The Complete Aristotle (eng.)

nature. The law of which I speak is a sort of
convention—the law by which whatever is taken in war is supposed to
belong to the victors. But this right many jurists impeach, as they
would an orator who brought forward an unconstitutional measure:
they detest the notion that, because one man has the power of doing
violence and is superior in brute strength, another shall be his
slave and subject. Even among philosophers there is a difference of
opinion. The origin of the dispute, and what makes the views invade
each other’s territory, is as follows: in some sense virtue, when
furnished with means, has actually the greatest power of exercising
force; and as superior power is only found where there is superior
excellence of some kind, power seems to imply virtue, and the
dispute to be simply one about justice (for it is due to one party
identifying justice with goodwill while the other identifies it
with the mere rule of the stronger). If these views are thus set
out separately, the other views have no force or plausibility
against the view that the superior in virtue ought to rule, or be
master. Others, clinging, as they think, simply to a principle of
justice (for law and custom are a sort of justice), assume that
slavery in accordance with the custom of war is justified by law,
but at the same moment they deny this. For what if the cause of the
war be unjust? And again, no one would ever say he is a slave who
is unworthy to be a slave. Were this the case, men of the highest
rank would be slaves and the children of slaves if they or their
parents chance to have been taken captive and sold. Wherefore
Hellenes do not like to call Hellenes slaves, but confine the term
to barbarians. Yet, in using this language, they really mean the
natural slave of whom we spoke at first; for it must be admitted
that some are slaves everywhere, others nowhere. The same principle
applies to nobility. Hellenes regard themselves as noble
everywhere, and not only in their own country, but they deem the
barbarians noble only when at home, thereby implying that there are
two sorts of nobility and freedom, the one absolute, the other
relative. The Helen of Theodectes says:
Who would presume to call me servant who am on both sides
sprung from the stem of the Gods?
    What does this mean but that they distinguish freedom and
slavery, noble and humble birth, by the two principles of good and
evil? They think that as men and animals beget men and animals, so
from good men a good man springs. But this is what nature, though
she may intend it, cannot always accomplish.
    We see then that there is some foundation for this difference of
opinion, and that all are not either slaves by nature or freemen by
nature, and also that there is in some cases a marked distinction
between the two classes, rendering it expedient and right for the
one to be slaves and the others to be masters: the one practicing
obedience, the others exercising the authority and lordship which
nature intended them to have. The abuse of this authority is
injurious to both; for the interests of part and whole, of body and
soul, are the same, and the slave is a part of the master, a living
but separated part of his bodily frame. Hence, where the relation
of master and slave between them is natural they are friends and
have a common interest, but where it rests merely on law and force
the reverse is true.
VII
    The previous remarks are quite enough to show that the rule of a
master is not a constitutional rule, and that all the different
kinds of rule are not, as some affirm, the same with each other.
For there is one rule exercised over subjects who are by nature
free, another over subjects who are by nature slaves. The rule of a
household is a monarchy, for every house is under one head: whereas
constitutional rule is a government of freemen and equals. The
master is not called a master because he has science, but because
he is of a certain character, and the same remark applies to the
slave and the freeman. Still there may be a science for the master
and science for the slave. The science of the slave would be such
as the man of Syracuse taught, who made money by instructing slaves
in their ordinary duties. And such a knowledge may be carried
further, so as to include cookery and similar menial arts. For some
duties are of the more necessary, others of the more honorable
sort; as the proverb says, ‘slave before slave, master before
master.’ But all such branches of knowledge are