One of the things that one deals with in positive
law is the question of whether or not it's
a force for good or a force for evil.
When the positive law is engaged in setting
out formalities to allow voluntary transactions
to take place, it works for the good.
Uh, but the old maxim which says that, “Whatever
is pleasing unto the prince has the force
of law” carries with it the real danger
that tyrannical rulers will essentially announce
that natural law principles need not be followed,
and that the state can impose upon individuals
whatever rules that it wants.
So, to take the most ancient example slavery
is always inconsistent with natural law because
it doesn't respect the autonomy and equal
autonomy of all individuals.
Nonetheless, slavery was countenanced by positive
law, so that what you do is you see many legal
systems based upon natural law, systematically
flouting it on this one vital issue.
And, in the end, the importance of natural
law here is it gives you a powerful way in
which you can criticize the way in which the
particular system operates, and to point out
the dangers of positivism if what positive
means that the sovereign has an untrammeled
will, and can do whatever he or she wants to his
subjects.
