The Encyclopedia is a project of the Geneva Academy of International Humanitarian Law and Human Rights launched on 2 December 2013. The Enyclopedia aims to provide accurate, up-to-date information on weapons, the effects of their use, and their regulation under public international law, in a format that is accessible to non-specialists.+ Find out more
The prohibition of superfluous injury or unnecessary suffering leads to an apparent incongruity in international humanitarian law (IHL): while it would be generally lawful to kill a combatant, it is unlawful inevitably to inflict injuries or suffering beyond what is necessary to render them hors de combat.
Historically, the emergence of the concept of superfluous injury or unnecessary suffering marked the development of the first prohibitions and limitations on weapons that revolved around the protection of combatants. The first clear formulation of the logic underlying what is meant by ‘unnecessary’ suffering appears in the context of the prohibition of a specific weapon, namely Explosive Projectiles Under 400 Grammes Weight (‘exploding bullets’). The Preamble of the 1868 St Petersburg Declaration banning such ammunition articulated the rationale of the concept as follows:
[Considering] that the only legitimate object which states should endeavour to accomplish during war is to weaken the military forces of the enemy;
That for this purpose it is sufficient to disable the greatest possible number of men;
That this object would be exceeded by the employment of arms which uselessly aggravate the suffering of disabled men, or render their death inevitable;
That the employment of such arms would therefore be contrary to the laws of humanity …
This instrument proclaims three fundamental elements of the concept of unnecessary suffering. First, while formulated in relation to a particular weapon and towards the protection of combatants, this wording encapsulates one of the core pillars of IHL – that attacks must be limited to weakening (i.e. not annihilating) the forces of the enemy.
Second, needlessly aggravating the suffering or rendering death inevitable from wounds inflicted is contrary to the laws of humanity. This highlights the humanitarian and moral essence of IHL, i.e. protecting the human person to the extent not required by military necessity.
Third, and finally, the Preamble also outlines the fundamental difference between the rationales behind the protection of combatants on the one hand, and the protection of civilians on the other. Whereas civilians cannot be targeted at any time, combatants are lawful military targets and thus IHL does not prohibit their being intentionally killed. Accordingly, the preamble acknowledges that inflicting a certain degree of suffering on combatants is lawful under IHL and that the principle primarily protects combatants against certain effects of weapons. (It also acts to protect civilians when they directly participate in hostilities as they functionally lose their protection and can be targeted.)
The Hague Peace Conferences of 1899 and 1907 helped to shape the international normative framework for the regulation of weapons. Article 23(e) of the 1899 Hague Regulations concerning the Laws and Customs of War on Land (1899 Hague Regulations) states that it is 'especially' prohibited:
To employ arms, projectiles, or material of a nature to cause superfluous injury.
Article 35(2) of 1977 Additional Protocol I provides for a more elaborate formulation of this principle:
It is prohibited to employ weapons, projectiles and material and methods of warfare of a nature to cause superfluous injury or unnecessary suffering.
Thus, whereas the principle was developed only for means of warfare (i.e. the weapons), the provision in the 1977 Additional Protocol applies also to methods of warfare (i.e. the way a weapon is used). Furthermore, it confirms the wording ‘of a nature to cause’ in the 1899 text (instead of the expression ‘calculated to cause’ used in the 1907 Hague Regulations, arguably a mistranslation from the French original) and combines the wording of ‘superfluous injury’ as well as ‘unnecessary suffering’. These evolutions have significant implications with regard to the scope of this principle, as explained below.
The prohibition of superfluous injury or unnecessary suffering, together with the principle of distinction, have been recognized by the International Court of Justice (ICJ) as ‘cardinal principle(s) … constituting the fabric of humanitarian law’.ICJ, Legality of the threat or use of nuclear weapons, Advisory Opinion, 8 July 1996, §78. They form part of customary international law applicable to all parties to an armed conflict, whether international or non-international in character.This is the view of the International Committee of the Red Cross (ICRC).See Rule 85 of the 2005 ICRC Customary IHL Study.
