases in which they can satisfy Discrimination, Proportionality, and
Necessity, and so fight permissibly.



Much hangs, then, on the arguments for Moral Distinction. Some focus
on why killing innocent noncombatants is especially wrongful; others
on why killing innocent combatants is not so bad. This section
considers the second kind of argument, returning to the first in the
next section.



The revisionists' arguments mentioned above might not ground
liability, but do perhaps justify *some* reason to prefer
harming combatants. Combatants can better avoid harm than
noncombatants. Combatants surely do have *somewhat* greater
responsibilities to bear costs to avert the wrongful actions of their
comrades-in-arms than do noncombatants. And the readiness of most
combatants to fight--regardless of whether their cause is
just--likely means that even just combatants have somewhat
muddied status relative to noncombatants. They conform to their
opponents' rights only by accident. They have weaker grounds for
complaint when they are wrongfully killed than do noncombatants, who
more robustly respect the rights of others (on robustness and respect,
see Pettit 2015).



Additionally, when combatants kill other combatants, they typically
believe that they are doing so permissibly. Most often they believe
that their cause is just, and that this is a legitimate means to bring
it about. But, insofar as they are lawful combatants, they will also
believe that international law constrains their actions, so that by
fighting in accordance with it they are acting permissibly. Lazar
(2015c) argues that killing people when you know that doing so is
objectively wrong is more seriously objectionable than doing so when
you reasonably believe that you are acting permissibly.



The consent-based argument for Combatant Equality fails because of its
empirical, not its normative premise. If combatants in fact waived
their rights not to be killed by their adversaries, even when fighting
a just war, then that would clearly affect their adversaries'
reasons for action, reducing the wrongfulness of killing anyone who
had waived that right. The problem is that they have not waived their
rights not to be killed. However, they often do offer a more limited
implicit waiver of their rights. The purpose of having armed forces,
and the intention of many who serve in them, is to protect civilians
from the predations of war. This means both countering threats to and
drawing fire away from them. Combatants interpose themselves between
the enemy and their civilian compatriots, and fight on their
compatriots' behalf. If they abide by the laws of war, they
clearly distinguish themselves from the civilian population, wearing a
uniform and carrying their weapons openly. They implicitly say to
their adversaries: "you ought to put down your weapons. But if
you are going to fight, then *fight us*". This
constitutes a limited waiver of their rights against harm. Like a full
waiver, it alters the reasons confronting their
adversaries--under these circumstances, other things equal it is
worse to kill the noncombatants. Of course, in most cases unjust
combatants ought simply to stop fighting. But this conditional waiver
of their opponents' rights means that, if they are not going to
put down arms, they do better to target combatants than
noncombatants.



Of course, one might think that in virtue of their altruistic
self-sacrifice, just combatants are actually the *least*
deserving of the harms of war (Tadros 2014). But, first, warfare is
not a means for ensuring that people get their just deserts. More
importantly, given that their altruism is specifically intended to
draw fire away from their compatriot noncombatants, it would be
perverse to treat this as a reason to do precisely what they are
trying to prevent. 



These arguments and others suggest that killing innocent combatants is
not the worst kind of killing one can do. It might therefore be all
things considered permissible in the ordinary circumstances of war,
provided enough good is achieved thereby. If unjust combatants attack
only just combatants, and if they achieve some valuable objective by
doing so--defence of their comrades, their co-citizens, or their
territory--they therefore might fight permissibly, even though
they violate the just combatants' rights (Kamm 2004; Hurka 2005;
Kamm 2005; Steinhoff 2008; Lazar 2013). At least, it is more plausible
that they can fight permissibly than if we regarded every just
combatant's death as equivalent to the worst kind of murder.
This does not vindicate Combatant Equality--it simply shows that,
more often than one might think, unjust combatants can fight
permissibly. Add to that the fact that all wars are morally
heterogeneous, involving just and unjust phases (Bazargan 2013), and
we quickly see that even if Combatant Equality in the laws of war
lacks fundamental moral foundations, it is a sensible approximation of
the truth.



