Excusing Illegal Use of Force: From Illegal but Legitimate to Legal Because it is Legitimate?

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The US missile strikes on Syria have, inter alia, revived the debates on humanitarian intervention, the argument of ‘illegal but legitimate’ and more generally on the exceptions to the prohibition of the use of force. For some examples see here, here and here. Some contributors have pointed out that the US did not even try to bring this action within the ambit of the Charter rules on the use of force, and that the absence of Charter-based arguments may even be a good thing as it preserves the strength of Article 2(4). Others have cautioned that the strength of the rules on the use of force might nevertheless be undermined, as singular ‘exceptional’ cases result in a pattern.

This post argues that, analogous to the concept of defences in municipal legal systems, international law on the use of force should adopt a systematic distinction between justifications and excuses. As responses to the US missile attack in Syria demonstrate, the two concepts are conflated. The result is that legality is often assessed on the basis of excuses. If the trend of conflation continues, the controversial doctrine of ‘illegal but legitimate’ will move toward an even more controversial doctrine of ‘legal because it is legitimate’.

Justifications are legally-warranted exceptions to the general prohibition. As such, they are a way out of illegality. Excuses, on the other hand, are not a way out of illegality, but act as mitigating circumstances that preclude responsibility for an otherwise illegal conduct. Under some circumstances, breaching the law may indeed be the choice of a lesser evil. As noted by Vaughan Lowe in his 1999 EJIL article, a legal system may wish to provide a defence for emergency drivers who breach the speed limit on the way to hospital. There are two ways of achieving this goal. One way is to give them an explicit authorization to breach the speed limit. The other one, however, does not authorize speeding, but rather ensures that emergency drivers are not prosecuted upon such a breach of traffic rules. The first (justification) relaxes the norm itself and may well result in wider disobeying of the speed limit than the second, which merely provides for a carefully weighed excuse of culpability where the norm was doubtlessly breached. In other words, it is better if the general norm is strong and ‘catches’ more violators whose excuses are then considered on a case-by-case basis. I elaborate on these issues in more details in this 2015 concept paper. In the present context, might the ‘emergency driver logic’ apply to the US strike in Syria? Even if it did, it would not make this action legal. Possibly, the US could only escape responsibility for this internationally wrongful act. 

The Charter justifications and extra-Charter excuses

The Charter regulation on the use of force adopts a clear logic of justifications. Article 2(4) spells out the prima facie prohibition, while Articles 39+42 and Article 51 give legal authorization for a departure from this general rule. When properly used pursuant to Articles 39+42 or Article 51, force in international law is not illegal. Because it is justified.

The humanitarian intervention and R2P doctrines can, in principle, fit into the Charter justifications, but not as independent legal concepts. They can operate via Articles 39+42. The humanitarian intervention and R2P doctrines can underlie political decisions for Security Council’s authorization of force. But what if compelling moral reasons for an intervention exist and the Security Council does not act? This is the ‘illegal but legitimate’ type of reasoning, which was advanced most prominently in the situation of Kosovo. It has not always been popular in international legal scholarship, but it reflects the very logic of excuses.

The legitimacy criteria for humanitarian intervention and other instances of extra-Charter use of force, which have been developed by several scholars and governments, can thus only be considered as criteria for assessing the plausibility of an excuse for an otherwise illegal use of force. But they do not serve as justifications. In the present context, even the statement of the US Permanent Representative to the UN, Nikki Haley, builds on the logic of excuse rather than justification, as does the statement of President Donald Trump.

Was the US missile attack excusable? In the decentralized international legal system, it is ultimately – for the most part – other states who judge this. Some of them have indeed been quite willing to accept the excuse [see here for a summary of some reactions]. However, the supporting states did not expressly say the attack was legal. They commonly expressed their understanding and support, which is quite different. From this point of view, I agree with Monica Hakimi that the strength of Article 2(4) is preserved. It could be a separate problem, however, if states accepted each other’s excuses too easily, as may well have been the case here. The end result could then indeed be what Anthea Roberts has cautioned against.

