Editor’s note: this webpage is the text of a portion of “Quantum of Silence: Inaction and Jus ad Bellum,” by Dustin A. Lewis, Naz K. Modirzadeh, and Gabriella Blum, HLS PILAC, 2019. A link to the PDF version of this part is available here, and a link to the full paper and annex is available here.
I. Introduction
States frequently take actions and make statements that implicate international law. But because States do not — and, indeed, could not — express a view on each such act or statement by all other States at all times, silence seems to be the norm, rather than the exception, in international relations.
When States and other international actors do not express their views on a particular incident, issue, or statement that implicates international law, what is the legal significance, if any, of their silence? Does it denote acquiescence, either with the status quo or with a recent potential departure from the status quo? Does it represent a type of unuttered protest, perhaps meant to signify an objection or a lack of agreement? Might their silence have no legal significance at all? Who makes this determination? And who benefits, and who loses, from a finding that a particular silence does or does not yield legal consequences?[1]
In some contexts, international law assigns specific legal effects to silence or inaction. For example, under the Vienna Convention on the Law of Treaties (VCLT), merely signing certain treaties — without also ratifying them — is not sufficient to make those instruments binding.[2] A separate provision in the VCLT stipulates that a contracting State that fails to explicitly object to a reservation entered by another party within twelve months is considered to have accepted the reservation.[3] Still another provision of the VCLT foresees the adoption of a treaty at an international conference even if one-third of the States are not present or do not vote.[4] As an additional example, an article of the United Nations Convention on the Law of the Sea (UNCLOS) contemplates that certain marine-scientific-research projects may proceed unless the coastal State responds to a notification within four months.[5]
Despite these specific provisions, however, international law does not offer clear general guidance on what could or should be inferred from apparent silence or inaction.
Nevertheless, international actors have long imbued silence with legal significance, at least in some instances.[6] For example, in the jurisprudence of the International Court of Justice (ICJ), acquiescence has led to the enlargement of Norway’s maritime claims vis-à-vis the United Kingdom[7] and a change in the land boundary between Thailand and Cambodia.[8] In the identification of customary international law, which requires evidence of a general practice accepted as law (opinio juris), under certain conditions silence has been treated as both manifestations of such general practice and proof of States’ legal views.[9]
Yet none of these practices has been consistent. Even the ICJ has treated silence differently on different occasions, at times viewing it as legally significant and other times denying it such significance.[10] Moreover, when the International Law Commission (ILC) recently elaborated the preliminary view that under certain circumstances, silence could be regarded as acquiescence in the areas of subsequent treaty practice and identification of customary international law, several States rejected — expressly — part of those proposals as imposing undue burdens and lacking a basis in international law.[11] (Ultimately, the ILC did not budge, though the Commission’s respective commentaries on those matters do consider some of the concerns raised by States.[12])
While it is impossible to construct a general rule on the legal significance of silence in respect of all of the sources of contemporary international law, several scholars have routinely invoked the silence of States and other international actors as proof of support for particular legal views. Not least, this practice has been noticeable, and with apparently increasing frequency, in the jus ad bellum field: the legal regulation of the threat or use of force in international relations.[13] Moreover, where scholars in this field invoke silence as legally significant, those invocations are more often than not submitted in favor of relatively wide claims to use force.[14]
The stakes for invoking silence in this context are immensely high. This is not only because of the obvious importance of the subject matter itself but also because of certain jurisprudential structures of this legal field. Jus ad bellum treaty law is relatively sparse and subject to much debate and contestation. Meanwhile, customary international law on the use of force is often treated, in both theory and practice, as a key means to help resolve legal disputes, fill-in perceived gaps in the law, and further develop doctrine. Yet whether a customary norm has in fact emerged, what its relationship is with the U.N. Charter, and what its precise contours are — all make for their own sets of controversies.
