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Standardizing Standards of Proof in International Law

Article by Ashna Devaprasad,

With an increasing number of technical and scientific cases confronting international law, there has never been a more opportune moment for courts to clear the air on the present ambiguity surrounding the use of evidentiary standards. Over the years, international courts seem to have favored a malleable approach, wherein adjudicators play an inquisitorial role and exercise the freedom to determine evidentiary standards, on a case-by-case basis. Such practices have resulted in the enunciation of varying and flexible standards of proof, including but not limited to “beyond a reasonable doubt,” “clear and convincing,” “conclusive evidence,” “with a high degree of probability,” “balance of probabilities,” “sufficient certainty,” “reasonable basis to proceed,” “reasonable grounds,” and the “prima facie” standard.

The question of vastly varying standards of proof has been a topic of debate among academics and scholars. Courts, however, have evaded this discussion and resorted to obfuscation. This article seeks to contextualize the arguments put forth in support of objective and flexible standards of proof, in order to understand how courts can apply consistent and fair standards of proof under international law, particularly in cases involving scientific and technical questions.

Are Objective Standards of Proof Preferable?

The term standard of proof refers to the quantum of evidence necessary to substantiate parties’ factual claims. Parties are expected to meet this threshold of proof to convince adjudicators about their claims’ rationality and genuineness. Proponents of objective standards of proof draw strength from the claim that such standards ensure transparency and an element of standardization in judicial decisions. They argue that such standards help parties strategize their cases and leave less room for highly subjective judicial instincts.

For instance, when there is an armed attack against a state, the state cannot act in self-defense until it has exhausted all other peaceful options. This right to self-defense is only available to a state if it satisfies the two-pronged test of necessity and proportionality, as recognized under customary international law and reaffirmed by the International Court of Justice (ICJ) in its 1986 judgment in Nicaragua v. USA (Case Concerning Military and Paramilitary Activities in and against Nicaragua). In order to satisfy the conditions of necessity and proportionality, a state must justify that the use of force was necessary to achieve legitimate ends of self-defense and that the level of force used was proportionate to the armed attack or was the least drastic measure. Thus, necessity means an ‘absence of reasonable alternatives’ while proportionality involves assessing the means used by comparing the injury expected from the attack to the consequences produced by the act of self-defense as a whole.

Today, the standard of proof required to establish the occurrence of an armed attack, thereby necessitating self-defense, remains unclear. In her separate opinion in Islamic Republic of Iran v. United States of America (Oil Platforms), Judge Rosalyn Higgins of the ICJ criticized the Court’s approach in United Kingdom of Great Britain and Northern Ireland v. Albania (Corfu Channel) and Nicaragua v. United States. There, the Court merely rejected evidence as “insufficient” and did not clearly articulate what standards of proof are required in each case to establish the existence of an armed attack. The DRC v. Uganda decision was another missed opportunity for the ICJ to clarify the level of credibility called for to justify claims relating to the occurrence of an armed attack. To further complicate the matter, the Court contradicted the standard that was developed in preceding jurisprudence. Likewise, the WTO Panel in its report in United States, Appellant v. India, Malaysia, etc., Appellees (United States - Import Prohibition of Certain Shrimp and Shrimp Products) informed the parties that they may have reached conclusions regarding a particular claim based on the “sufficiency” of evidence, without clarifying the level of proof necessary.

The inconsistent application of standards of proof in a similar factual matrix can discourage states from approaching international courts. In recent instances, states have taken the liberty to formulate their own standards of proof. For example, the Attorney Generals of the United States, United Kingdom, and Australia made statements concluding that there must be a “reasonable and objective basis” for determining whether or not an armed attack is imminent. Similarly, by coining innovative phraseology such as “non-military pre-emptive action” as India did in the Balakot airstrikes, states are twisting the ambiguity in their favor. The result is a hybridized and highly contested manifestations of preventive and anticipatory self-defense, partially attributable to the unclear evidentiary standards on the subject.

In Defense of Flexible Standards of Proof

Those who defend the application of flexible standards of proof espouse the idea of giving courts the freedom to prudently balance evidentiary standards while appraising facts on a case-specific basis. However, while doing so, courts must tread with caution. For example, while placing reliance on the reports of the United Nations the Independent International Fact-Finding Mission on Myanmar (IIFFMM) in the The Gambia v. Myanmar (Rohingya Genocide case), judges must account for the less formal, idiosyncratic standards of proof that may be used by fact-finding missions while collecting and evaluating information that may later be produced as factual evidence in court. There are also concerns about a lack of transparency, erroneous information and inadequate scrutiny of evidence while relying on such organizations.

