The most intuitive conception of law regards it as derivative from or subordinate
to ideal morality. This conception characterizes natural law and many positivistic
approaches. It holds that if law is morally justified, then its justification necessarily
derives from the fact that it reflects or mirrors ideal morality. I distinguish
between practical idealness and epistemic idealness. Whereas practical idealness focuses
on publicity and perfect compliance, epistemic idealness refers to (possible)
perfect knowledge of information that is necessary to follow and apply rules.
Now, law is capable of reflecting or mirroring ideal moral principles only if it
can meet the epistemic demands of ideal moral theory. In fact, compliance with
ideal moral principles presupposes factual knowledge that often is not easily available.
In order to perform this epistemic function, law must include the functioning
of reliable truth-searching institutions. In most legal systems, courts are both
truth-searching and conflict-settling institutions. Michel Foucault and Robert
Nozick have stressed that a central feature of modern national law is that it establishes
justice enforcement bodies that are also designed to provide public knowledge
that is indispensable for applying elaborate rules and principles. Carlos Alchourron
and Eugenio Bulygin say that “gaps of knowledge” (i.e., the absence of
reliable information about the features of an individual case) can hinder adjudication
in a way that is similar to “normative gaps”. Potential epistemic completeness
is then a condition of possibility of many ideal moral and legal principles.
Traditional areas of international law lack an institutional system endowed
with fact-finding and truth-ascertaining powers. Therefore, international legal
rules must refer to incontestable conditions of application because such rules
must be self-applied by states without the possible epistemic arbitration of a
neutral party. Consider jus in bello, that is, the system of legal rules that regulate
permissible behavior in war. Jeff McMahan has argued that the theory of just war
should differentiate between just and unjust combatants in terms of their fulfillment
of jus ad bellum requirements, equating just combatants with civilians. But
he also observes that this ideal moral view cannot be translated into jus in bello in the present circumstances because there are no judicial bodies that can assess
and establish the jus ad bellum status of belligerent parties. This means that, in
the absence of truth-ascertaining institutions, ideal moral principles are irrelevant
for international law whenever they contemplate contestable conditions
of application.