Some philosophers, however, seek a more robust defence of Combatant
Equality. The three most prominent lines are institutionalist. A
contractualist argument (Benbaji 2008, 2011) starts by observing that
states (and their populations) need disciplined armies for the
purposes of national defence. If soldiers always had to decide for
themselves whether a particular war was just, many states could not
raise armies when they need to. They would be unable to deter
aggression. All states, and all people, benefit from an arrangement
whereby individual combatants waive their rights not to be killed by
one another--allowing them to obey their state's commands
without second-guessing every deployment. Combatants tacitly consent
to waive their rights in this way, given common knowledge that
fighting in accordance with the laws of war involves such a waiver.
Moreover, their assent is "morally effective" because it
is consistent with a fair and optimal contract among states.



International law does appear to change the moral standing of
combatants. If you join the armed forces of a state, you know that, at
international law, you thereby become a legitimate target in armed
conflict. This has to be relevant to the wrongfulness of harming you,
even if you are fighting for a just cause. But Benbaji's
argument is more ambitious than this. He thinks that soldiers waive
their rights not to be killed by one another--not the limited,
conditional waiver described above, but an outright waiver, that
absolves their adversaries of any wrongdoing (though it does not so
absolve their military and political leaders).



The first problem with this proposal is that it rests on contentious
empirical speculation about whether soldiers in fact consent in this
way. But setting that aside, second, it is radically statist, implying
that international law simply doesn't apply to asymmetric
conflicts between states and non-state actors, since the latter are
not part of the appropriate conventions. This gives international law
shallow foundations, which fail to support the visceral outrage that
breaches of international law typically evoke. It also suggests that
states that either don't ratify major articles of international
law, or that withdraw from agreements, can escape its strictures. This
seems mistaken. Third, we typically regard waivers of fundamental
rights as reversible when new information comes to light. Why
shouldn't just combatants be allowed to withdraw their
rights-waiver when they are fighting a just war? Many regard the right
to life as inalienable; even if we deny this, we must surely doubt
whether you can alienate it once and for all, under conditions of
inadequate information. Additionally, suppose that you want to join
the armed forces only to fight a specific just war (McMahan 2011b).
Why should you waive your rights against harm in this case, given that
you plan only to fight now? Fourth, and most seriously, even if
Benbaji's argument explained why killing combatants in war is
permissible regardless of the cause you are serving, it cannot explain
why unintentionally killing noncombatants as a side-effect of
one's actions is permissible. By joining the armed forces of
their state, soldiers at least do *something* that implies
their consent to the regime of international law that structures that
role. But noncombatants do not consent to this regime. Soldiers
fighting for unjust causes will inevitably kill many innocent
civilians. If those deaths cannot be rendered proportionate, then
Combatant Equality does not hold.



The second institutionalist argument starts from the belief that we
have a duty to obey the law of our legitimate state. This gives unjust
combatants, ordered to fight an unjust war, some reason to obey those
orders. We can ground this in different ways. Estlund (2007) argues
that the duty to obey orders derives from the epistemic authority of
the state--it is more likely than an individual soldier to know
whether this war is just (see Renzo 2013 for criticism); Cheyney Ryan
(2011) emphasizes the democratic source of the state's
authority, as well as the crucial importance of maintaining civilian
control of the military. These are genuine moral
reasons that should weigh in soldiers' deliberations. But are
they really weighty enough to ground Combatant Equality? It seems doubtful.
They cannot systematically override unjust combatants'
obligations not to kill innocent people. This point stands regardless
of whether these reasons weigh in the balance, or are exclusionary
reasons that block others from being considered (Raz 1985). The rights
of innocent people not to be killed are the weightiest, most
fundamental rights around. For some other reason to outweigh them, or
exclude them from deliberation, it would have to be extremely
powerful. Combatants' obligations to obey orders simply are not
weighty enough--as everyone recognises with respect to obedience
to unlawful *in bello* commands (McMahan 2009: 66ff).



