Military Necessity

Led by Nobuo Hayashi
Mar 2008 - Oct 2012


First installment - "Requirements of Military Necessity in International Humanitarian Law and International Criminal Law" - published in Boston University International Law Journal [Vol. 28:39 2010]. 

Second installment - "Contextualising Military Necessity" - accepted for publication in Emory International Law Review [Vol. 27 2013].

Third installment - "Military Necessity as Normative Indifference" - published in Georgetown Journal of International Law [Vol. 44 2013].

At the very heart of this Ph.D. project is an effort to elucidate military necessity. Previous scholarship on this matter has been severely hindered by contextual cross-speech, unreflected assumptions, logical equivocations and the like. Through his writings, the author fundamentally challenges the idea that belligerent conduct’s lack of military necessity per se is or signifies a reason for its illegitimacy or unlawfulness under international humanitarian law (IHL). Quite on the contrary, as far this law is concerned, nothing in military necessity normatively restricts. In its strictly material context, military necessity merely embodies a two-fold truism. Thus, it is in one’s strictly strategic self-interest to pursue necessities of war and avoid non-necessities of war; conversely, it is against one’s strictly strategic self-interest to let go of necessities of war and/or encumber oneself with non-necessities of war. In this context, it is, ultimately, all a matter of fighting competently or incompetently. Accordingly, if, for example, one imperils oneself with the dispiriting prospect of defeat by chasing non-necessities through blunders, one only has oneself to blame. In the context of IHL norm-creation, military necessity embodies normative indifference. On the one hand, it merely, if robustly, permits the pursuit of material military necessities and the avoidance of material military non-necessities; but it never really makes them mandatory. Nor, on the other hand, does normative military necessity deplore or condemn belligerents for forfeiting success or inviting failure by missing necessities and going after non-necessities; rather, it also permits, albeit moderately, even these infelicities. The mere fact that it is materially unnecessary to do this, or to fail to do that, itself gives the framers of IHL rules no cause to forbid or restrict the doing of this or the failure to do that. Juridically, military necessity embodies an exception, neither a justification nor excuse. Military necessity clauses found in certain provisions of positive international humanitarian law exceptionally authorise behaviour deviant from the latter’s principal prescriptions if and to the extent such behaviour satisfies specific requirements. If not, or no longer, in satisfaction of these requirements, the conduct in question simply reverts to being governed by the principal rule, of which it now becomes an unexcepted instance. The conduct’s unlawfulness arises from its breach of the principal rule, not its lack of military necessity or the now inoperative exceptional clause.

The author does confirm the already widely accepted fallacy of Kriegsräson. In a nutshell, Kriegsräson asserts that the material military necessity of a given belligerent act alone somehow “rights” or “repairs” its unlawfulness otherwise conclusively established by those validly posited IHL rules applicable to it. Nevertheless, past attempts at explaining its fallacy have produced highly counterintuitive consequences. The author tackles two of them. One is what may be called, somewhat provocatively perhaps, “counter-Kriegsräson.” On this view, a belligerent act’s mere lack of material military necessity somehow “wrongs” or “vitiates” its lawfulness otherwise conclusively kept intact by the relevant rules of positive international humanitarian law. The author refutes counter-Kriegsräson because, first of all, no considerations of military necessity in fact survive the process of IHL norm-creation, with the result that no military necessity residue operates as an additional layer of normative regulation on belligerent conduct over and above that emanating from validly posited IHL rules. (N.B.: Kriegsräson is untenable mutatis mutandis for the same reason.) In addition, even if counter-Kriegsräson were valid, it would be devoid of any prohibitive or restrictive content since military necessity is normatively indifferent in the sense described above. The other counterintuitive consequence involves the notion that validly posited IHL rules creating unqualified obligations exclude not only military necessity pleas de novo but also humanity pleas de novo. Refuting this position – let us call it the “inevitable conflict” thesis of military necessity – requires discussions that are a little more complex. In a nutshell, this thesis is predicated on the notion that military necessity and humanity are “diametrically opposed” considerations, that they are inevitably in conflict with each other, and that their “dialectical compromise” struck in the form of unqualified IHL rules being validly posited by their framers means that neither military necessity nor humanity pleas de novo are admissible vis-à-vis such rules. The author’s objections are three-fold. First, military necessity and humanity do, in fact, often align with each other. Second, since military necessity is normatively indifferent, it never generates imperatives and, as such, never affirmatively conflicts with any such imperative as may emanate from humanitarian exhortations or demands. On the contrary, where both humanitarian exhortations or demands and military necessity's indifferent permissions are at stake, one always jointly satisfies them by acting in accordance with the former (hence a "joint satisfaction" thesis of military necessity). Third, and, most controversially, the process of IHL norm-creation cannot be said so readily to have “accounted for” those bits of humanitarian considerations that are normatively non-indifferent. The author argues that unqualified IHL rules exclude military necessity pleas de novo (a) because such rules extinguish all contrary liberties robustly or moderately permitted by indifference considerations not to act as unqualifiedly obligated by the rules, and (b) because military necessity is a species of indifference considerations. Conversely, where an unqualified rule of positive international humanitarian law obligates given behaviour yet humanity non-indifferently exhorts or demands contrary behaviour, and where the rule’s addressee acts as demanded by the latter, it is not inconceivable that the addressee may admissibly plead humanity de novo in defence of his or her action vis-à-vis the rule.

