c and very
close to Plato in time, is taken up with this distinction and gives
us a clue to the juristic problems of the time.

Another example may be seen in Aristotle's well-known discussion in
the Nicomachean Ethics. It is significant that Greek thinkers always
couple custom and enactment; things which today we contrast. These
were the formal bases of legal authority. So Aristotle considers, not
natural _law_ and positive _law_, but what is just in itself--just by
nature or just in its idea--and what derives its sole title to be just
from convention or enactment. The latter, he says, can be just only
with respect to those things which by nature are indifferent. Thus
when a newly reconstituted city took a living Spartan general for its
eponymus, no one was bound by nature to sacrifice to Brasidas as to an
ancestor, but he was bound by enactment and after all the matter was
one of convention, which, in a society framed on the model of an
organized kindred, required that the citizens have a common heroic
ancestor, and was morally indifferent. The distinction was handed
down to modern legal science by Thomas Aquinas, was embodied in
Anglo-American legal thought by Blackstone, and has become staple.
But it is quite out of its setting as a doctrine of _mala prohibita_
and _mala in se_. An example of the distinction between law and
rules of law has become the basis of an arbitrary line between the
traditionally anti-social, penalized by the common law, and recently
penalized infringements of newly or partially recognized social
interests. Although the discrimination between what is just and right
by nature and what is just because of custom or enactment has had a
long and fruitful history in philosophical jurisprudence and is still
a force in the administration of justice, I suspect that the permanent
contribution of Greek philosophy of law is to be found rather in the
distinction between law and rules of law, which lies behind it and has
significance for all stages of legal development.

Roman lawyers came in contact with philosophy in the transition from
the strict law to the stage of equity and natural law, and the contact
had much to do with enabling them to make the transition. From a
purely legal standpoint Greek law was in the stage of primitive law.
Law and morals were still largely undifferentiated. Hence Greek
philosophical thinking of a stage of undifferentiated law and morals
lent itself to the identification