A theory of Justice: Revised Edition

particular orders designed to advance the interests of a dictator or the
ideal of a benevolent despot. Often there is no clear answer to this ques-
tion. The point of thinking of a legal order as a system of public rules is
that it enables us to derive the precepts associated with the principle of
legality. Moreover, we can say that, other things equal, one legal order is
more justly administered than another if it more perfectly fulfills the
precepts of the rule of law. It will provide a more secure basis for liberty
and a more effective means for organizing cooperative schemes. Yet be-
cause these precepts guarantee only the impartial and regular administra-
tion of rules, whatever these are, they are compatible with injustice. They
impose rather weak constraints on the basic structure, but ones that are
not by any means negligible.
Let us begin with the precept that ought implies can. This precept
identifies several obvious features of legal systems. First of all, the ac-
tions which the rules of law require and forbid should be of a kind which
men can reasonably be expected to do and to avoid. A system of rules
addressed to rational persons to organize their conduct concerns itself
with what they can and cannot do. It must not impose a duty to do what
cannot be done. Secondly, the notion that ought implies can conveys the
idea that those who enact laws and give orders do so in good faith.
Legislators and judges, and other officials of the system, must believe that
the laws can be obeyed; and they are to assume that any orders given can
be carried out. Moreover, not only must the authorities act in good faith,
but their good faith must be recognized by those subject to their enact-
ments. Laws and commands are accepted as laws and commands only if
it is generally believed that they can be obeyed and executed. If this is in
question, the actions of authorities presumably have some other purpose
than to organize conduct. Finally, this precept expresses the requirement
that a legal system should recognize impossibility of performance as a
defense, or at least as a mitigating circumstance. In enforcing rules a legal
system cannot regard the inability to perform as irrelevant. It would be an
intolerable burden on liberty if the liability to penalties was not normally
limited to actions within our power to do or not to do.
The rule of law also implies the precept that similar cases be treated
similarly. Men could not regulate their actions by means of rules if this
precept were not followed. To be sure, this notion does not take us very
far. For we must suppose that the criteria of similarity are given by the
legal rules themselves and the principles used to interpret them. Never-
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Equal Liberty

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theless, the precept that like decisions be given in like cases significantly
limits the discretion of judges and others in authority. The precept forces
them to justify the distinctions that they make between persons by refer-
ence to the relevant legal rules and principles. In any particular case, if the
rules are at all complicated and call for interpretation, it may be easy to
justify an arbitrary decision. But as the number of cases increases, plausi-
ble justifications for biased judgments become more difficult to construct.
The requirement of consistency holds of course for the interpretation of
all rules and for justifications at all levels. Eventually reasoned arguments
for discriminatory judgments become harder to formulate and the attempt
to do so less persuasive. This precept holds also in cases of equity, that is,
when an exception is to be made when the established rule works an
unexpected hardship. But with this proviso: since there is no clear line
separating these exceptional cases, there comes a point, as in matters of
interpretation, at which nearly any difference will make a difference. In
these instances, the principle of authoritative decision applies, and the
weight of precedent or of the announced verdict suffices.
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The precept that there is no offense without a law