Indeed, recent decades have witnessed voluminous and heated debates over certain key questions regarding the permissible use of force under international law, such as what constitutes an “armed attack”; how to apply jus ad bellum principles of necessity and proportionality; and whether a State may use force preemptively, may engage in “humanitarian intervention,” or may undertake unilateral military action against non-state actors in a foreign territory. An array of States, international organizations, courts, scholars, and non-governmental organizations (NGOs), all relying on the same sources of international law, have often reached remarkably discordant views on these and other pressing jus ad bellum questions.
In many — and perhaps all — of these debates, the purported silence of States and other international actors appears to play a role, whether by inference or by express invocation. Those silences have been deployed, explicitly and implicitly, to ground claims of tacit support for, or opposition to, a particular legal position. At other times, the potential legal significance of silence has been expressly or impliedly disclaimed.
Scholarship provides perhaps the clearest example. For instance, writings on the following military actions (among several others) directly invoke silence as carrying some type of legal significance:[15]
- The military raid in 1976 by Israel in Entebbe, Uganda;
- The military intervention in 1979 by Tanzania in Uganda;
- The airstrikes in 1998 by the United States against al-Qaeda in Afghanistan;
- The military operations in 1999 and 2007–08 by Turkey against the Partiya Karkerên Kurdistanê (PKK) in Iraq;
- The military intervention beginning in 2001 by the United States in Afghanistan;
- The military operations in 2002 and 2007 by Russia against Chechen rebels in Georgia; and
- The military operations beginning in 2014 by an international coalition against the self-described Islamic State of Iraq and Syria (ISIS) in Syria.
As it is impossible at this stage to construct a general doctrinal rule on the significance of silence under international law, these instances of invocation of silence in support of legal arguments may or may not be on a sound juridical footing. And, of course, even if valid as a scholarly effort, academic writings are by no means determinative in discerning what a legal rule is, let alone how it should be interpreted or applied.
Still, legal scholarship often informs debates in all fields of law. And international law is no exception.[16] In fact, the Statute of the ICJ accords the views of prominent international-law writers a particular role in the determination of the rules of law that the Court may rely on in deciding specific disputes.[17] Indeed, one would be hard-pressed to find legal decisions by international courts that do not reference scholarship.[18] Moreover, government lawyers, international organizations, and other actors interested in international law routinely review scholarship to inform their legal analyses. Unsurprisingly, reliance on scholars may increase where the identification, interpretation, or application of the law is subject to greater debate and contestation.
And so, while as a normative matter the silence of States or other international actors may or may not be imbued with legal consequences, as a practical matter it often is — and that is particularly so in the field of jus ad bellum.
With these stakes in mind, in this paper we examine the actual and potential roles of silence as an element of jus ad bellum treaty law and customary international law.[19] By silence, we mean a lack of a publicly discernible response either to conduct reflective of a legal position or to the explicit communication of a legal position.[20] We focus here on the silence of States and the United Nations Security Council as the primary actors who are positioned to shape, interpret, and apply jus ad bellum. We evaluate how silence has been employed by various scholars in making legal arguments in this field, and how silence may have the potential to affect the formation, identification, modification, and termination of various doctrines. To help demonstrate our argument, we zoom in on the contemporary debate surrounding the resort to military action by States against non-state actors in foreign territory without the consent of the territorial government and without authority from the Security Council.[21] While far from new, this debate has gained increased attention and heightened relevance since the advent of the “War on Terror” in late 2001, and again with the targeting of ISIS members in Syria beginning in 2014.[22]
To stress, we take no position here on the substantive merits of the various, and often opposing, legal positions elaborated in contemporary jus ad bellum debates, nor even on whether there is any room for debate in the first place. Instead, we take the existence of these debates as a given and focus on the ways in which writers have invoked — and the ways in which other international actors could use — the silence of others as possible proof of tacit support for, or implied rejection of, particular positions. One of our goals is to help raise awareness of silence as an international-law argumentative technique. Another is to invite a broader engagement with the question of the significance of silence in the identification and development of international law in general and in the law governing the use of force in particular.