Like the first argument, the third institutionalist argument grounds
Combatant Equality in its long-term results. But instead of focusing
on states' ability to defend themselves, it emphasizes the
importance of limiting the horrors of war, given that we know that people
deceive themselves about the justice of their cause (Shue 2008, 2010;
Dill and Shue 2012; Shue 2013; Waldron 2016). Since combatants and
their leaders almost always believe themselves to be in the right, any
injunction to unjust combatants to lay down their arms would simply be
ignored, while any additional permissions to harm noncombatants would
be abused by both sides. In almost all wars, it is *sufficient*
to achieve military victory that you target only combatants. If doing
this will minimize wrongful deaths in the long run, we should enjoin
that all sides, regardless of their aims, respect Discrimination.
Additionally, while it is extremely difficult to secure international
agreement even about what in fact constitutes a just cause for war
(witness the controversy over the Rome statute on crimes of aggression, which took many years of negotiation before diplomats agreed an uneasy compromise), the traditionalist principles
of *jus in bello* already have broad international support.
They are hard-won concessions that we should abandon only if we are
sure that the new regime will be an improvement (Roberts 2008).



Although this argument is plausible, it doesn't address the same
question as the act-focused arguments that preceded it. One thing we
can ask is: given a particular situation, what ought we to do? How
ought soldiers to act in Afghanistan, or Mali, or Syria, or Somalia?
And when we ask this question, we shouldn't start by assuming
that we or they will obviously fail to comply with any exacting moral
standards that we might propose (Lazar 2012a; Lazar and Valentini
forthcoming). When considering our own actions, and those of people over whom
we have influence, we should select from all the available options,
not rule some out because we know ourselves to be too immoral to take
them. When designing institutions and laws, on the other hand, of
course we should think about how people are likely to respond to them.
We need to answer both kinds of questions: what *really* ought
I to do? And what should the laws be, given my and others'
predictable frailty?



A moderate Combatant Equality, then, is the likely consequence of
avoiding the pacifist horn of the responsibility dilemma. To show that
killing in war is permissible, we need to show that intentionally
killing innocent combatants is not as seriously wrongful as
intentionally killing innocent noncombatants. And if killing innocent
combatants is not the worst kind of killing, it can more plausibly be
justified by the goods achieved in ordinary wars, outside of supreme
emergencies. On this view, contrary to the views of both Walzer and
his critics, much of the intended killing in justified wars is
permissible not because the targets are liable to be killed, but
because infringing their rights is a permissible lesser evil. But this
principle applies regardless of whether you are on the just or the
unjust side. This in turn increases the range of cases in which
combatants fighting on the unjust side will be able to fight
permissibly: instead of needing to achieve some good comparable to
averting a supreme emergency in order to justify infringing the rights
of just combatants, they need only achieve more prosaic kinds of
goods, since these are not the worst kinds of rights infringements. So
unjust combatants' associative duties to protect one another and
their compatriots, their duties to obey their legitimate governments,
and other such considerations, can sometimes make intentionally
killing just combatants a permissible lesser evil, and unintentionally
killing noncombatants proportionate. This means that the existing laws
of war are a closer approximation of combatants' true moral
obligations than many revisionists think. Nonetheless, much of the
killing done by unjust combatants in war is still objectively
wrong.


### 4.3 Sparing Civilians



The middle path in just war theory depends on showing that killing
civilians is worse than killing soldiers. This section discusses
arguments to explain why killing civilians is distinctly
objectionable. We discuss the significance of *intentional*
killing when considering proportionality, below.



These arguments are discussed at great length in Lazar (2015c), and
are presented only briefly here. They rest on a key point: Moral
Distinction says that killing civilians is worse than killing
soldiers. It *does not* say that killing civilians is worse
than killing soldiers, *other things equal*. Lazar
holds that stronger principle but does not think that the intrinsic
differences between killing civilians and killing soldiers--the
properties that are *necessarily* instantiated in those two
kinds of killings--are weighty enough to provide Moral
Distinction with the kind of normative force needed to protect
noncombatants in war. That protection depends on mobilising multiple
foundations for Moral Distinction, which include many properties that
are *contingently but consistently* instantiated in acts that
kill civilians and kill soldiers, which make killing civilians worse.
We cannot ground Moral Distinction in any one of these properties
alone, since each is susceptible to counterexamples. But when they are
all taken together, they justify a relatively sharp line between
harming noncombatants and harming combatants. There are, of course,
hard cases, but these must be decided by appealing to the salient
underlying properties rather than to the mere fact of membership in
one group or the other.



