Customary International Law Requiring States to Grant Nationality
juris when the norm would be logical or sensible to ensure international
coexistence and cooperation.
The Court presumes the existence of rules of customary international law when
it can logically deduce those norms from other rules or principles of international
law.22 First, the Court can deduce the existence and content of customary
international law from treaties.23 In the advisory opinion of Legal Consequences
for States of the Continued Presence of South Africa in Namibia (South West
Africa) notwithstanding Security Council Resolution 276, the Court used the
Charter of the United Nations to interpret the application of the rules of selfdetermination.24 Also, in the Territorial and Maritime Dispute (Nicaragua v
Colombia), the Court held that a rule expressed in the United Nations Convention
on the Law of the Sea applied to the situation, despite Colombia not being a party
to that treaty.25 As such, the existence of a treaty governing the situation can be
good evidence that customary international law also governs. 26 This is certainly
the case when the treaty is intended to codify customary international law, rather
than resolve a ‘lack of consensus and of clear, agreed rules’.27 Thus, the states
must have either ‘unilaterally assumed’ or ‘accepted’ the obligations ‘by conduct,
by public statements and proclamations, and in other ways’28 or adopted a ‘very
definite, very consistent course of conduct’29 where the practice is in alignment
with the treaty.30 But the Court has even applied treaty provisions by analogy to
cases clearly not covered by the treaty, such as in the Corfu Channel case, where
the Court applied the obligation to notify ships of minefields during times of war
in the 1907 Hague Convention (VIII) relative to the Laying of Automatic
Submarine Contact Mines to peacetime situations.31 In this manner, actual state
practice is not necessarily required if the norm can be presumed and is not
rebutted.32
Second, the Court can deduce a presumption in favour of customary
international law from other norms of customary international law. This approach
can take the form of identifying the full scope of existing rules, such as when, in
22
23
24
25
26
27
28
29
30
31
32
See Jurisdictional Immunities Case (n 10) 126–32 [67]–[72]; Fisheries Jurisdiction Case
(n 11) 175.
See, eg, Armed Activities on the Territory of the Congo (Democratic Republic of the Congo v
Uganda) (Judgment) [2005] ICJ Rep 168, 62 [161]–[162], 242 [214], 251 [244] (‘Armed
Activities on the Territory of the Congo’); Jurisdictional Immunities Case (n 10) [72].
Legal Consequences for States of the Continued Presence of South Africa in Namibia (South
West Africa) notwithstanding Security Council Resolution 276 (1970) (Advisory Opinion)
[1971] ICJ Rep 16, 31 [52] (‘Legal Consequences’).
Territorial and Maritime Dispute (Nicaragua v Colombia) (Judgment) [2012] ICJ Rep 624,
666 [114] (‘Nicaragua v Colombia Territorial and Maritime Dispute’); Delimitation of the
Continental Shelf Between Nicaragua and Colombia Beyond 200 Nautical Miles from the
Nicaraguan Coast (Nicaragua v Colombia) (Judgment) [2016] ICJ Rep 208, 213 [16]
(Robinson J) (‘Nicaragua v Colombia Continental Shelf Case’).
See, eg, North Sea Continental Shelf Cases (n 3) 25; Furundžjia Trial Judgment (n 10) 53 [138].
Medvedyev v France (European Court of Human Rights, Grand Chamber, Application No
3394/03, 29 March 2010) 30 [92].
See North Sea Continental Shelf Cases (n 3) 25 [27].
See ibid 25 [28].
See Furundžjia Trial Judgment (n 10) 53 [138].
See Corfu Channel Case (n 20) 22; ‘Memorial Submitted by the Government of the United
Kingdom of Great Britain and Northern Ireland’, Corfu Channel (United Kingdom v Albania)
[1947] ICJ Pleadings 19, 37–38 [63]–[65].
See, eg, Legal Consequences of the Separation of the Chagos Archipelago from Mauritius
in 1965 (Advisory Opinion) [2019] ICJ Rep 95, 132 [151]–[152] (‘Chagos Archipelago
Advisory Opinion’).
117