Imposing excessively high and precise standards of proof on parties may also have negative consequences such as not having access to quality evidence, particularly in cases involving charges of exceptional gravity. The use of such standards may lead to parties being unable to meet the evidentiary demands of courts, thereby running the risk of exonerating potential human rights violators. As noted by Judge Cançado Trindade of the ICJ, demanding entirely conclusive standards of proof in cases of genocide that necessitate proving specific intent (dolus specialis) can also be counterproductive to implementing the Genocide Convention. Rather, allowing adjudicators to use discretion while appreciating evidence enables them to maintain fairness between parties while analyzing their burden of proof.

Finding Middle Ground

The exercise of determining standards of proof is critical to arriving at fair conclusions, but invariably entails an element of uncertainty. To appreciate some degree of uncertainty, parties must first acknowledge the differing evidentiary frameworks within which domestic and international adjudicatory forums operate. While domestic judicial pronouncements are generally replete with uniform procedures and standards, international adjudicators deal with parties from divergent cultural and legal backgrounds, which makes defining, interpreting and applying standards of proof all the more cumbersome. Unlike domestic courts that are equipped with the support of law enforcement agencies, international courts face jurisdictional limitations vis-à-vis conducting independent evidence collection exercises and coordinating with domestic authorities.

Moving forward, disputes that come before international courts are likely to involve scientific and data-driven questions of evidence. In cases that call for implementing a treaty or convention, the standard of proof must align with a teleological interpretation of its provisions. For instance, in the case of Australia v. Japan (Whaling in the Antarctic), the ICJ extensively examined advanced scientific data on whaling practices, both from the International Whaling Commission (IWC) and scientific experts. The court’s decision to end Japan’s whaling program was based on a standard of “objective reasonableness” where parties are held up to the “reasonable” standard of proof but with the rigor of the “necessity” test. This decision was also in line with the objectives of the International Convention for the Regulation of Whaling (ICRW), which aims to sustainably protect threatened species of whales from overhunting by devising a system of whale stocks, non-lethal hunting practices, and strict moratoria. Upon concluding that the use of lethal methods to kill whales was not strictly necessary for Japan’s research, the court devised a standard of proof that balanced the parties’ relative rights and required Japan to explain the reasonableness of different aspects of its Whaling program.

Professor Charles Weiss of Georgetown University formulated a rule to pragmatically identify standards of proof in cases that involve the analyses of scientific evidence. Weiss’s method uses a scale of legal standards that are hierarchically arranged, with each standard of proof made equivalent to assigned degrees of scientific certainty required in different legal situations. The rule aims to help judges match standards of proof with the level of scientific certainty necessary to analyze the repercussions of a given action. Although this method is not fool-proof, it can aid judicial decision-makers in pinpointing a more precise standard and accounting for its application to the unique facts in each case. A redesigned formulation of this rule may be used in other cases of complex evidence as well.

Concluding Thoughts

International courts often rely on evidence collected by commissions of inquiry consisting of members from various political, legal, and socio-cultural backgrounds. These commissions carry out investigations in diverse regional environments and analyze evidentiary questions from unique socio-political perspectives. They define and apply standards of proof in a less systematized manner than courts. Although these commissions are required to clearly explain the standards of proof adopted, there have been instances where no standards are articulated or where the application of standards is incongruous with that in international courts. Hence, courts must ensure a higher degree of interoperability between the theoretical and practical variations in the evidentiary practices employed by judicial and non-judicial bodies. The appointment of groups of experts to guide courts on how to weigh evidence, interpret fact-finding reports, and coordinate between the parties to establish improved negotiations and fact narratives concerning methods of proof can also help streamline the process. Rather than getting bogged down by arguments surrounding the use of hypertechnical language to distinguish between standards of proof, courts must use standards that broadly satisfy the umbrella test of objective reasonableness to ensure fairness between the parties. Before a court accepts or rejects an evidentiary claim, it must first provide cogent factual and legal justifications for doing so. Such an exercise involves actively engaging in counter-arguments with parties on the implications of using such a standard in a given case. Otherwise, much like courts, states will shy away from responsibility and steer clear of seeking international adjudication.


Ashna Devaprasad is a penultimate year student at the National University of Advanced Legal Studies, Kochi, India with a keen interest in criminal law and international environmental law.



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