We argue that, at least in relation to jus ad bellum, only certain forms of qualified silence — whether of States or of the Security Council — may be capable of contributing to legal effects. We further contend that, due in part to the nature and status of the norms underlying jus ad bellum, those forms of qualified silence ought not to be lightly presumed. Arguably, there is a strong, if rebuttable, presumption that silence alone does not constitute acceptance of a jus ad bellum claim. Be that as it may, in an era seemingly marked by “normative volatility” in this field,[23] States and other international actors should be aware of the possible role that their silence could play in the identification and development of jus ad bellum.
We proceed as follows. In Part II, we outline what we mean by silence in the context of international law. In Part III, we evaluate the actual and potential roles of silence in the jus ad bellum field. And in Part IV, we conclude.
We complement our analysis with an Annex[24] that offers the most comprehensive catalogue to date of communications made by U.N. Member States to the Security Council of measures taken in purported exercise of the right of self-defense under article 51 of the U.N. Charter.[25] The catalogue records more than 400 communications made since the founding of the United Nations in late October 1945 through 2018. These communications reflect the views of the submitting State (or States) on the scope of the right to employ force on the purported basis of self-defense. Notably, U.N. Member States are apparently not made aware of such statements on the use of force as a matter of routine practice.[26] This means that, at least in some instances, States might fail to comment on or otherwise react to other States’ positions on the use of force, not as a deliberate choice but for lack of awareness.
If this is correct, two conclusions follow. The first relates to our suggestion that only qualified silence be accorded potential legal significance: if States are unaware of practices or positions forwarded by other States, it is difficult to see how the silence of those unaware States can carry normative value. The other is that especially in the field of jus ad bellum, the fact that States are not routinely made aware contemporaneously of self-defense communications reported to the Security Council under article 51 is, in our view, a significant concern that ought to be addressed as a matter of priority.
Two methodological caveats should be noted here. First, we catalogue and focus on (apparent)[27] reports of self-defense measures and certain forms of Security Council responses thereto — but without bringing into view the responses of (other) States to those reports. This means that our catalogue gives voice to States that have reported self-defense measures and to the Security Council in response thereto, but not to States that have reacted to such reports. Second, in our review of international-law scholarship, we have covered academic publications in the English and French languages only. Notwithstanding the loss of a broader examination of scholarship in other languages, it is frequently English and French publications that make their way into international judicial decisions and other international legal analyses. It appears that the practice of reliance on silence in the scholarship that we did cover is sufficiently common to suggest that States’ silence in the field of jus ad bellum deserves greater attention than it has been accorded so far.
[2]. See Vienna Convention on the Law of Treaties arts. 11–17, 1155 U.N.T.S. 331 (entry into force Jan. 27, 1980). But see id. at art. 18 (“A State is obliged to refrain from acts which would defeat the object and purpose of a treaty when: (a) it has signed the treaty or has exchanged instruments constituting the treaty subject to ratification, acceptance or approval, until it shall have made its intention clear not to become a party to the treaty; or (b) it has expressed its consent to be bound by the treaty, pending the entry into force of the treaty and provided that such entry into force is not unduly delayed.”) (hereinafter, VCLT). Note that a State that does not contract into a treaty would nevertheless be bound by a rule contained in that treaty at least insofar as that rule is reflective of customary international law.
[3]. See VCLT art. 20(3)(5) (“For the purposes of paragraphs 2 and 4 and unless the treaty otherwise provides, a reservation is considered to have been accepted by a State if it shall have raised no objection to the reservation by the end of a period of twelve months after it was notified of the reservation or by the date on which it expressed its consent to be bound by the treaty, whichever is later.”).
