154 Reason and Its Rivals (ca. 1550– 1815)law in 1601– 3. Th ese were published in 1612 as A Treatise on Laws and God
the Lawgiver. Th is opus contained his exposition on the topic at hand.
Regarding natural law itself, Suárez off ered nothing dramatically new. He
wrote in the rationalistic tradition of Aquinas, holding natural law to con-
sist of “self- ev ident principles of conduct,” toget her w it h “t hose points which
follow necessarily and by a pro cess of obvious inference from the said prin-
ciples.” Natural law, in other words, concerns rules that are “inherent in
nature.” Where Suárez made an important break with the past was in his
treatment of the ius gentium. In par tic u lar, he made two important innova-
tions that would chart the future of international law. First, he explicitly re-
jected both the emanationist and the substitution theories. Second, he as-
serted that the ius gentium, when properly understood, must be regarded as
a law between states as such. In both of these respects, Suárez’s exposition
resuscitated ideas fi rst broached (if only in barest outline) nearly a thousand
years earlier, by Isidore of Seville. Suárez’s discussion, however, was con-
siderably more detailed and systematic than Isidore’s bare outline had been.
Suárez’s affi nity with Isidore’s ideas about natural law and the ius gentium
was made clear, for a start, in a negative way— in his explicit rejection of
both the substitution and the emanationist theories of the Middle Ages, con-
cerning the relation of the ius gentium to natural law. Th e substitution the-
ory, it will be recalled, held the ius gentium to be, eff ectively, a secondary (and
second- rate) form of natural law, that is, a modifi ed version of natural law
suitable for a fallen humanity expelled from the Garden of Eden. Th e true
position, Suárez maintained, is that there is only one body of natural law and
that it is suffi ciently fl exible to govern humanity in both its prelapsarian and
postlapsarian conditions. He also expressly rejected the emanationist the-
ory, insisting instead that anything which is logically deducible from the
basic, self- evident principles of natural law must actually be natural law in
its own right. Th is is because natural law is, by defi nition, a comprehensive
logical system comprising basic principles (or axioms) plus the propositions
deducible from them.
Th e ius gentium, in Suárez’s opinion, falls into the category of “positive
law,” employing a term that had been devised in the Middle Ages. Positive
law, he explained, is human law, “devised and established proximately by
men.” Precisely because positive law is a fruit of human initiative and free
will, it is not derivable from natural law by the force of logical necessity. It