Also, although peripherally for the author’s immediate purposes, the particular manner in which he discusses the role military necessity plays in the process of IHL norm-creation opens up room for further thought regarding closely associated IHL precepts such as humanity, chivalry, honour and fairness. One corollary arising from his thesis is that humanity contains both considerations which are normatively indifferent and those which are normatively non-indifferent. Similarly, chivalry, honour and fairness may, at least in part, be seen as species of non-indifference considerations. The various modes of their involvement in the process of IHL norm-creation, as well as the interesting consequences they produce, may merit further investigation. For instance, while Kriegsräson is rejected (as it should clearly be), a Humanitätsräson of a normatively non-indifferent kind – i.e., that acting as exhorted or demanded by humanity “rights” or “repairs” the act’s unlawfulness otherwise unqualifiedly established by validly posited IHL rules – might not be so easily dismissed. Nor, for that matter, might even a non-indifferent “counter-Humanitäsräson” – i.e., that failing to act as exhorted or demanded by humanity “wrongs” or “vitiates” the failure’s lawfulness otherwise unqualifiedly kept intact by validly posited IHL rules – be too far-fetched. In view of its potentially controversial ramifications, the very idea that non-indifference considerations may survive the process of IHL norm-creation calls for further careful scrutiny.

This Ph.D. project at PRIO is funded by the Norwegian Ministry of Defense.

PRIO Supervisor: Greg Reichberg

Research Groups


Peer-reviewed Journal Article

Hayashi, Nobuo (2010) Requirements of Military Necessity in International Humanitarian Law and International Criminal Law, Boston University International Law Journal 28(1): 39–140.
Hayashi, Nobuo (2006) The Role of Judges in Identifying the Status of Combatants, Acta Societatis Martensis 2: 69–92.

Book Chapter

Hayashi, Nobuo (2010) Continuous Attack Liability without Right or Fact of Direct Participation in Hostilities – The ICRC Interpretive Guidance and Perils of a Pseudo-Status, in Joanna Nowakowska-Malusecka, ed., International Humanitarian Law – Antecedences and Challenges of the Present Time. Bydgoszcz, Poland: Branta: Oficyna wydawnicza (56–78).
Hayashi, Nobuo (2010) Continuous Attack Liability Without Right or Fact of Direct Participation in Hostilities – The ICRC Interpretative Guidance and Perils of a Pseudo-Status, in Joanna Nowakowska-Malusecka, ed., Międzynarodowe prawo humanitarne. Poland: Wydawnictwo Wyższej Szkoły Oficerskiej Sił Powietrznych (56–79).

Edited Volume

Hayashi, Nobuo (ed.) (2000) Multilateral Treaty-Making - The Current Status of Challenges to and Reforms Needed in the International Legislative Process. Leiden: Brill.

Non-refereed Journal Article

Hayashi, Nobuo (2013) Military Necessity as Normative Indifference, Georgetown Journal of International Law 44(2): 675–782.

Book Review

Hayashi, Nobuo (2009) Review of Eve La Haye, ed., War Crimes in Internal Armed Conflicts, in Nordic Journal of Human Rights 27(3): 357–365.