[4]. See VCLT art. 19(2) (“The adoption of the text of a treaty at an international conference takes place by the vote of two thirds of the States present and voting, unless by the same majority they shall decide to apply a different rule.”). [5]. See United Nations Convention on the Law of the Sea art. 252, 1833 U.N.T.S. 3 (entry into force Nov. 16, 1994) (“States or competent international organizations may proceed with a marine scientific research project six months after the date upon which the information required pursuant to article 248 was provided to the coastal State unless within four months of the receipt of the communication containing such information the coastal State has informed the State or organization conducting the research that: (a) it has withheld its consent under the provisions of article 246; or (b) the information given by that State or competent international organization regarding the nature or objectives of the project does not conform to the manifestly evident facts; or (c) it requires supplementary information relevant to conditions and the information provided for under articles 248 and 249; or (d) outstanding obligations exist with respect to a previous marine scientific research project carried out by that State or organization, with regard to conditions established in article 249.”) (hereinafter, UNCLOS) (cited in Sophia Kopela, The Legal Value of Silence as State Conduct in the Jurisprudence of International Tribunals, 29 Austl. Y.B. Int’l L. 87, 90 n.18 (2010)).
[6]. See, among others, Alexis Marie, Le silence de l’Etat comme manifestation de sa volonte (2018); Schweiger, above note 1; Paulina Starski, Silence within the process of normative change and evolution of the prohibition on the use of force: normative volatility and legislative responsibility, 4 J. Use of Force & Int’l L. 14 (2017); Kopela, above note 5; David J. Bederman, Acquiescence, Objection and the Death of Customary International Law, 21 Duke J. Comp. & Int’l L. 31 (2010); Nuno Sérgio Marques Antunes, Acquiescence, in Max Planck Encyclopedia of Public International Law (Rüdiger Wolfrum ed., 2006); Gionato Piero Buzzini, Les Comportements Passifs des Etats et Leur Incidence sur la Réglementation de L’emploi de la Force en Droit International Général, in Customary International Law on the Use of Force: A Methodological Approach 79–117 (Enzo Cannizzaro & Paolo Palchetti eds., 2005); Hans Das, L’estoppel et l’acquiescement: assimilations pragmatiques et divergences conceptuelles, 30 Revue Belge de Droit Int’l 607 (1997); Sir Ian Sinclair, Estoppel and acquiescence, in Fifty Years of the International Court of Justice: Essays in Honour of Sir Robert Jennings 104–20 (Vaughan Lowe & Malgosia Fitzmaurice eds., 1996); Jean Barale, L’acquiescement dans la jurisprudence internationale, 11 Annuaire Français de Droit Int’l Année 389 (1965); I. C. MacGibbon, Customary International Law and Acquiescence, 33 Brit. Y.B. Int’l L. 115 (1957); I. C. MacGibbon, The Scope of Acquiescence in International Law, 31 Brit. Y.B. Int’l L. 143 (1954).
In international scholarly discourse, the legal effects, if any, of silence have often been framed as a contest between the purportedly competing theories of “voluntarism” and “objectivism.” As summarized by Kopela, “voluntarism argues[ that] the legal effects of silence, that is whether silence is legally relevant, depend upon the intention of the silent state. On the contrary, objectivism asserts to base its conclusions not on the intention of this state, but on the impact of silence as a factual situation upon other states.” Kopela, above note 5, at 89 (emphasis added). See also id. at 100 (“Objectivism purports to safeguard the juridical security in international law as expressed in the reliance of states or the international community upon the conduct of a state, whereas voluntarism seeks to preserve the rights and the interests of the silent state, whose will is the legal basis of international law.”). Kopela argues that a “third pillar” ought to be added to “voluntarism” and “objectivism” — namely, that of the “jurisprudential perspective.” Id. at 89.
[7]. See Fisheries (U.K. v. Nor.), Judgment, 1951 I.C.J. Reports, 116, 138–39 (Dec. 18) (hereinafter, Fisheries, Judgment). See further below note 44 and the accompanying text.
[8]. See Temple of Preah Vihear (Camb. v. Thai.), Judgment, 1962 I.C.J. Reports, 6, 23 (June 15) (hereinafter, Temple of Preah Vihear, Judgment). See further below note 41 and the accompanying text.
[9]. See Part II.