The main challenge is whether the separation of justifications and excuses can work in a decentralized legal system. But this is a problem of international law in general, not only in this specific context. In my view, the conceptual difference is still worth preserving in the international legal system. Keeping the Charter-mandated justifications and extra-Charter excuses separate would at least keep us paddling in the already-dangerous but probably-inevitable waters of ‘illegal but legitimate’. Any extra-Charter uses of force would thus remain doubtlessly illegal. As such, they could not be taken as evidence of state practice to claim a new customary exception to the prohibition of the use of force. Conflating justifications and excuses would mean that states might in the future completely drop the Charter language and invoke excuses to get out of illegality. This would then create a legal and policy framework for wider disobedience of the rules on the use of force and undermine the Charter rules. If Kosovo laid the foundation stone for ‘illegal but legitimate’, we need to be careful that Syria does not become the foundation stone for ‘legal because it is legitimate’.

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Alessandra Asteriti says

April 14, 2017

I completely agree on the conceptual distinction between justification and excuse (which I often use in my teaching) but it seems to me that, if peremptory norms, of which the prohibition of the use of force is certainly one, have to mean anything, is that derogations and excuses do not apply. Without going into a complex legal argument, just substitute 'genocide' for 'use of force' (two equally valid peremptory norms) and see if your argument still holds. Unless your argument is precisely that the prohibition of the use of force is not, or it should not be, jus cogens.

Rob Howse says

April 14, 2017

It is arguable that the customary law of "excuse" from responsibility (secondary obligations) is codified in Art. 25 of the ILC Articles on State Responsibility. So you would be saying that things have evolved from the state of the law reflected there? Interesting. Myself I hold that the Charter, when read in a sensible, evolutionary, teleological can accommodation a doctrine of justified humanitarian intervention. I think we are moving towards "legitimate" is "legal" and that's the kind of international law I like, not archaic formalism.

Adil Haque says

April 14, 2017

Hi Jure,

Question: If State A is not justified in attacking State B, but merely excused, does it follow that State B is justified in using force in self-defense against State A?

By way of analogy, if a person is unlawfully attacked by an excused actor (mentally ill, under duress, involuntarily intoxicated) then on many views that person is justified in using force in self-defense against that excused actor.

I suspect that things are not so simple, but I'm interested to hear your thoughts on the matter.

All the best,


Dapo Akande says

April 14, 2017

Hi Jure,

Thanks for the post! I would be grateful if, in responding to Adil's question, you could say a bit more about what work you think the distinction between justifications and excuses would do (or does do) in international law? What exactly, as a matter of law, would turn on whether a particular use of force is excused, as opposed to justified?

May I also ask a question which relates to Alessandra's comment, and picks up on something said by Rob in his comment as well. Do you think that international law already provides for excuses in (some of)the circumstances precluding wrongfulness in the law of state responsibility? If so, wouldn't it still be the case that one may not rely on an excuse in order to preclude the wrongfulness of what would otherwise be a breach of a norm of jus cogens?

Jordan Paust says

April 14, 2017

Adil: if State A IS justified, would not State B have a right of self-defense under 51 b/c it has been attacked?
In any event, R2P is part of the explanation before the SC and that is relevant to a textually attentive and policy-serving interpretation of Article 2(4).

Federica Paddeu says

April 14, 2017

Thanks Jure, for this most interesting post.

As you know, my forthcoming book (July 2017… if I manage to get the copy-edits back soon) is on justification and excuse in international law. So if you don’t mind, I’ll chip in a few remarks and give my thoughts on some of the questions posed.

As for the recognition in IL of excuses at present, well, the point is slightly difficult to address given that ‘excuse’ is a concept. There are not many general statements regarding the recognition of this notion. The better approach is to consider whether specific defences have been classified as excuses by states and whether tribunals have applied them as such. And the answer to the latter is no. A few (really a handful) of states have favoured a classification of necessity as an excuse, but on the whole states have treated it as a justification. This is indeed how Argentina and Zimbabwe pleaded it in investment arbitration, and how, in practice, most other states have asserted the defence. Additionally, the way it is currently drafted in ARS Article 25 reflects the logic of justification: as a lesser-evils. Lesser-evils is a consequentialist theory (an act-consequentialist theory, to be precise) of justification pursuant to which, essentially, whatever causes the lesser of two evils is lawful. Or, to put it in the opposite terms, whatever produces a net-benefit is lawful: since the act in necessity produces the lesser evil by preserving a superior interest, then it is lawful. Of course this will be difficult to assess, in particular where no scale of values exists (outside of peremptory rules). But that’s a separate matter. So, I disagree with Rob Howse that Article 25 (arguably) represents a theory of excuse. As it is currently formulated and as states have argued it, it is a justification. [Note that, I explain in the book, defences are not inherently justifications or excuses: they can be formulated either way, and why one formulation is preferred to another responds to a great number of considerations. A brilliant example of the reasoning involved in this choice is the Supreme Court of Canada’s decision in Perka v Queen which considered a plea of necessity and was tasked with determining whether it was a justification or an excuse. Necessity is in some legal systems a justification, in others an excuse, and in some, like Germany, there are two necessity defences: one a justification and the other an excuse. So state of necessity in IL could be reformulated as an excuse, as I explain in the book.]