First, at least deliberately killing civilians in war usually fails
even the most relaxed interpretation of the necessity constraint. This
is not always true--killing is necessary if it is effective at
achieving your objective, and no other effective options are
available. Killing civilians sometimes meets this description. It is
often effective: the blockade of Germany helped end the first world
war, though it may have caused as many as half a million civilian
deaths; Russian targeting of civilians in Chechnya reduced Russian
combatant casualties (Lyall 2009); Taliban anti-civilian tactics have
been effective in Afghanistan. And these attacks are often the last
recourse of groups at war (Valentino 2004); when all other options
have failed or become too costly, targeting civilians is relatively
easy to do. Indeed, as recent terrorist attacks have shown (Mumbai and
Paris, for example), fewer than ten motivated gunmen with basic
weaponry can bring the world's most vibrant cities screeching to
a halt. So, killing civilians *can* satisfy the necessity
constraint. Nonetheless, attacks on civilians are often wholly wanton,
and there is a special contempt expressed in killing innocent people
either wantonly or for its own sake. At least if you have
*some* strategic goal in sight, you might believe that
something is at stake that outweighs the innocent lives taken. Those
who kill civilians pointlessly express their total disregard for their
victims in doing so.



Second, even when killing civilians is effective, it is usually so
*opportunistically* (Quinn 1989; Frowe 2008; Quong 2009; Tadros
2011). That is, the civilians' suffering is used as a means to
compel their compatriots and their leaders to end their war. Sieges
and aerial bombardments of civilian population centres seek to break
the will of the population and of their government. Combatants, by
contrast, are almost always killed *eliminatively*--their
deaths are not used to derive a benefit that could not be had without
using them in this way; instead they are killed to solve a problem
that they themselves pose. This too seems relevant to the relative
wrongfulness of these kinds of attacks. Of course, at the strategic
level every death is intended as a message to the enemy leadership,
that the costs of continuing to fight outweigh the benefits. But at
the tactical level, where the actual killing takes place, soldiers
typically kill soldiers eliminatively, while they kill civilians
opportunistically. If this difference is morally important, as many
think, and if acts that kill civilians are opportunistic much more
often than are acts that kill soldiers, then acts that kill civilians
are, in general, worse than acts that kill soldiers. This lends
further support to Moral Distinction.



Third, as already noted above, the agent's beliefs can affect
the objective seriousness of her act of killing. Killing someone when
you have solid grounds to think that doing so is objectively
permissible wrongs that person less seriously than when your epistemic
basis for harming them is weaker. More precisely, killing an innocent
person is more seriously wrongful the more reason the killer had to
believe that she was not liable to be killed (Lazar 2015a).



Last, in ordinary thinking about the morality of war, the two
properties most commonly cited to explain the distinctive wrongfulness
of harming civilians, after their innocence, are their vulnerability
and their defencelessness. Lazar (2015c) suspects that the duties to
protect the vulnerable and not to harm the defenceless are almost as
basic as the duty not to harm the innocent. (Note that these duties
apply only when their object is morally innocent.) Obviously, on any
plausible analysis, civilians are more vulnerable and defenceless than
soldiers, so if killing innocent people who are more vulnerable and
defenceless is worse than killing those who are less so, then killing
civilians is worse than killing soldiers.



Undoubtedly soldiers are also often vulnerable too--one thinks of
the "Highway of Death", in Iraq 1991, when American forces
destroyed multiple armoured divisions of the Iraqi army, which were
completely unprotected (many of the personnel in those divisions
escaped into the desert). But this example just shows that killing
soldiers, when they are vulnerable and defenceless, is harder to
justify than when they are not. Provided the empirical claim that
soldiers are less vulnerable and defenceless than civilians is true,
this simply supports the case for Moral Distinction.


### 4.4 Proportionality



Holding the principle of Moral Distinction allows one to escape the
realist and pacifist horns of the responsibility dilemma, while still
giving responsibility its due. Even revisionists who deny moderate
Combatant Equality could endorse Moral Distinction, and thereby
retain the very plausible insight that it is worse to kill just
noncombatants than to kill just combatants. And, if they are to
account for most people's considered judgements about war, even
pacifists need some account of why killing civilians is worse than
killing soldiers.



However, Moral Distinction is not Discrimination. It is a comparative
claim, and it says nothing about intentions. Discrimination, by
contrast, prohibits intentionally attacking noncombatants, except in
supreme emergencies. It is the counterpart of Proportionality, which
places a much weaker bar on unintentionally killing noncombatants.
Only a terrible crisis could make it permissible to intentionally
attack noncombatants. But the ordinary goods achieved in individual
battles can justify unintentional killing. What justifies this radical
distinction?



