A legal system is a coercively enforced system of public rules addressed to rational persons and aimed at regulating their conduct for the sake of their common good and so providing a framework for their social cooperation (TJ 207). At a minimum, the rule of law requires the regular and impartial administration of these rules. For example, like cases must be treated alike. This much is required by the very idea of a legal system as a system of public rules. When the “rules” are administered – interpreted and/or applied – in a manner stained by bribery, threats, prejudice, bias, and the like, those subject to them are regulated by something other than public rules.

In a sufficiently complex and long-enduring legal system, this minimum requirement of the rule of law, which Rawls dubs “justice as regularity,” will constrain the discretion of legal officials in so-called “hard cases” for which there exists no applicable rule antecedently established either by legislation or by past judicial decisions. The reason for this is that, if it is to be decided in a regular and impartial fashion and so as a matter of law, the hard case must be decided in a manner sensitive to, at least consistent with, the framework, the distinctions, reasons, and so on, established by the existing rules. In a sufficiently complex and long-enduring legal system, then, the discretion of legal officials is almost always constrained in this way. This minimal rule of law requirement – no more than the regular and impartial administration of the rules – works to constrain at least a certain kind of injustice, namely that of coercing persons to comply with arbitrary commands rather than public rules (TJ 209).