[10]. Compare, among others, Asylum (Colom. v. Peru), Judgment, 1950 I.C.J. Reports, 266, 277–78 (Nov. 20) (hereinafter, Asylum, Judgment); Fisheries, Judgment, above note 7, at 139; Rights of Nationals of the United States of America in Morocco (Fr. v. U.S.A.), 1952 I.C.J. Reports, 176, 200–201 (Aug. 27) (hereinafter, Rights of U.S. Nationals); Temple of Preah Vihear, Judgment, above note 8, at 23; Military and Paramilitary Activities in and against Nicaragua (Nicar. v. U.S.A.), Jurisdiction and Admissibility, 1984 I.C.J. Reports, 392, 408–09 (Nov. 26) (hereinafter Military and Paramilitary Activities, Jurisdiction and Admissibility); Sovereignty over Pedra Branca/Pulau Batu Puteh, Middle Rocks and South Ledge (Malay./Sing.), Judgment, 2008 I.C.J. Reports, 12, 50–51 (May 23) (hereinafter, Sovereignty over Pedra Branca/Pulau Batu Puteh, Judgment); with Land and Maritime Boundary between Cameroon and Nigeria (Camer. v. Nig.: Eq. Guin. intervening), Judgment, 2002 I.C.J. Reports, 303, 351, 352–53, 354–55 (Oct. 10) (hereinafter, Land and Maritime Boundary, Judgment); Sovereignty over Pulau Ligitan and Pulau Sipadan (Indo./Malay.), Judgment, 2002 I.C.J. Reports, 625, 650 (Dec. 17) (hereinafter, Sovereignty over Pulau Ligitan, Judgment); Alleged Violations of Sovereign Rights and Maritime Spaces in the Caribbean Sea (Nicar. v. Colom.), Preliminary Objections, 2016 I.C.J. Reports, 3, 25 (Mar. 17) (hereinafter, Caribbean Sea, Preliminary Objections); Question of the Delimitation of the Continental Shelf between Nicaragua and Colombia beyond 200 nautical miles from the Nicaraguan Coast (Nicar. v. Colom.), Preliminary Objections, 2016 I.C.J. Reports, 100, 122 (Mar. 17) (hereinafter, Nicaraguan Coast, Preliminary Objections). For summaries, see below notes 40–43 and the accompanying text.
[11]. See Part II.
[12]. See id.
[13]. With respect to nomenclature regarding this field, there is a tendency, at least in some of the more recent literature on the subject, to replace the generic term jus ad bellum with that of jus contra bellum. See Claus Kreß, The International Court of Justice and the ‘Principle of Non-Use of Force’, in The Oxford Handbook of the Use of Force in International Law 565 n.18 (Marc Weller ed., 2015) (citing to Robert Kolb, Ius contra bellum. Le droit international relatif au maintien de la paix internationale (2d ed., 2009) and Olivier Corten, Le droit contre la guerre (2008)).
[14]. See Part III.D.
[15]. See id.
[16]. See, e.g., William Twining, Ward Farnsworth, Stefan Vogenauer, & Tesón Fernando, The Role of Academics in the Legal System, in The Oxford Handbook of Legal Studies 945 (Mark Tushnet & Peter Cane eds., 2005) (“It cannot be denied, however, that the many thousands of pages published annually in international law journals have an influence on the actual rules enforced and articulated in the legal arena. Again, that influence cannot be easily quantified, yet this much can be said: scholars sometimes help to make the agenda of important international law issues more concrete and well defined. To be sure, that agenda is ultimately the reflection of the various converging interests and conflicts that governments happen to have. Still, there is no doubt that the systematic scholarly presentation of an issue contributes to the discussion of that issue and the sharpening of the respective positions in non-academic settings. Just as governments shift the object of their concern, so do scholars.”).
[17]. Statute of the International Court of Justice art. 38(1)(d), 3 Bevans 1179 (entry into force Oct. 24, 1945) (“The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply: ... subject to the provisions of Article 59, … the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law.”) (hereinafter, ICJ Statute).