This is one of the oldest questions in normative ethics (though for
the recent debate, see Quinn 1989; Rickless 1997; McIntyre 2001;
Delaney 2006; Thomson 2008; Tadros 2015). On most accounts, those who
intend harm to their victims show them a more objectionable kind of disrespect
than those who unavoidably harm them as a side-effect. Perhaps the
best case for the significance of intentions is, first, in a general
argument that mental states are relevant to objective permissibility
(Christopher 1998; see also Tadros 2011). And second, we need a rich
and unified theoretical account of the specific mental states that
matter in this way, into which intentions fit. It may be that the
special prohibition of intentional attacks on civilians overstates the
moral truth. Intentions do matter. Other things equal, intentional
killings are worse than unintended killings (though some unintended
killings that are wholly negligent or indifferent to the victim are
nearly as bad as intentional killings). But the difference between
them is not categorical. It cannot sustain the contrast between a
near-absolute prohibition on one hand, and a sweeping permission on
the other.



Of course, this is precisely the kind of nuance that would be
disastrous if implemented in international law or if internalized as a
norm by combatants. Weighing lives in war is informationally
incredibly demanding. Soldiers need a principle they can apply.
Discrimination is that principle. It is not *merely* a rule of
thumb, since it entails something that is morally
grounded--killing civilians is worse than killing soldiers. But
it is *also* a rule of thumb, because it draws a starker
contrast between intended and unintended killing than is intrinsically
morally justified.



As already noted, proportionality and necessity contain within them
almost every other question in the ethics of war; we now consider two
further points.



First, proportionality in international law is markedly different from
the version of the principle that first-order moral theory supports.
At law, an act of war is proportionate insofar as the harm to
civilians is not excessive in relation to the concrete and direct
military advantage realized thereby. As noted above, in first-order
moral terms, this is unintelligible. But there might be a better
institutional argument for this neutral conception of proportionality.
Proportionality calculations involve many substantive value
judgements--for example, about the significance of moral status,
intentions, risk, vulnerability, defencelessness, and so on. These are
all highly controversial topics. Reasonable disagreement abounds. Many
liberals think that coercive laws should be justified in terms that
others can reasonably accept, rather than depending on controversial
elements of one's overarching moral theory (Rawls 1996: 217).
The law of armed conflict is coercive; violation constitutes a war
crime, for which one can be punished. Of course, a more complex law
would not be justiciable, but we also have principled grounds for not
basing international law on controversial contemporary disputes in
just war theory. Perhaps the current standard can be endorsed from
within a wider range of overarching moral theories than could anything
closer to the truth.



Second, setting aside the law and focusing again on morality, many
think that responsibility is crucial to thinking about
proportionality, in the following way. Suppose the Free Syrian Army
(FSA) launches an assault on Raqqa, stronghold of ISIL. They predict
that they will cause a number of civilian casualties in their assault,
but that this is only because ISIL has chosen to operate from within a
civilian area, forcing people to be "involuntary human
shields". Some think that ISIL's responsibility for
putting those civilians at risk allows the FSA to give those
civilians' lives less weight in their deliberations than would
be appropriate if ISIL had not used them as human shields (Walzer
2009; Keinon 2014).



But one could also consider the following: Even if ISIL is primarily
at fault for using civilians as cover, why should this mean that those
civilians enjoy weaker protections against being harmed? We typically
think that one should only lose or forfeit one's rights through
*one's own* actions. But on this argument, civilians
enjoy weaker protections against being killed through no fault or
choice of their own. Some might think that more permissive standards
apply for involuntary human shields because of the additional value of
deterring people from taking advantage of morality in this kind of way
(Smilansky 2010; Keinon 2014). But that argument seems oddly circular:
we punish people for taking advantage of our moral restraint by not
showing moral restraint. What's more, this changes the act from
one that foreseeably kills civilians as an unavoidable side-effect of
countering the military threat to one that kills those civilians as a
means to deter future abuses. This instrumentalizes them in a way that
makes harming them still harder to justify.


