A theory of Justice: Revised Edition

(Nullum
crimen sine
lege),
and the requirements it implies, also follow from the idea of a legal
system. This precept demands that laws be known and expressly promul-
gated, that their meaning be clearly defined, that statutes be general both
in statement and intent and not be used as a way of harming particular
individuals who may be expressly named (bills of attainder), that at least
the more severe offenses be strictly construed, and that penal laws should
not be retroactive to the disadvantage of those to whom they apply. These
requirements are implicit in the notion of regulating behavior by public
rules. For if, say, statutes are not clear in what they enjoin and forbid, the
citizen does not know how he is to behave. Moreover, while there may be
occasional bills of attainder and retroactive enactments, these cannot be
pervasive or characteristic features of the system, else it must have an-
other purpose. A tyrant might change laws without notice, and punish (if
that is the right word) his subjects accordingly, because he takes pleasure
in seeing how long it takes them to figure out what the new rules are from
observing the penalties he inflicts. But these rules would not be a legal
system, since they would not serve to organize social behavior by provid-
ing a basis for legitimate expectations.
Finally, there are those precepts defining the notion of natural justice.
These are guidelines intended to preserve the integrity of the judicial
21. See Lon Fuller, 
Anatomy of the Law
(New York, The New American Library, 1969), p. 182.
209
38. The Rule of Law

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process.
22
If laws are directives addressed to rational persons for their
guidance, courts must be concerned to apply and to enforce these rules in
an appropriate way. A conscientious effort must be made to determine
whether an infraction has taken place and to impose the correct penalty.
Thus a legal system must make provisions for conducting orderly trials
and hearings; it must contain rules of evidence that guarantee rational
procedures of inquiry. While there are variations in these procedures, the
rule of law requires some form of due process: that is, a process reason-
ably designed to ascertain the truth, in ways consistent with the other
ends of the legal system, as to whether a violation has taken place and
under what circumstances. For example, judges must be independent and
impartial, and no man may judge his own case. Trials must be fair and
open, but not prejudiced by public clamor. The precepts of natural justice
are to insure that the legal order will be impartially and regularly main-
tained.
Now the connection of the rule of law with liberty is clear enough.
Liberty, as I have said, is a complex of rights and duties defined by insti-
tutions. The various liberties specify things that we may choose to do, if
we wish, and in regard to which, when the nature of the liberty makes it
appropriate, others have a duty not to interfere.
23
But if the precept of no
crime without a law is violated, say by statutes, being vague and impre-
cise, what we are at liberty to do is likewise vague and imprecise. The
boundaries of our liberty are uncertain. And to the extent that this is so,
liberty is restricted by a reasonable fear of its exercise. The same sort of
consequences follow if similar cases are not treated similarly, if the judi-
cial process lacks its essential integrity, if the law does not recognize
impossibility of performance as a defense, and so on. The principle of
legality has a firm foundation, then, in the agreement of rational persons
22. This sense of natural justice is traditional. See H. L. A. Hart,