Chapter 4 shows that military necessity can affect the legitimacy of a belligerent act where the act is deemed evil and its purpose is considered legitimate. In no other circumstances, however, does an act’s legitimacy depend on whether it is materially necessary. As far as IHL norm-creation is concerned, the lack of material military necessity per se is never a reason for a belligerent act’s illegitimacy. If a warring party encumbers itself with missed opportunities and mounting blunders, it has only itself to blame. Nevertheless, in some circumstances, IHL does delegitimise exclusively self-inflicted evil, and it does mandate action with a view to reducing such evil.

This introductory chapter raises two questions that will guide us through the book. First, what does it mean to say that IHL ‘accounts for’ military necessity? Second, to what normative consequences does IHL accounting for military necessity give rise? The chapter offers the reader a mental roadmap of the discussions ahead. It also highlights the various tenets of inclusive legal positivism upon which the subsequent chapters are built.

Chapter 3 addresses three major objections against the idea that we can consider military necessity exclusively in its material sense. First, by assessing an act’s material necessity or non-necessity, one may already be passing judgement on its quality as something desirable or undesirable, what a competent soldier should or should not do. Second, pursuing military necessities and avoiding non-necessities may mark not only a belligerent’s competence qua member of an occupational group, but also a person’s competence qua moral agent. Third, it is arguable that soldiers should refuse to deem unethical acts militarily necessary, all things considered. Consequently, only ethically competent fighting should count as truly vocationally competent fighting.

Chapter 9 delves into juridical military necessity as an exception. It begins by distinguishing juridical military necessity from the state of necessity, a circumstance precluding the wrongfulness of an act under the international law of state responsibility, on account of their distinct normative status and distinct contents. The discussion then proceeds to the four cumulative requirements customary IHL imposes when invoking express military necessity clauses. First, the measure must be taken as primary for some specific military purpose. Second, the measure must be ‘required’ for the purpose’s attainment. This requirement may be sub-divided into three components, namely relevance, minimum injury and proportionality. Third, the purpose must itself conform to IHL. Fourth, the measure must also conform to IHL.

Chapter 8 deals with exclusion. The inevitable conflict thesis errs when it asserts that all positive IHL rules, including those that are unqualified, involve military necessity and humanity in their norm-creation. This chapter shows, rather, that IHL norm-creation does not always involve the military necessity–humanity interplay. Ill-advisedly, the inevitable conflict thesis also holds that neither military necessity nor humanity may be invoked in defence of deviations from unqualified IHL rules. While Kriegsräson and its variations are properly excluded, humanitarian imperatives may justify non-compliance with IHL and/or render technical compliance unlawful.

Chapter 6 revises two of the shortcomings from which the inevitable conflict thesis suffers. First, the inevitable conflict thesis claims that military necessity and humanity in their material context never coincide. On the contrary, there are numerous instances where a belligerent act is both humane and necessary, or both inhumane and unnecessary, as the case may be. Second, according to the inevitable conflict thesis, both military necessity and humanity generate imperatives. For the purposes of IHL norm-creation, however, there is simply no reason why materially necessary acts should be performed, or why materially unnecessary ones should be avoided. This shows that military necessity is normatively indifferent. Although humanity generates imperatives in many cases, it also remains indifferent in others.

Chapter 2 illustrates how material necessity reflects a two-fold truism that it is in each belligerent’s strategic interest to do what is necessary and to avoid what is unnecessary. The notion evaluates how the means taken advances the ends sought under the prevailing circumstances. A given act can be a military necessity compared to some alternatives, yet a non-necessity compared to some other alternatives. Acts that are wasteful, excessive, inapposite, futile or purposeless are improvable military non-necessities rather than solely the results of war’s irresistible friction. The necessity assessment of particular action cannot be meaningfully generalised or seen outside of its factual context.

Chapter 7 demonstrates that, contra the inevitable conflict thesis, military necessity never affirmatively conflicts with humanity. Where humanity demands what military necessity permits, or where humanity condemns what military necessity merely tolerates, the belligerent always satisfies both considerations by acting as directed by humanity. IHL framers are more likely to impose unqualified prohibitions against acts deemed inhumane and unnecessary than to make humane and necessary acts obligatory. Military necessity’s normative indifference also means that, even where humanity demands unnecessary acts or condemns necessary acts, the belligerent still satisfies them jointly by acting as directed by humanity. IHL framers are then to decide whether to obligate jointly satisfactory behaviour and, if so, whether to obligate it unqualifiedly, principally, indeterminately or exceptionally.

Chapter 11 recapitulates this book’s principal findings. It also highlights their relevance vis-à-vis jus ad bellum, international human rights law and international criminal law.