In this chapter I will connect the previous discussion of procedural rights with the debates about the rule of law. In Book V of the Nicomachean Ethics, Aristotle gives one of the first accounts of the rule of law when he says: “we allow only reason, not a human being, to be ruler.” Aristotle then divides political justice into two parts. “One part of the politically just is natural, and the other part legal. The natural has the same validity everywhere alike, independent of its seeming so or not.” This characterization of the natural part of justice is sometimes associated with the so-called natural duties of justice, specifically with the substantive duties to promote just institutions. But, it seems that Aristotle, at least at that point in his Ethics, is referring to something procedural, what might be called “natural fairness.”

I am interested in seeing what the normative jurisprudential support is for a minimalist version of habeas corpus in international law. In my view, the writings of H. L. A. Hart and Lon L. Fuller about the internal aspect of rules or the inner morality of law concern an issue that is similar to what Aristotle meant by the natural part of justice, namely that part of natural fairness that stays the same from society to society, and perhaps even outside of particular societies – for instance, in the international arena. Indeed, Hart spoke of “natural procedural justice” and Fuller spoke of a “procedural version of natural law.” In this respect one could ask whether there is something like a natural duty to support procedures, such as habeas corpus, that provide minimal fairness for those who have been incarcerated or detained. And if there is such a duty, is it part of the inner morality of law? In his eighth desiderata of the rule of law, Fuller mentions such things as habeas corpus as an aspect of procedural due process, but he does little more than mention it; Hart does not mention it at all. But in my view both legal theorists focus as much on procedural as substantive justice.