While the prohibition on means or methods of warfare of a nature to cause superfluous injury or unnecessary suffering is accepted as custom, its practical definition and application are unsettled, in part due to inconsistent state practice. Indeed, this prohibition was once qualified by Antonio Cassese as ‘one of the most unclear and controversial rules of warfare’.A. Cassese, ‘Weapons causing unnecessary suffering: are they prohibited?’, Rivista di diritto internazionale, Vol. 58 (1975), p. 15. The ICJ defined unnecessary suffering as ‘harm greater than that unavoidable to achieve legitimate military objectives’.ICJ, Legality of the threat or use of nuclear weapons, Advisory Opinion, 8 July 1996, §238.
The prohibition, as codified in Article 35(2) of 1977 Additional Protocol I, focuses on the nature and/or extent of the effects of weapons, or the way they are used in terms of ‘injury or suffering’ caused. This notion is understood today as the equivalent of the French expression ‘maux superflus’ used in the French text of Additional Protocol, as well as in earlier instruments.The English text of the 1868 St. Petersburg Declaration used the word ‘suffering’, which remained in the 1907 Hague Regulations, whereas the 1899 Hague regulations referred to ‘superfluous injury’. The French words ‘maux superflus’ were used in the 1899 and 1907 Hague Regulations, as well as in 1977 Additional Protocol I allowing for a wider notion that included injury. The corresponding English translation makes use of both terms — injury and suffering — as the closest equivalent to the French word ‘maux’.
Three main criteria are commonly used to assess the level of suffering: the intensity of the pain, the degree of permanent disability, and the likelihood of death. Furthermore, suffering is considered the product of both physiological and psychological elements. Consequently, suffering can continue (for instance, in case of loss of a limb), even when the pain has gone. In the St. Petersburg Declaration, the term ‘suffering’ seemed to embrace the logic of excessiveness (needlessly aggravating the suffering of soldiers) and it remains a key component when considering the effects of a weapon, despite the fact that the term injury was seen as more quantifiable and objective. As noted by an expert, ‘[f]rom a military medical point of view the most obvious defect of the concept of “suffering” is that it cannot be numerically or graphically related to wounding.’See R. Scott, ‘Unnecessary Suffering? – A Medical View’, in M. A. Meyer (ed.), Armed Conflict and the New Law, British Institute of International and Comparative Law, London, 1989, p. 277. Several state military manuals refer to aggravation of an injury in this regard.See e.g. the revised version of the New Zealand Military Manual. State practice now widely recognizes both physical and psychological suffering as well as injury as constituting key components of the application of the rule. For example, it is recognized that ‘the rule does prohibit deliberate design or alteration of a weapon solely for the purpose of increasing the suffering of those against whom it is used.’W. H. Parks, ‘Memorandum of law: The Use of lasers as Antipersonnel Weapons’, 29 September 1988, in The Army Lawyer, November 1988, p. 3. Similarly, while, to date, no case has addressed only the psychological harm inflicted by a weapon, the relevance of that aspect has not been dismissed in the practice of states.
Strictly speaking, the terms could be taken not to cover death per se. The Preamble of the 1868 St. Petersburg Declaration prohibited two effects: ‘aggravating suffering’ and ‘rendering death inevitable’. The reference to the latter notion disappeared in subsequent IHL instruments. It is not certain whether the prohibition of weapons rendering death inevitable is separate from the rule prohibiting superfluous injury or unnecessary suffering. This was a point of contention in the Advisory Opinion on the legality of nuclear weapons by the International Court of Justice. State practice tends to consider death as an effect of weapons within the scope of the general prohibition of superfluous injury or unnecessary suffering rather than an autonomous rule, despite the restrictive literal meaning of injury and suffering. But, as explained above, the principle of superfluous injury or unnecessary suffering cannot be reduced to the question of the likelihood (or even certainty) of death. This also begs the question of whether the evolution of medical science would allow certain weapons’ effects to be lawful today, whereas in earlier decades those effects would have inexorably led to death and thus to the weapon being deemed to cause unnecessary suffering.
