International Law: International Customary Law


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The Relationship between International Law and International Human Rights 

Does International Human Rights law exist as part of International law? What exactly constitutes international law? In attempting to answer these vital questions on the sources of international law, one could turn to the dicta of global tribunals for possible answers. For instance, in delivering its judgment, the Nuremberg Tribunal (1946) stated that:

‘the making of (its) charter was the exercise of the  sovereign legislative  power by the countries to which the German Reich unconditionally surrendered ….. the Charter is not an arbitrary exercise of power on the part of the victorious Nations …it is the expression of international law existing at the time of its creation; and to that extent is itself a contribution to international law.’ (Alston, p.124)

Academics such as Philip Alston argue that the Nuremberg tribunal and judgment , ‘applied international law doctrines and concepts to impose criminal punishment’ including the death sentence on 12 Nazi defendants for crimes under international law. (Alston, p.120). The defence of ‘nullum crimen sine lege, nulla, poena sine lege’ – there can be no punishment of crime without a pre- existing law- was rejected by the tribunal which invoked international law, specifically the General Treaty for the Renunciation of War of 27 August 1928 ( The Kellog Brian Pact), which was ‘binding on 63 nations, including Germany, Italy and Japan at the outbreak of war in 1939.( Alston p.124) .In other words, the signing of the 1928 pact led to a recognition among the nations that wars of aggression, such as the one undertaken by Nazi Germany, were a violation of international law.  What is particularly interesting about the Nuremberg Tribunal’s judgment is its recognition of international customary law adhered to by nation states as a source of international law; The Tribunal stated:

The law of war is to be found not only in treaties, but in the customs and practices of states which gradually obtained universal recognition , and from the general principles of justice applied by jurists and practiced by military courts.’ (Alston,  p.125) 


International Customary Law 

If International law on war, for instance, is to be found ‘not only in treaties’ as the Nuremberg Tribunal asserted, but also ‘in the customs and practices of states’, one must ask the question of how one identifies those customs which have crystallized into established practices of nation states, and have acquired the status of international law.

It would be helpful at this point to consider the Statute of the International Court of Justice (ICJ)  on the sources of International law.

Article 38, paragraph 1, of the the Statute of the ICJ identifies the sources of International law which this global court is required to apply when dealing with disputes submitted to it by Sovereign States. These sources are:

a. international conventions, whether general or particular, establishing rules expressly recognized by the contesting states;

b. international custom, as evidence of a general practice accepted as law;

c. the general principles of law recognized by civilized nations;

d. judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law. (ICJ 2018)

It appears that Article 38 recognizes International law to include not just international custom as general practice of nations which accept such custom as law, but also the general principles of law or opinio juris recognized by civilized nations.


How do customs and practices of States transpose into international  law?

The problem arises of determining when and how the customs and practices of Sovereign States on issues such as war, global and domestic security, treatment of foreign immigrants and the norms underpinning them coalesce into international law and become binding on and enforceable against nations.

Rosalyn Higgins, A former judge of the ICJ,  sheds some light on these vital issues in her essay: Problems and Process: International law and how we use it (1994)

‘If a customary rule loses its normative quality when it is widely ignored , over a significant period of time, does this not lead to a relativist view of the substantive content of international law, with disturbing implications? ….’


‘all states agree that international law prohibits genocide ( and that this total prohibition is today rooted in customary international law and not just in treaty obligations ).


So what if some states from time to time engage in genocide? How may we safely answer that genocide , while it sometimes occurs and while its very nature makes all norm compliance shocking, is certainly not the majority practice.


The customary law that prohibits genocide remains intact , not withstanding appalling examples of non-compliance’.

Higgins’ observations arguably reflect the social and political realities surrounding acts of genocide carried out by States such as Rwanda in the 1990’s and Myanmar in 2017. Myanmar, for instance, signed the Genocide Convention of 1948 on 30 December 1949, and ratified it in 1956, while Rwanda’s accession to the Convention was on 16 April !975.  (United Nations,  Treaty Seriesvol. 78, p. 277.) The impunity, however,  with which these States disregarded customary international law as well as the Genocide Convention 1948 that condemns the killing of members of an ethnical. racial , national or religious group was indeed shocking.

But the fact that the international community demanded or demands legal accountability for such atrocities through, for instance,  the medium of the International Criminal Tribunal for Rwanda and the International Criminal Court respectively, serves to remind us of the continuing existence of customary law recognized by nation States represented for instance in the United Nations Human Rights Council,  that condemns genocide as unlawful and morally reprehensible regardless of the indifference displayed by other States.

Does a Customary Rule of International law exist to prohibit the use of torture? 

