it is to a better which may be in its turn transcended, not to a single immutable best.
Aristotle found in the society of his time men who were not capable of political reflection, and who, as he thought, did their best work under superintendence. He therefore called them natural slaves.
For, according to Aristotle, that is a man's natural condition in which he does his best work. But Aristotle also thinks of nature as something fixed and immutable; and therefore sanctions the institution of slavery, which assumes that what men are that they will always be, and sets up an artificial barrier to their ever becoming anything else.
We see in Aristotle's defence of slavery how the conception of nature as the ideal can have a debasing influence upon views of practical politics.
His high ideal of citizenship offers to those who can satisfy its claims the prospect of a fair life; those who fall short are deemed to be different in nature and shut out entirely from approach to the ideal.