Finally, a question arose as to whether the broad notion of ‘maux’ can cover material damage. Strictly speaking, the St Petersburg Declaration was deemed to protect the quality of a human being, excluding the idea of material damage from the scope of the principle. However, several cases can be found in state practice interpreting the principle to prohibit excessive material destruction,See e.g. Australia, Defence Force Manual, 1994; USA, Air Force Pamphlet 110-31, 1976; and Operational Law Handbook, JA 422, International and Operational Law Department, The Judge Advocate General’s School, 2003. although this may be the result of conflation with the notion of military necessity.
The second issue in defining this principle is the type of causal link required between the relevant effects and the weapon, or in other words which effects must be considered when reviewing the legality of a means of warfare. The development of the prohibition on superfluous injury or unnecessary suffering gave rise to another difference of translation: the English expression ‘calculated to cause’ was used in the 1907 Hague Regulations and is still used in certain declarations by states. This expression could restrict the scope of the prohibition as it implies that the weapon needs to be designed and/or intended to cause such effects. The broader and more objective term based on the expression ‘weapons of a nature to cause’, as used in Article 35(2) in 1977 Additional Protocol I, is now commonly accepted.
The question remains to determine what the reference to the ‘nature’ of a weapon means. Specific regulations on weapons, such as Protocol I on non-detectable fragments annexed to the 1980 Convention on Certain Conventional Weapons, used the criterion of the ‘primary effect’, i.e. the main effect the weapon was designed to produce and which results from its use. This is also referred as the ‘design purpose’ approach as opposed to an ‘effects-based’ approach.Another example is Art. 1 of Protocol IV to the CCW which prohibits ‘to employ laser weapons specifically designed, as their sole combat function or as one of their combat functions, to cause permanent blindness to unenhanced vision’. The latter would primarily consider effects that typically result from the use of a weapon in practice, with less regard to the presumed intention of the designer or user.The difference between these approaches to weapons regulation is reflected in the definition of a cluster munition in Art. 2(2) of the 2008 Convention on Cluster Munitions, albeit not with respect to the rule on superfluous injury and unnecessary suffering. Art. 2(2)(a) refers to ‘a conventional munition that is designed to disperse or release explosive submunition…’, [emphasis added] whereas sub-paragraph (c) refers to ‘indiscriminate area effects’ that are to be avoided (irrespective of whether these are intentional or not). Some states define the ‘nature’ of a weapon by reference to the normal and foreseeable use of a weapon. However, since the prohibition extends to ‘methods of warfare’, the principle can prohibit use of a weapon in a certain manner (i.e. a method that is of a nature to cause superfluous injury or unnecessary suffering), despite the weapon not being prohibited in all circumstances.
Ultimately, the issue of effects is closely related to the benchmarks or criteria used to assess injuries or suffering in order to determine whether they are superfluous or unnecessary. Two main ways have been used to interpret the standard of reference for such assessment. The first, sometimes called the ‘humanitarian’ or ‘medical’ interpretation, is founded on the nature and/or the level of the effects of the weapon. It would imply the existence of a threshold beyond which any weapon, whatever its military utility, causes unnecessary effects. The SIrUS Project initiated by the International Committee of the Red Cross (ICRC) was partly based on this approach, albeit on the basis of a slightly different methodology. It focused on describing the effects of commonly used conventional weapons with a view to gathering data. After having identified a set of the main effects of conventional weapons, such as the mortality rate, the SIrUS Project used the findings to conclude that weapons that produced effects in excess of those commonly observed in relation to conventional weapons were of a nature to cause superfluous injury or unnecessary suffering. This approach was, though, criticized for not having taken into account the military side.
The second interpretation lies in a comparison between the effects of the weapon and its military utility. The greater the military utility of a weapon, the easier it would seem to justify the injury and the suffering it inflicts. In that context, the distinction between anti-personnel and anti-materiel weapons plays an important role in framing its interpretation and clarifying its content. Further, the evolution of the military utility of a weapon may change the result of the equation, even in cases considered manifest at the time of the prohibition. When explosive bullets of less than 400 grammes turned out to be efficient against aircraft, they became anti-materiel weapons. Their effects could no longer be solely assessed under the criterion of putting someone hors de combat. State practice consequently restricted the scope of the rule to antipersonnel use.
