The Lotus Principle and Customary International Law

Article By: Sanskruti Yagnik, SVKM’s Pravin Gandhi College of Law

This blog is an extension of an article on the Lotus Principle in the ICJ Jurisprudence. In this piece I shall explain the evolution of Customary International Law with the Lotus Case.

Since the establishment of International Law there have been two main sources of law – treaties between the states and customs. Most recently, after the World War II, the accepted definition of custom can be found in the Statute of the International Court of Justice (ICJ), in its Article 38(1)(b). The Court in its jurisprudence basically settled two necessary components of the constitution of custom; the state practice and the opinio juris.

The jurisprudence of the Permanent Court of International Justice (PCIJ) and also its successor, has helped to clarify many issues concerning the formation of Customary International Law, in cases such as the Lotus Case (1927),the Asylum Case (1950), the North Sea Continental Shelf (1969), and the Nicaragua Case (1986). In this blog piece I will specifically be focusing on the Lotus Case and its jurisprudence establishing the foundation for Customary International  Law.

The Lotus case gave an important dictum on creating customary international law. France had alleged that jurisdictional questions on collision cases are rarely heard in criminal cases, because States tend to prosecute only before the flag State. France argued that this absence of prosecutions points to a positive rule in customary law on collisions. The Court disagreed and held that, this:

would merely show that States had often, in practice, abstained from instituting criminal proceedings, and not that they recognized themselves as being obliged to do so; for only if such abstention were based on their being conscious of having a duty to abstain would it be possible to speak of an international custom. The alleged fact does not allow one to infer that States have been conscious of having such a duty; on the other hand, as will presently be seen, there are other circumstances calculated to show that the contrary is true”.

Two element approach

Under the “two element approach”, a rule of customary international law may be said to exist where there is ‘a general practice’ that is ‘accepted as law’. These two requirements, “the criteria which [the International Court of Justice] has repeatedly laid down for identifying a rule of customary international law”[1], must both be identified in any given case to support a finding that a relevant rule of customary international has emerged.

As one author has explained, “Without practice (consuetudo), customary international law would obviously be a misnomer, since practice constitutes precisely the main differentia specifica of that kind of international law. On the other hand, without the subjective element of acceptance of the practice as law the difference between international custom and simple regularity of conduct (usus) or other non-legal rules of conduct would disappear”.

Oppenheim states that “the terms of Article 38(1)(b) … make it clear that there are two essential elements of custom, namely practice and opinio juris” And the recent edition of Brierly states that “[c]ustom in its legal sense means something more than mere habit or usage; it is a usage felt by those who follow it as obligatory … in the words of Article 38(1)(b) of the Statute, we must examine whether the alleged custom shows a ‘general practice accepted as law’”

Customary international law is not a matter of “individual subscription”. Sometimes it is also underlined that what matters is consent of a group of States, not necessarily the whole international community. But even if it is possible to specify a set of States whose acceptance is significant, how do we know that these States have expressed their acceptance? This is a purely epistemological matter which, however, seems to be the utmost. The thing is that, in the case of international law, clear and explicit expression of will by States occurs quite rarely. Of course, explicitly and clearly, States express their will to be bound by treaties or unilateral acts (assuming that the unilateral act will not be understood as the omission). But even in case of treaty-like bargain, verbosity is not obvious.

To say that customary law consists of only an objective element means that whatever States do is legal, so there is no real distinction between what ought to be and what is. In this perspective, therefore, opinio juris as differentia specifica is somehow analogical to basic norm applied by H. Kelsen. It is mostly elusive and vague but it is the key premise of law. While in the case of treaties, consent is expressed in a direct way, in the case of customary law, it is expressed in a “non-written form”. Moreover, the only constitutive element of customary law is opinio iuris. This concept was described by the ICJ this way:

“Although the passage of only a short period of time is not necessarily, or of itself, a bar to the formation of a new rule of customary international law on the basis of what was originally a purely conventional rule, an indispensable requirement would be that within the period in question, short though it might be, State practice, including that of States whose interests are specially affected, should have been both extensive and virtually uniform in the sense of the provision invoked; – and should moreover have occurred in such a way as to show a general recognition that a rule of law or legal obligation is involved.”


The World Court has yet to commit itself on the key question of the nature of customary law. And it has been delphic on the more specific question of opinio juris. In the Lotus Case, it spoke in psychological terms, holding that states must be “conscious of having a duty” in order for a rule of customary law to be present. Similarly, in the North Sea Continental Shelf Cases, the Court referred to opinio juris as “a subjective element” in the composition of customary law. More specifically, it is described as “a belief,” which appears to have a psychological flavour. Further in this apparently psychological vein, the Court held that states “must . . . feel that they are conforming to what amounts to a legal obligation.” (para. 77) The Court does not explicitly say, however, whether this subjective element or belief refers to the positions of each state individually, on its own, or to the subjective stance of the community as a whole. In later cases, the Court has held back from this overtly psychological phraseology.

[1] Jurisdictional Immunities of the State (Germany v. Italy: Greece intervening), Judgment, I.C.J. Reports 2012, p. 99, at p. 122, para. 55

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