Whence the Legitimate Authority of Customary International Law: to Honor State
Consent, or Legitimate Expectations – or Both?
State consent has long been assumed to be the central and even sole source of legal
validity of international law (IL), by the ICJ and International Legal Positivism.
This centrality of state consent, has been challenged for several empirical, conceptual
and normative reasons, especially but not only for customary IL (CIL) This paper explores
such criticisms to reconstruct claims to legitimate authority on behalf of IL in general, and
for ICL in particular: Whence any claims of the sources of IL to offer reasons for judges
for interpretation of IL, and for compliance constituencies to defer to judgments of
international courts, to act any different?
An aim of this paper is to explore whether and how arguments for the centrality of state
consent can provide (partial) support for ICL’s claim to be a legitimate authority, and shed
light on why state consent is neither necessary nor sufficient to give rise to legally binding
obligations – yet why state consent may sometimes be relevant.
Section 1 explores challenges to the current centrality of state consent. States consent
is difficult to discern even for several formal sources (ICJ Statute Art 38) (– not to
mention law making by international organizations – Alvarez 2006 and international
courts, von Bogdandy and Venzke 2011). In particular, ICL, including norms of pacta sunt
servanda and jus cogens, are said to derive and develop from the practice of state. So
treaties may thus bind third parties (Vienna Convention Art 38, Pellet 2000, 37-38;
Meron). The criteria of state practice and opinio juris are not only unsatisfactory ‘nonmoralized social facts’ as evidence of state consent, but their vagueness leave judges
striking discretion – and are conceptually contested to boot.
Section 2 therefore identifies reasons to value state consent even when, and especially
when, “consent is falling out of favour” (Collins 2018). Reasons with varying scope of
application and weight include compliance, specification, reduction of domination and enhanced fairness. Such arguments help assess both the value of state consent and
proposed improvements. One aim is to identify the conditions, limitations – and
incompleteness of state consent as necessary or sufficient conditions for some of the
states’ legal obligations. These help identify any justification of such circumscribed state
consent for the legitimate authority of IL and ICL. Proposed reconstructions and
improvements presumably retain some functions for state consent, specified in light of
Section 3 starts to situate state consent in alternative broader normative accounts of
promise-keeping. In particular, the paper explores the normative premise of “what we
owe to other people when we have led them to form expectations about our future
conduct. “ (Scanlon 1990, 199-201, 208; MacCormick 1972) . This is certainly only one
normative requirement on behavior, and the social practice of promises including treaties
is only one of several means to create such expectations. Other behaviour, as part of
practices or not, can also create such expectations. Other overriding duties may hold
independent of any social practice.
Section 4 brings this account to bear on the roles and current conditions and scope of
state consent in creating valid obligations under IL, and on the claims of ICL in particular
– including its defining characteristics. Topics may include the norm that new jus cogens
norms retroactively void treaties (Vienna Convention art 64); a more plausible
reconstruction of ‘tacit consent’, why coerced peace treaties may still be legally binding,