From the St. Petersburg Declaration onwards, the legal benchmark has been to assess what is necessary to ‘disable’ a soldier or put him hors de combat. 1977 Additional Protocol I defines the term hors de combat as follows: ‘a person is hors de combat if he has been rendered unconscious or is otherwise incapacitated by wounds or sickness, and therefore is incapable of defending himself’.See Art. 41(2)(c), 1977 Additional Protocol I. Explosive bullets under 400 grammes in weight in 1868 and expanding bullets in 1899 have been deemed to cause more harm than necessary to achieve this ‘individual’ goal of putting soldiers hors de combat. The situation is more complicated when one changes the scale or the context. Weapons can be used against troops instead of individual soldiers, and can cause greater harm than necessary to put one soldier hors de combat. Additionally, weapons used to cause material damage can often cause more harm to individual soldiers than would be necessary to put them hors de combat. In this case, the military utility would presumably shift from killing soldiers to neutralizing enemy arsenal or infrastructure.
As noted above, although the concept of superfluous injury or unnecessary suffering emerged as a legal principle in treaty law, it has now acquired the status of customary international law and is binding on all parties to armed conflict, including those states that are not parties to 1977 Additional Protocol I. The ICRC 2005 Customary IHL Study concluded that the customary norm covers both means and methods of warfare. It documents extensive state practice acknowledging the customary nature of this principle beside the customary status of prohibitions of specific weapons. The International Criminal Tribunal for the former Yugoslavia (ICTY) has confirmed the view that the principle applies not only in international but also in non-international armed conflicts.See ICTY, Prosecutor v. Tadić, Decision on the defence motion for interlocutory appeal on jurisdiction (Case No. IT-94-1), 2 October 1995, §127.
IHL contains a series of prohibitions and limitations on the use of specific weapons. Certain weapons are prohibited in all circumstances due to their characteristics while others are only governed by restrictions on use. The ICRC 2005 Customary IHL Study quoted the following weapons cited in state practice as causing unnecessary suffering ‘if used in certain or all contexts’:
It stressed though that there is ‘insufficient consensus concerning all of these examples to conclude that, under customary international law, they all violate the rule prohibiting unnecessary suffering’.ICRC 2005 Customary IHL Study, pp. 243–4. Only some of those weapons, mostly of antipersonnel use, could be considered as stemming clearly from the principle.
The terms ‘methods of warfare’ include a broad array of rules depending on the definition retained. Commonly, ‘methods’ designate the way or manner weapons are used. However, the concept of method of warfare also comprises any specific ways of conducting hostilities, whether in a tactical or strategic manner (and not necessarily specifically related to weapons), to outweigh and weaken the adversary, such as bombing, as well as specific tactics used for attack, such as high-altitude bombing. In that regard, certain prohibited methods relate to the protection of combatants, notably the prohibition ‘to kill or wound treacherously individuals belonging to the hostile nation or army’See Art. 23(b), 1907 Hague Regulations. or ‘to declare that no quarter will be given’.Art. 23(d), 1907 Hague Regulations.
While state practice provides few specific examples of methods that would be prohibited under this principle, using incendiary weapons for antipersonnel purposes could in certain circumstances be considered unlawful. Rule 85 of the ICRC 2005 Customary IHL Study reads: ‘The anti-personnel use of incendiary weapons is prohibited, unless it is not feasible to use a less harmful weapon to render a person hors de combat.’ Conversely the use of such weapons to neutralize military equipment would not be a prohibited method.
It is uncontested that the principle has significant legal bearing when a state assesses the legality of a weapon, and as a fundamental principle of IHL it plays a key role in framing the development of new weapons. It is, however, true that, to date, its concrete application has proved to be effective mostly in regulating means of warfare that have inflicted manifestly excessive suffering and injury in the context of strictly anti-personnel use. Given the complexity of the notion of the military utility of a weapon, it is perhaps not surprising that most treaties prohibiting or limiting the use of specific means of warfare cover anti-personnel weapons with an individual purpose. In such a case, it is far easier to reach agreement on the application of the test balancing both elements.
Last updated on: 30 November 2013