152 Reason and Its Rivals (ca. 1550– 1815)interpersonal relations rather than about interstate relations. Nowhere is
this more evident than in discussions of the law of self- defense, which fo-
cused principally on the rights of individuals to use force when assailed by a
wrongdoer. Indeed, just- war doctrine in general had arisen out of debates
over whether individual Christians should refuse to perform military
ser vice.
For a long time, this individualistic character of natural law did not pose
a great diffi culty. Th e reason was that, in the Middle Ages, it was universally
accepted that rulers were subject to the basic laws of human conduct just as
ordinary persons were. Th e setting in which those rules applied was, of course,
very diff erent, depending on whether the actor was a monarch or a peasant.
But the rules themselves were conceded to be the same. Th is “demo cratic”
state of aff airs became ever less tenable, however, as nation- states came
increasingly to be seen as impersonal corporate bodies, with interests dis-
tinct from those of their citizens and subjects— distinct even from those of
the rulers regarded in their individual capacities.
Th ere came, therefore, to be grounds for thinking that the rules govern-
ing the conduct of states were— at least to some extent— diff erent from those
governing the relations of individuals. And it was this idea that became the
core of later international law. Th e question then immediately presented it-
self: where were the rules governing the relations of states to come from, if
not from natural law? Fortunately, an answer was at hand— or at least the
raw material for an answer. Th e necessary rules for interstate conduct could
come from the ius gentium.
In order for this to be feasible, though, it was going to be necessary to
think about the ius gentium in rat her diff erent terms than before. Th is would
not prove to be an easy task. It will be recalled that, during the Middle Ages,
the tendency had been to associate the two bodies of law closely, by way of
either the substitution or the emanationist theory. Th e emanationist the-
ory, which posited the closest bond between the two, continued to exert a
hold. Soto, for example, endorsed it in his contention that the ius gentium
included “everything that men have drawn as conclusions from natural
principles.”
Second thoughts, however, were growing on this subject. Nowhere is this
more evident than in the somewhat confused opinion(s) of Vitoria. As a
staunch Th omist, he naturally had an inclination toward the emanationist