Second, in respect of the availability of defences in respect of peremptory rules, well, Article 26 ARS (which was widely endorsed by States in the Sixth Committee of the GA) specifically states that no defences can be invoked as against peremptory rules. And this must hold whether they are justifications or excuses. I would argue that, while excuses may have a lesser impact on the normative pull of the rule, it remains the case that if an excuse is accepted as against a peremptory rule there will be a violation of one such rule that carries no legal consequences for the perpetrator. But recall that peremptory rules have consequences also for other states (ex art 41 ARS). What happens with these consequences? These states do not benefit from the excuse (excuses, after all, are personal). So are they still bound by them? It would be odd to reach the conclusion that the state who has violated a peremptory rule does not bear any consequences, but that other states nevertheless do. The ban on the availability of defences as against peremptory rules must include both justifications and excuses.

Finally, on the point raised by Adil of what the effect would be of a claim of excuse in these circumstances (whether it is an excuse of necessity or a specific excuse of humanitarian intervention), I think that it would be none at all. Excuses preclude responsibility which, according to the ARS, amounts to the obligations of cessation and reparation. But they do not exclude other possible legal consequences of wrongful acts. And wrongful acts have other consequences beyond those in the law of responsibility. Think, for example, of the invalidity of treaties as a result of a breach of the prohibition on the use of force. Or, likewise, the possibility to terminate or suspend a treaty as a result of material breach. Now these consequences are not included in the notion of responsibility and, as a result, they may not be precluded by the excuse. I would say that (and here I disagree with Roberto Ago as, in my interpretation, did the ILC in the second reading of the ARS) self-defence is a consequence of wrongfulness not encompassed by the notion of responsibility. As a result, an excuse cannot preclude the entitlement to act in self-defence should a wrongful use of force occur. And the consequence of this is that self-defence will be available as against the use of force of an excused actor. I accept that this argument depends on a conception of excuse which is concerned only with the exclusion of responsibility. But then, this is the only conception of excuse that states have so far considered (as this was the notion of excuse that the ILC considered in its work during the ARS).

I’ll conclude these very long remarks (for which I apologise!) with a historical detail: when in 1914 Germany invaded Belgium and Luxembourg, it pleaded necessity as an excuse. German Chancellor von Bethmann-Holleweg said: ‘Necessity knows no law. Our troops have occupied Luxembourg, and perhaps have already entered Belgian territory. Gentlemen, that is a breach of international law … We have been obliged to refuse to pay attention to the justifiable protests of Belgium and Luxembourg. The wrong – I speak openly – the wrong we are thereby committing we will try to make good as soon as our military aims have been attained. He who is menaced, as we are, and is fighting for his all can only consider how he is to hack his way through.’ (The translation is from L Zuckerman, The Rape of Belgium: The Untold Story of World War I (NYU Press, 2004), 11.)

Seeing where that led, I am not sure that – given that it is certainly not law at present – it is desirable for international law to develop to excuse uses of force beyond those expressly permitted (and therefore lawful) by the Charter.


Dapo Akande says

April 15, 2017


Thanks for that answer. It is very helpful. I look forward to seeing the book when it is out!

