Much of what might be called the “classical” theory of the just war was formulated
prior to the advent of modern states and the emergence of doctrines of state sovereignty.
The classical writers understood the morality of war to be only one dimension of a
unified body of natural law that governs individual human action in much the way that
the laws of nature govern the nonhuman world, except that the human subjects of natural
law were thought to enjoy free will, which enabled them, unlike natural objects, to violate
at least some of the laws to which they were subject.
Natural law was thought to be
addressed primarily to the conscience of the individual person and was only derivatively
The doctrines of the classical just war theorists were therefore largely
individualist in character – that is, they were focused on whether or when it was
permissible for individuals to go to war and what it was permissible or impermissible for
them to do in war.
Working within the natural law tradition, the classical just war theorists understood
themselves to be discovering and articulating objective moral truths.
In contrast to later
theorists in the just war tradition, they did not, at least for the most part, formulate moral
principles by reference to what they believed the likely consequences would be if people
were to accept and attempt to follow them.
Nor did they try to determine what principles
potential adversaries might realistically be able to agree to accept, or could rationally
accept, for governing their relations with one another.
These ways of reasoning about the
selection of principles for the governance of war had to await the development of
institutional means of regulating relations among actual and potential adversaries.
principles of classical just war theory therefore made few concessions to purely
Just war theory has traditionally been divided into two sets of principles, those
governing the resort to war (
jus ad bellum
) and those governing the conduct of war (
The classical theorists tended to regard
jus in bello
as dependent on
jus ad bellum
in the sense that what it is permissible for an individual to do in war depends on whether
his war is just, and in particular on whether it is being fought for a “just cause” – that is,
an aim that is sufficient to justify the resort to war.
Writing in the first half of the
sixteenth century, Francisco de Vitoria argued that soldiers “
must not go to war
“the war seems patently unjust,” even when they are ordered to do so by a legitimate
authority, for “one may not lawfully kill an innocent man on any authority, and in the
case we are speaking of [when soldiers are confident that their war is unjust] the enemy
must be innocent.”
By “innocent” Vitoria meant “having done no wrong.”
Suárez, writing roughly half a century later, reaffirmed Vitoria’s view: “No one may be