Indeed so deeply embedded in modern man is the principle
that prima facie human beings are entitled to be treated alike
that almost universally where the laws do discriminate by
reference to such matters as colour and race, lip-service at
least is still widely paid to this principle. If such discriminations
are attacked they are often defended by the assertion
that the class discriminated against lack, or have not yet developed,
certain essential human attributes; or it may be said
that, regrettable though it is, the demands of justice requiring
their equal treatment must be overridden in order to preserve
something held to be of greater value, which would be jeopardized
if such discriminations were not made. Yet though
lip-service is now general, it is certainly possible to conceive
of a morality which did not resort to these often disingenuous
devices to justify discrimination and inequalities, but openly
rejected the principle that prima facie human beings were to
be treated alike. Instead, human beings might be thought of
as falling naturally and unalterably into certain classes, so
that some were naturally fitted to be free and others to be
their slaves or, as Aristotle expressed it, the living instruments
of others. Here the sense of prima-facie equality among men
would be absent. Something of this view is to be found in
Aristotle and Plato, though even there, there is more than a
hint that any full defence of slavery would involve showing
that those enslaved lacked the capacity for independent existence
or differed from the free in their capacity to realize some
ideal of the good life.