Kai Ambos says

April 14, 2017

Dear Jure
Thanks for bringing the justification / excuse distinction up, of course, a well known distinction in continental and comparative criminal law (recall the Eser/Fletcher MPI CrimL symposia starting in the 1980ies with Eser's seminal paper on the distinction as a key concept in the theory of crime). From this (crimL) perspective self-defence presupposes an unlawful act which means that a justified act/actor/attacker excludes a right to self-defence but not a merely excused actor/attacker.
For Adil's example this means that State B has indeed a right to self-defence if the attacking State A is not justified but only excused. But there are of course two (somewhat hidden) premises here: (I) the criminal law distinction between justification/excuse is sensible and (ii) it can be transferred to public international law and more specifically to the prohibition of the use of force vs justification discussion (I note in passing that for complicity we just saw in the mini symposium on Mile Jackson's complicity book that both areas - PIL and ICL - can well be treated together and inform / stimulate each other).
As to the premises above I think they are sound and at least no (i) already has an ICL precedent with the ICTY Erdemovic case (duress as valid defence for killing of innocents, Dudley v Stephenson etc, Cassese vs McDonald -> no justification, but possibly excuse). As to no (ii) Trump/Syria could become a precedent: if we follow the positivist reading of the Charter convincingly (but perhaps too hastily) defended by Marko there is clearly no justification stricto sensu for the Trump's/US's use of force but can he be blamed for having reacted out of moral outrage (of course, assuming that Assad was behind the chemical attack etc) ? This blame question/issue is exactly addressed by an excuse; in other words: we excuse an actor if we cannot/should not blame him (normatively speaking, in terms of a moral reproach) since, in a way, s/he did the (morally) right thing.
Of course, a plethora of other questions follow: is the actor's motivation or/and general moral attitude relevant? Does s/he has to act out of purely moral concern or could there also be other interests (domestic policy etc)? Do categories as blame, moral also apply to collective entities, espec. States (relevant for excuse re wrongful acts within the framework of state responsibility? I leave it here, sorry for the length, thanks to Jure for triggering this debate and the fellow commentators for taking it further ..

Kevin Jon Heller says

April 14, 2017

I doubt that describing Kosovo and similar acts as at best excused would satisfy the proponents of unilateral humanitarian intervention (UHI). As Rob's comment suggests, it seems clear that those who defend UHI feel that such actions are completely morally justifiable and thus should be legal despite Art. 2(4). The outcome might be the same regardless of whether a particular UHI is justified or excused (though I second Dapo's question above about what follows from the distinction), but the labelling still matters. An analogy might be to critical feminist legal scholars who insisted that battered women who killed be acquitted on the basis of self-defense, a justification, instead of on the basis of insanity, an excuse. The fact that both defenses led to acquittal was not enough, because the insanity route implied that battered women were crazy, not better able than a non-battered woman to perceive when they were in mortal danger.

Relatedly, I question the idea that the "illegal but legitimate...type of reasoning reflects the very logic of excuses." An excused act is never the right thing to under the circumstances, either legally or morally. It is simply an act that, because we understand that humans are fallible, we do not feel comfortable punishing. (A concession to human weakness, as many scholars and courts have put it.) So an excused act can never be legitimate in any strong sense of the word.

Hayder Al-Tamimi says

April 15, 2017

Let us agree at first on the definition of the following terms according to the jurisprudence of international law ; ( justification , excuse , legality , legitimacy) and also self-defence ,state of necessity .
Analogy from domestic legal jurisprudence for such terms may not be well applicable in all cases appeared within the framework of international law .

Jure Vidmar says

April 15, 2017

Thank you for all your comments. They are all excellent and very challenging. I will not pretend that I can answer all the issues you have raised, but I will try to focus on a few intersecting points: (i) are excuses included in the circumstances precluding wrongfulness under ARSIWA; (ii) if so, how does one get out of Article 26 (jus cogens); (iii) can excuses even be a public international law concept and what difference would that make in practice; and (iv) what are the systemic consequences of excuses in international law (e.g. for the right of self-defence).

I do believe that ‘circumstances precluding wrongfulness’ include some excuses and some justifications. I agree with Federica that in municipal legal systems necessity can be both excuse and justification. But I also think this is no different in international law. For example, necessity plays a role in the right to self-defence. What about necessity as a separate concept (Article 25 ARSIWA)? In my view, it is possible to conceptualize it as an excuse, even in the use of force context.

At this point, I need to outline a slightly broader use of force framework. As pointed out in the Commentary to Article 25 (para 5), the Caroline doctrine has always been a plea of necessity rather than self-defence. In my view, customary international law cannot set aside the Charter obligations. The formalistic reason is Article 103. Although it says that the Charter takes precedence over ‘obligations under any other international agreement’ this has been interpreted broadly to include custom as well. Article 103 therefore means that the Charter takes precedence over any other international legal obligations. Thus, if UN Charter prohibits the use of force, only UN Charter and no other source of international law can authorize any departures from this prohibition. In other words, only UN Charter can provide for justifications. There can thus be no anticipatory self-defence and no humanitarian intervention justification under customary international law.

