Defining Soft Law in International Law
Despite its common usage, the notion of soft law continues to cause confusion and contestation among international lawyers. Some scholars resist the term, arguing that it has come to signify a too wide and disparate set of phenomena, making any single definition or taxonomy impossible.  Others argue that the conjunction of the two words ‘soft’ and ‘law’ inevitably invites attempts to ascribe legality to political documents, threatening to undermine the status of positive international law proper and blur the boundary between law and politics.2 Both the definition and standing of soft law have, thus, been the subject of substantial doctrinal debate.
The term itself would seem to indicate a residual category—not quite positive international law, but somehow aspiring thereto or at least thought to influence legal interpretation. A common approach is thus to define soft law in the negative, as lacking one or several properties normally ascribed to international law; for example precise normative content, enforceability, and formal legal status. 
While such a multi-dimensional model can be useful in terms of more clearly distinguishing between different types of soft law for purposes of legal interpretation, it also significantly expands the ambit of what may be characterized as soft law. It may, for instance, imply the elevation of rules and instruments traditionally considered outside the boundary of international law,5 notably texts authored by and/ or addressed to non-state actors, such as the Montreux Document on military and security companies, or the Maastricht Principles on extraterritorial obligations of states. This is an issue of particular importance in the field of human rights, where NGOs and scholars have a strong presence and long history in terms of advancing human rights issues.
Such a definition may secondly imply a downgrading of formally hard law commitments lacking a sufficient degree of normative precision or enforceability so as to be de facto non-binding. Despite important institutional developments in international human rights law in terms of review, petition, and adjudication, effective enforcement is still lacking in many areas. Similarly, important parts of international human rights law—notably in the area of economic, cultural, and social rights—have always built on aspirational commitments and principles of collective responsibility that, despite on-going developments, are not easily implemented or adjudicated.
The issue of definition thus also raises obvious political questions: do we risk overreaching and thus conflating law and politics in a way that fundamentally undermines the privileged position of human rights law as a subset of positive international law? Or, vice versa, are we selling short those parts of international human rights law that do not resemble traditional treaty language?
From a more conceptual perspective, any attempt to define soft law simply as ‘not-hard law’ could be argued to run all the same risks of other negative definitions in international law.10 The criteria applied vary considerably among scholars,11 and the definitional problem is thus pushed back into a larger discussion of the concept of international law, its functions and its transformation/2
The contributions to this volume show that the roles of soft law often challenge the boundaries of international human rights law, both in term of its nature and its fields of application. While some lawyers have greeted these developments and corresponding ‘new sources of international law’ with optimism/3 others see the fragmentation of international law as a ‘legal jungle’ of incoherent interpretation that may end up creating obligations ex nihilo, and consequently advocate in favour of legal non-proliferation/4
The doctrinal debate over the increased use of soft law seems to reflect a more fundamental rift between those keen to uphold international law as a system that produces foreseeable and determinable outcomes, based on a limited yet objectively identifiable and binding set of international obligations,^ and those who accept that the expansion of international norms, with varying normative density, implies a more subjective and dynamic interpretation/6
- 10 See e.g.: P. Alston, ‘The “Not-a-Cat” Syndrome: Can the International Human Rights Regime Accommodate Non-state Actors?’, in Non-state Actors and Human Rights, ed. P. Alston (Oxford: Oxford University Press, 2005): 3—6; P. Alston, ‘The “Not-a-Cat” Syndrome: Re-thinking Human Rights Law to Meet the Needs of the Twenty-first Century’, in Progressive Governance for theXXI Century (Florence: European University Institute and New York University School of Law, 2000) (proceedings of the conference involving Presidents Clinton and Cardozo, Prime Ministers Blair, D’Alema, and Jospin, and Chancellor Schroeder): 128^4.