[18]. For example, with respect to the field of international criminal law, see Nora Stappert, A New Influence of Legal Scholars? The Use of Academic Writings at International Criminal Courts and Tribunals, 31 Leiden J. Int’l L. 963, 979 (2018) (concluding in part that “[b]oth the quantitative data of citations to academic writings and the qualitative interviews with judges and legal officers indicate that scholarly contributions play a more influential role than its formal categorization as a subsidiary means implies. In international criminal law as a subfield in which international courts and tribunals have played a particularly prominent role in the development of legal rules and principles, this room for judicial creativity also seems to have indirectly opened a door for legal scholars to play a more prominent part in the interpretation, and potentially making, of international law.”) (citations omitted).
[19]. On silence in respect of peacetime cyber operations, see Barrie Sander, The Sound of Silence: International Law and the Governance of Peacetime Cyber Operations, in 11th International Conference on Cyber Conflict: Silent Battle 361–81 (Tomáš Minárik, Siim Alatalu, Stefano Biondi, Massimiliano Signoretti, Ihsan Tolga, & Gábor Visky eds., 2019); on silence in respect of the law of armed conflict, see Sandesh Sivakumaran, Making and Shaping the Law of Armed Conflict, 71 Current Leg. Prob. 119, 152–59 (2018).
[20]. We do not address other concepts pertaining to silence or inaction in international law, for example in relation to a non liquet that could result from the absence of a legal rule altogether or to the duty of a State to refrain from acquiescing in organized activities within its territory directed towards the commission of organizing, instigating, assisting, or participating in acts of civil strife or terrorist acts in another State when those acts involve a threat or use of force. On non liquet, see Daniel Bodansky, Non Liquet, in Max Planck Encyclopedia of Public International Law para. 4 (Rüdiger Wolfrum ed., 2006) (“A non liquet could result either from the absence of a legal rule altogether or from a tribunal’s inability to determine what the legal rule is, that is, it could signify either that the law is silent or obscure. In the first instance, the non liquet would be ontological in nature; in the latter instance, epistemological. If a new situation arose that international law did not address in any way, the result would be an ontological non liquet. In contrast, if a court were to conclude that it could not ascertain the relevant State practice regarding a particular issue, say, the standard of compensation in expropriation cases, the result would be an epistemological non liquet.”) (emphasis added); see also Helen Quane, Silence in International Law, 84 Brit. Y.B. Int’l L. 240 (2014). On the duty to refrain from acquiescing in certain activities involving threat or use of force, see U.N. General Assembly, resolution 2625(XXV) (“Declaration on Principles of International Law concerning Friendly Relations and Co-operation among States in accordance with the Charter of the United Nations”), A/RES/2625(XXV), Oct. 24, 1970 (“Every State has the duty to refrain from organizing, instigating, assisting or participating in acts of civil strife or terrorist acts in another State or acquiescing in organized activities within its territory directed towards the commission of such acts, when the acts referred to in the present paragraph involve a threat or use of force.”).
[21]. See Part III.C.4.
[22]. See Schweiger, above note 1; Starski, above note 6.
[23]. See Starski, above note 6.
[24]. See Annex, HLS PILAC Catalogue of Communications to the Security Council of Measures Taken by United Nations Member States in Purported Exercise of the Right of Self-Defense: October 24, 1945 through December 31, 2018 (Dustin A. Lewis ed., 2019).
[25]. The second sentence of article 51 of the U.N. Charter lays down the following: “Measures taken by Members in the exercise of this right of self-defence shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such action as it deems necessary in order to maintain or restore international peace and security.” Charter of the United Nations art. 51, second sentence, 3 Bevans 1153 (entry into force Oct. 24, 1945) (hereinafter, U.N. Charter).
[26]. See Part III.C.3.
[27]. The reports identified as “article 51 communications” in this paper and in the HLS PILAC catalogue should be considered apparent “article 51 communications” because there has been no authentic and authoritative interpretation under the Charter that each such report does in fact constitute an “article 51 communication.” See Annex. On the concept of “authentic” and “authoritative” interpretation, see below note 188 and the accompanying text. For ease of reading, we do not expressly qualify each identified report as “apparent”; however, that qualification should be considered to implicitly attach to each “article 51 communication” identified in this paper and in the HLS PILAC catalogue.