What a valid plea of necessity could do is mitigate against responsibility for an illegal use of force. It is a difficult question when such a plea is valid. And this is where doctrines such as Caroline and humanitarian intervention may come into play. I agree with Federica that state practice does not readily prove that states invoke excuses rather than justifications. But at least when it comes to the use of force, after the Kosovo campaign even the intervening states were generally not advancing the Charter-mandated justifications, they were presenting their actions as the choice of a lesser evil and were essentially advancing excuses. It is somewhat similar now. The US did not advance any Charter-mandated justifications. It is true that states did not explicitly invoke necessity or even Article 25 ARSIWA directly. But mitigating circumstances for ‘illegal but legitimate’ uses of force have long been debated (see e.g. T Franck and N Rodely in response to Bangladesh, 67 AJIL 1973, p. 290). What I want to propose is that we start working on more conceptual clarity in this area of international law. Perhaps our theoretical work needs to catch up with state practice? And perhaps we are actually talking about general principles of law, and do not necessarily need to ground the concept of excuses in custom?

I agree that Article 26 is a problem, but would also like to add that ARSIWA are not a treaty and should not be read as such. The Caroline doctrine as necessity (see para 5 of the Commentary to ARSIWA) would then run into the same problem. When the use of force is debated as a peremptory norm, it also needs to be taken into consideration that unlike other peremptory norms, the prohibition of the use of force is not absolute. It is qualified with adjectives, such as ‘illegal’, or ‘aggressive’. This circumstance makes the use of force as a peremptory norm conceptually somewhat different than, e.g., torture, where we do not have ‘illegal torture’ as opposed to ‘legal torture’. While I agree that torture could not be excused as a plea of necessity, this may well be different with the use of force which has a qualified peremptory content.

The state against which force is being used retains the right to self-defence. For example, during the Kosovo campaign the Federal Republic of Yugoslavia (as it then was) had a valid right to self-defence, even if we were prepared to accept that the intervention was excusable on extra-legal grounds.

Finally, I do believe the conceptual difference is worth preserving in order to retain the strength of Article 2(4) and to deal with excuses on a case-by-case basis. Yet, some problems have been aptly spotted by the commentators and I am happy to acknowledge them. At the theoretical level, different legal systems conceptualize defences differently, so which model should be applied to international law? In my view, the state responsibility framework is a good point of departure. And I do agree with Hayder Al-Tamimi that we should work on a comprehensive jurisprudential foundations of international law. Borrowing from here and there does lead to systemic confusion.

Kriangsak Kittichaisaree says

April 16, 2017

The justification/excuse analogy in domestic criminal law or even international criminal law may not be appropriate in the context of jus ad bellum -- where any of the P5 of the UNSC has a veto power to shield itself and/or its allies from UNSC sanctions under Chapter VII of the UN Charter. Unlike domestic criminal law or ICL, the UN Charter does not treat all States as equal under jus ad bellum. One can only resort to preremptory norm to prevent and punish abuses of jus ad bellum. The big regret re the 7 April episode is that the US has not elaborated PIL justification(s) for its action which would have enlightened the ensuing PIL debate.

Anton Becker says

April 16, 2017

Best contribution of all times

Kriangsak Kittichaisaree says

April 17, 2017

An interesting development on the 7 April incident in Syria:
On 11 April 2017, Qatar informed Venezuela (Chair of the Coordinating Bureau of the Non-Aligned Movement) that Bahrain, Djibouti, Jordan, Kuwait, Morocco, Qatar, Saudi Arabia, UAE, and Yemen 'strongly oppose the issuance of [NAM's draft joint communique regarding "the aggression committed by the US against the Syrian Arab Rep. on Friday 7 April 2017"]'. Qatar et al 'strongly believe that the use of chemical weapons and all indiscriminate attacks against civilians constitute a flagrant violation to [sic.] international law, IHL and IHRL, and strongly believe that the International Community [sic.] must put an end to these violations and held [sic.] all responsible'. (Source: Note Verbale No. 2017/0027748/5 dated 11 April 2017).

Consequently, NAM could not achieve the necessary consensus on the draft joint communique mentioned above and, according to Venezuela, the draft 'is hereby dismissed'.