Rosalyn Higgins argues that:

‘no one doubts there exists a norm prohibiting torture. No state denies the existence of such a norm ; and indeed it is widely recognized as a customary rule of international law by national courts.”


”But it is equally clear from, for example , the reports of Amnesty International , that the great majority of states systematically engage in torture. If one takes the view that non-compliance is relevant to the retention of normative quality, are we to conclude that there is not really any prohibition of torture under customary international law?


‘‘New norms require both practice and opinio juris before they can be said to represent customary international law. And so it is with the gradual death of existing norms and their replacement by others.’


The reason that the prohibition of torture continues to be a requirement of customary international law , even though widely abused, , is not because it has a normative status that allows us to ignore the abuse , but because opinion as to its normative status continues to exist.”


‘No state, not even a state that tortures , believes that the international law prohibition is undesirable and that it is not bound by its prohibition … existing norm does not die without the great majority of states engaging in both a contrary practice and withdrawing their opinion juris.” (Higgins, 1994).

Higgins’ comments on the norms underpinning the prohibition on torture are as relevant today as they were in 1994. The US Senate findings of the torture techniques such as waterboarding used by the CIA on detainees post 9/11 as well as the use of a torture site in Thailand purportedly supervised by the current CIA director, Gina Haspel, serves to remind us of the unspoken reliance on torture by western liberal democracies such as the US in furthering their policies on global and domestic security.

The recent findings of the UK Parliamentary Intelligence and Security Committee that the UK intelligence agencies including MI6  had been ‘complicit in hundreds of incidents of torture and rendition, mainly in partnership with the US in Iraq, Afghanistan and Guantanamo’ (The Guardian 2018) suggest that even liberal democracies known for their advocacy of human rights continue to engage in the very practices that their states denounce as inhumane. Such revelations of MI5 and MI6’s complicity in the use of torture and rendition carried out by the CIA were, however,  made public amidst denunciation of the use of torture and calls for an independent inquiry made by human rights groups such as Amnesty International  UK and Liberty. The UK government’s own recognition that such practices such as rendition is not acceptable is supported by Theresa May’s act of issuing a ‘a public apology to Abdel Hakim Belhaj who was kidnapped in 2004 with the assistance of MI6 and flown to one of Muammar Gaddafi’s prisons, along with his pregnant wife Fatima Boudchar.’ ( The Guardian 2018).

The practice of torture by the very States that continue to recognise the norms that prohibit torture presents us with a paradoxical state of affairs. Does International law in the form of International customary law practised and recognised by Sovereign States continue to exist in these circumstances?

If, as Rosalyn Higgins argues,  ‘‘new norms require both practice and opinio juris before they can be said to represent customary international law’, it may be submitted that States such as the UK and the US continue to recognise and state that they are bound by laws that prohibit the use of torture. As Anthea Roberts argues:

opinio juris concerns statements of belief rather than actual beliefs. Further, treaties and declarations represent opinio juris because they are statements about the legality of action, rather than examples of that action.’ ( Alston p.83).

Thus norms underpinning customary International law prohibiting State practices such as torture and genocide do not cease to exist just because States breach these norms so long as States continue to express their views on the illegality of such conduct. Might it be argued that such perspectives contribute to the indeterminacy of laws prohibiting  the use of State torture and genocide, and inevitably result in inadequate legal protection to the victims of such atrocities. The persistent denials by the Myanmar government of their complicity in the genocide of the Rohingya together with the increasing political support provided by China and Russia in the UN Security Council for the Myanmar military’s actions that have led to the atrocities against the Rohingya contribute to a form of international customary law that fails to provide adequate protection to ethnic minority groups against the brutal violence orchestrated by all powerful Sovereign States.

Martti Koskenniemi goes on to present an eloquent and cogent argument for recognising norms  ‘intended to safeguard basic human rights and fundamental freedoms’. He asserts:

It is inherently difficult to accept the notion that states are legally bound not to engage in Genocide, for example, only if they have ratified and not formally denounced the 1948 Genocide Convention.


Some norms seem so basic, so important, that it is more than slightly artificial that States are legally bound to comply with them simply because there exists and agreement between them to that effect, rather than because, in the words of the International Court of Justice (ICJ), non-compliance would ‘shock the conscience of mankind’ and be contrary to ‘elementary considerations of humanity.’ (Alston, p. 79).



‘Statute of the International Court of Justice’, ICJ, 2018.


Problems and Process: International Law and How We Use It. By Higgins Rosalyn. [Oxford: Clarendon Press. 1994]
‘Criticism mounts over UK’s post-9/11 role in torture and rendition’, The Guardian, 28 June 2018.



United Nations,  Treaty Seriesvol. 78, p. 277, 12 July  2018



International Human Rights by Philip Alston and Ryan Goodman, [Oxford University Press, 2012].



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