Building Anew 419subject to the very important proviso that any state that actually voices an
objection to a customary rule as it is forming is thereby exempted from ap-
plication of the law. Th is opportunity to opt out of rules of customary law
came to be labeled, reasonably enough, as the “persistent- objector” principle
(although perhaps “express- objector” principle would be a better term).
Th e status of this persistent- objector principle remains unclear. Some law-
yers have maintained, very matter- of- factly, that it is part of international
law. Brownlie speculated that the principle would become increasingly im-
portant in the future, as a counterweight against an increasing “majoritarian
tendency” in international law. Firm judicial evidence in its favor is, how-
ever, sparse and ambiguous at best. Some support for it was evident in two
World Court judgments in the early 1950s. But a clear judicial endorsement
of the persistent- objector theory remains elusive. For present purposes, it is
only necessary to note its practical eff ect: that it goes far toward bridging the
gap between those who support majority rule in the making of customary law
and those (i.e., the voluntarists) who oppose it.
Th e broad contours of the postwar positivist debate over customary law
within the positivist camp may be summed up rapidly. Th ere were three
groups. One of them, including writers like Kelsen and Virally, held to a
pure legislative view of customary law, without allowance for a persistent-
objector caveat. A second group, including Brownlie, accepted majority rule
in customary law in principle, but only subject to allowing opting out by
per sis tent objectors. Th e third group— now usually known as “voluntarists”—
comprising writers such as Arangio- Ruiz and Weil, held to the contractual
theory, asserting that even customary rules are binding on states only with
their actual consent, and hence that customary law is, at root, merely tacit
treaty making. In practice, the great majority of positivist lawyers were in
the second or third of these groups.
Th e Socialists
It was only aft er 1945, when the Soviet Union emerged as an active partici-
pant in global politics and lawmaking, that socialist perspectives on the
subject came to the attention of a wider audience. Th e seminal event was the
election of Krylov to the World Court. He was a professor fi rst at the Univer-
sity of Leningrad and later headed the Department of International Law at