Sophists had shaken the foundations of all traditional institutions, and their thesis that slavery is contrary to nature had become through the Cynics a prominent social theory.635 The thought on the subject had crystallized into two leading doctrines—one including benevolence in justice, and hence denying the right of slavery; and the other identifying justice with the rule of the stronger, and hence upholding slavery as based on mere force.636
The practical Aristotle, an upholder of slavery, not from tradition, but through conscious belief in its economic necessity, thus takes his stand midway between the two opposing theories. He champions the old view of natural slavery, but rejects the basis of mere force for that of morality and benevolence.637
His thesis is that slavery is a natural and necessary relation in human society, not accidental or conventional. The slave, being property, which is a multitude of instruments (ὀργάνων πλῆθος), is an animate instrument (ὄργανον ἔμψυχον) conducive to life (πρὸς ζωήν).638
He is just as necessary to the best life of the citizen as are inanimate instruments, and will be, until all tools work automatically, like the mythical figures of Daedalus or the tripods of Hephaestus.639
The slave is a servant in the realm of action (πρᾶξις), not of production (ποίησις). He is not a producer of commodities (ποιητικός), but of services (πρακτικός),640 and just as property is merely a part or member (μόριον) belonging wholly to something else, so the slave, as property, belongs entirely to his master, and has no true existence apart from him.641
From these facts, the whole nature and power of the slave are evident. One who, though a human being, is merely property is a natural slave, since he is naturally not his own master, but belongs to another, in whom he finds his true being.642