### 4.5 Necessity



The foregoing considerations are all also relevant to necessity. They
allow us to weigh the harms at stake, so that we can determine whether
the morally weighted harm inflicted can be reduced at a reasonable
cost to the agents. The basic structure of necessity is the same
*in bello* as it is *ad bellum*, though obviously the
same differences in substance arise as for proportionality. Some
reasons apply only to *in bello* necessity judgements, not to
*ad bellum* ones, because they are conditional on the
background assumption that the war as a whole will continue. This
means that we cannot reach judgements of the necessity of the war as a
whole by simply aggregating our judgements about the individual
actions that together constitute the war.



For example, *in bello* one of the central questions when
applying the necessity principle is: how much risk to our own troops
are we required to bear in order to minimize harms to the innocent?
Some option can be necessary simply in virtue of the fact that it
saves some of our combatants' lives. *Ad bellum*,
evaluating the war as a whole, we must of course consider the risk to
our own combatants. But we do so in a different way--we ask
whether the goods achieved by the war as a whole will justify putting
our combatants at risk. We don't then count among the goods
achieved by the war the fact that multiple actions within the war will
save the lives of individual combatants. We cannot count averting
threats that will arise only if we decide to go to war among the goods
that justify the decision to go to war.



This relates directly to the largely ignored requirement in
international law that combatants must 



> 
> take all feasible precautions in the choice of means and methods of
> attack with a view to avoiding, and in any event to minimizing,
> incidental loss of civilian life, injury to civilians and damage to
> civilian objects. (Geneva Convention, Article 57, 2(a)(ii))
> 



This has deep moral foundations: combatants in war are morally
*required* to reduce the risk to innocents until doing so
further would involve an unreasonably high cost to them, which they
cannot be required to bear. Working out when that point is reached
involves thinking through: soldiers' role-obligations to assume
risks; the difference between doing harm to civilians and allowing it
to happen to oneself or one's comrades-in-arms; the importance
of associative duties to protect one's comrades; and all the
considerations already adduced in favour of Moral Distinction. This
calculus is very hard to perform. My own view is that combatants ought
to give significant priority to the lives of civilians (Walzer and
Margalit 2009; McMahan 2010b). This is in stark contrast to existing
practice (Luban 2014).


## 5. The Future of Just War Theory



Much recent work has used either traditionalist or revisionist just
war theory to consider new developments in the practice of warfare,
especially the use of drones, and the possible development of
autonomous weapons systems. Others have focused on the ethics of
non-state conflicts, and asymmetric wars. Very few contemporary wars
fit the nation-state model of the mid-twentieth century, and conflicts
involving non-state actors raise interesting questions for legitimate
authority and the principle of Discrimination in particular (Parry
2016). A third development, provoked by the terrible failure to plan
ahead in Iraq and Afghanistan, is the wave of reflection on the
aftermath of war. This topic, *jus post bellum*, is addressed
separately.



As to the philosophical foundations of just war theory: the
traditionalist and revisionist positions are now well staked out. But
the really interesting questions that remain to be answered should be
approached without thinking in terms of that split. Most notably, 
*political* philosophers may have something more to contribute
to the just war theory debate. It would be interesting, too, to think
with a more open mind about the institutions of international law
(nobody has yet vindicated the claim that the law of armed conflict
has authority, for example), and also about the role of the military
within nation-states, outside of wartime (Ryan 2016).



The collective dimensions of warfare could be more fully
explored. Several philosophers have considered how soldiers "act
together" when they fight (Zohar 1993; Kutz 2005; Bazargan
2013). But few have reflected on whether group agency is present and
morally relevant in war. And yet it is superficially very natural to
discuss wars in these terms, especially in evaluating the war as a
whole. When the British parliament debated in late 2015 whether to
join the war against ISIL in Syria and Iraq, undoubtedly each MP was
thinking also about what *she* ought to do. But most of them
were asking themselves what *the United Kingdom* ought to
do. This group action might be wholly reducible to the individual
actions of which it is composed. But this still raises interesting
questions: in particular, how should I justify my actions, as an
individual who is acting on behalf of the group? Must I appeal only to
reasons that apply to me? Or can I act on reasons that apply to the
group's other members or to the group as a whole? And can I
assess the permissibility of my actions without assessing the group
action of which they are part? Despite the prominence of collectivist
thinking in war, discussion of war's group morality is very much
in its infancy.