226 A Positive Century (1815–1914)what the law actually is. Questions of what the law should be were for moral
phi los o phers and other such dreamers. Th is point has commonly been put
in terms of the distinction between “is” and “ought”— a dichotomy famously
insisted on by the Scottish phi los o pher David Hume in the eigh teenth cen-
tury. Th e scientifi c lawyer deals with the is. Metaphysicians, moralists, and
other such speculators traffi c in the ought.
With these general points in mind, it is now possible to explore nineteenth-
century positivism in somewhat more detail— and in doing so, to take care-
ful note of the three distinct versions in which it came.
Th e Th ree Variants of Positivism
Nineteenth- century positivism came in, broadly speaking, three variant
forms. A lack of attention on historians’ part has left them without accepted
labels, but descriptive titles can be readily proferred. Th e fi rst may be termed
the “empirical” variant. It could as easily be called the “inductive” approach
(and sometimes has been). It stressed the making of international law by
the collective action of the states themselves, primarily in the form of cus-
tomary law. Th e second version will be termed the “common- will” approach.
It focused on international law as arising out of explicit agreements between
states, chiefl y in the form of written treaties. Th e third variant is the “volun-
tarist” approach, which stressed international legal obligations as arising
out of the voluntary ac cep tance of rules by each state individually, on its
own. In the briefest possible summation, it may be said that the empirical
approach was based on state practice, the common-will version on agree-
ment, and the voluntarist variant on individual state will. Th e empirical
perspective was an organic outgrowth of the pragmatic wing of the Grotian
tradition of the seventeenth and eigh teenth centuries. Th e other two were
innovations of the nineteenth century.
Th e Empirical Variant
Th e core belief of the empirical (or inductive) variant of positivism was the
thesis that the content of international law is (or at least should be) dis-
cerned on an empirical and observational basis, by a close study of actual