Of Spiders and Bees 185manner of a geometric demonstration. Wolff also maintained, though
somewhat vaguely, that the rules of natural law, when applied to the special-
ist fi eld of interstate relations, underwent a modifi cation and took on “a
certain new form.”
Th e part of law that arose from human free will comprised two of Wolff ’s
categories of law: stipulative and customary. Th is was the law made from
below, by the free consent of the states themselves, for their own perceived
benefi t. Th is consent took either of two forms: express consent in the case of
the stipulative law (i.e., treaty law) and tacit consent in the case of the cus-
tomary law. Treaty law and customary law were therefore seen by Wolff as
being, so to speak, two sides of the same man- made coin. Both were con-
tractual in character, meaning that they are binding only on parties to the
arrangement in question. Consequently, they do not qualify as universal in-
ternational law, as the necessary law of nations does. Wolff had little regard
for these two types of law. Like Pufendorf, he held them to be, strictly speak-
ing, not part of the general law of nations at all, any more than private con-
tracts are part of the civil law of states. Th eir study therefore belongs to “the
history of this or that nation” rather than to the general “science of the law
of nations.” Moreover, if a treaty or customary arrangement were found to
be contrary to natural law, then it would thereby cease to be legally binding,
even on the parties to it.
Th e fourth and fi nal type of law identifi ed by Wolff — to which he gave the
woefully unfortunate label of “voluntary” law— was a sort of hybrid between
natural law and positive (or man- made) law. Strictly speaking, it was man-
made. But it was not a product of the free will of humans, as treaty law and
customary law were. Instead, it arose from what Wolff called the “presumed”
consent of nations. Th is “presumed” consent, however, must be under-
stood to be the conclusively presumed consent of all nations, without excep-
tion. In other words, states had no choice but to accept and observe this
“voluntary” law.
Th e Wolffi an voluntary law was a sort of manservant to natural law. It
amounted, in eff ect, to a resuscitation of the medieval substitution theory of
the ius gentium— a key indicator of Wolff ’s scholastic temperament. Natu-
ral law was stated to be “a fi xed and immovable foundation” of the voluntary
law. Th e task of the voluntary law was to implement or apply natural law to
the practical circumstances of everyday international relations. Th e only