- 11 Scholars vary considerably in terms of the criteria to be applied however. Chinkin proposes
- (1) legal form, (2) precision, (3) authorship, (4) addressees, (5) theory of responsibility, and (6) enforcement. See: Chinkin in Shelton (2000); Wellens and Borchardt, and later, Aldestam apply four criteria: (1) binding requirement of certain conduct or omission formulated by subjects with authority and following pre-established procedures; (2) knowledge, ability, and will of the addressees to comply; (3) precision of the norm; and (4) means to enforce the norm. See: Karel C. Wellens, and G. M. Borchardt, ‘Soft Law in European Community Law’, European Law Review vol. 14 (1989): 267—321 at 285; Adelstam (2004): 11—36 at 17. More recently, Ellis talks about: (1) Normativity and Justiciability,
- (2) Enforceability, (3) Precision, and (4) Formal legal status. See: Ellis (2012): 313—34.
- 12 Ellis (2012); Nasser (2008): 12.
- 13 E. Riedel, ‘Standards and Sources: Farewell to the Exclusivity of the Sources Triad in International Law’, European Journal of International Law vol. 2 (1991): 58—84 at 62; G. Von Glahn, Law among Nations: An Introduction to Public International Law (New York: Macmillan, 1981).
- 14 A number of scholars have written on and enumerated different viewpoints in this ongoing debate. See in particular: K. Nicolaidis and J. L. Tong, ‘Diversity or Cacophony? The Continuing Debate of New Sources of International Law’, Michigan Journal of International Law vol. 25 (2004): 1349—75 at 1361; J. H. H. Weiler and Andreas L. Paulus, ‘The Structure of Change in International Law or is There a Hierarchy of Norms in International Law?’, European Journal of International Law vol. 8 (1997): 545—65; C. Leben, ‘Symposium: The Changing Structure of International Law Revisited: By Way of Introduction’, European Journal of International Law vol. 8 (1997): 399^08; and J. A. C. Salcedo, ‘Reflections on the Existence of a Hierarchy of Norms in International Law’, European Journal of International Law vol. 8 (1997): 583—95.
- 15 Weil (1983): 77; J. Klabbers, ‘The Redundancy of Soft Law’, Nordic Journal of International Law vol. 65 (1996): 167-82; Klabbers (1998).
- 16 U. Fastenrath, ‘Relative Normativity in International Law’, EJIL vol. 4 (1993): 305^0, at 324.
-  See John Cerones chapter in this volume for more information. See also: J. Ellis, ‘Shades ofGrey: Soft Law and the Validity of Public International Law’, Leiden Journal of International Law vol.25 (2012): 313—34; Salem H. Nasser, Sources and Norms of International Law (Berlin: Galda and WilchVerlag, 2008).
-  P. Weil, ‘Towards Relative Normativity in International Law?’, American Journal of InternationalLaw vol. 77 (1983): 413^2; J. Klabbers, ‘The Undesirability of Soft Law’, Nordic Journal ofInternational Law vol. 67 (1998): 381—91.
-  Andrew T. Guzman and Timothy L. Meyer, ‘International Soft Law’, Journal of Legal Analysis vol.171 (2010): 171-225, at 172.
-  C. Chinkin, ‘Normative Development in the International Legal System’, in Commitmentand Compliance: The Role of Non-binding Norms in the International Legal System, ed. D. Shelton(Oxford: Oxford University Press, 2000); K. C. Wellens and G. M. Borchardt, ‘Soft Law in EuropeanCommunity Law’, European Law Review vol. 14 (1989): 267-321, at 285; M. Adelstam, ‘Soft Law inthe State Aid Policy Area’, in Soft Law in Governance and Regulation, ed. U. Morth (Cheltenham: ElgarPublishing, 2004): 11-36 at 17; Ellis (2012).
-  Nasser (2008) and Ellis (2012).
-  The Montreux Document on Pertinent International Legal Obligations and Good Practices for StatesRelated to Operations of Private Military and Security Companies duringArmed Conflict (17 Sept. 2008).
-  Maastricht Principles on Extraterritorial Obligations of States in the area of Economic, Social andCultural Rights (28 Sept. 2011).
-  Klabbers (1998); G. Noll, Negotiating Asylum: The EU Acquis, Extraterritorial Protection and theCommon Market of Deflection (The Hague: Martinus Nijhoff, 2000).
-  As pointed out by Weil: ‘A rule of treaty or customary law may be vague, “soft”; but ... it does notthereby cease to be a legal norm.’ Weil (1983): 414.