Three versions of the principle of proportionality exist in international law, with different constitutional functions. The horizontal version 1 applies, inter alia, in the field of countermeasures. The principle here refers to the relation between action (breach of international law) of the state and the admissible reaction of another state. The diagonal version 2 concerns the relation between and national public interest and particular interests, of individuals (for example, in international humanitarian law), or of investors. The vertical version 3 refers to the relation between a global public interest, for example, in free trade, and particular interests of states.
This chapter shows that the constitutionalization of and within international law is a fragmented process which, moreover, engages domestic constitutional law. It is not bringing about a ‘superconstitution’ over and above domestic law and all international subfields. After clarifying the key terms, notably constitutionalization, constitutionalism, and constitutional law, it explains the sectoral constitutionalization of various international organizations and the constitutionalization of the private (economic) realm. It concludes that we find (only) constitutional fragments.
Anne Peters, Heike Krieger and Leonhard Kreuzer
As a standard bridging law and other spheres of normativity, due diligence is pervasive across numerous areas of international law. This paper defines the features and functions of due diligence, illustrating how the concept's development reflects structural changes in the international legal order. Concerning their content, due diligence obligations can be separated into two overlapping types: procedural obligations and obligations relating to States' institutional capacity. Thus, due diligence serves to manage risks, compensate for States' freedoms being circumscribed through legalisation, expand State accountability and possibly stabilise the international order through ‘proceduralisation’. However, it is argued that due diligence cannot be characterised as a general principle of international law due to its diverse content in different fields of international law and its dependence on accompanying primary rules. Finally, it is contended that due diligence introduces certain risks, particularly by diluting States' substantive obligations and contributing to the rise of ‘informal’ international law.