Ownership is the kind of authority that involves a real power to order things to certain ends. It is clear that humans can do this with respect to inanimate objects. We take advantage of a things nature teleology or directedness, but order it extrinsically to achieve some end of our own. One of my favorite examples of this is electricity. We take advantage of an electron’s nature tendency to move toward lower potentials in an electric field and we can use this toward our own ends.
We do this similarly with animate beings as well. We trim and form plants to a particular shape to climb a ladder, for example. We might give grain to an ox or horse and train them over time to react to certain stimuli in particular ways. As with the electron, there are ways of imposing upon the thing in certain ways that will direct their natural tendencies to the ends we desire.
This is a real power that we have over non-rational beings. Rational being are a different story. By their very nature possessed of free will, a rational animal has the capacity to direct itself to certain ends. Whereas inanimate being have a natural tendency with a sort of physical necessity and animate being have a sort of passive or receptive natural tendency based on sensitive stimuli, humans are active in ways that brutes are not.
The freedom of the free will is in that the deliberation over goods is interior. The sort of sensitive “judgement” that an animal makes when it flees a predator or pursues a prey has a particular natural tendency which rational judgement does not. The rational animal is capable of taking in the perceptions and judge them in themselves rather than being moved by them.
Whereas man can direct an inanimate natural tendency or an animate sensitive tendency to his own ends, principally because they physically or biologically necessary, man cannot direct the rational tendency, that is will, of other men. Ownership of other men is not simply immoral, but impossible. A man cannot actually have that sort of power over other men.
Now, men may crush as much as possible another man’s will and subject him to tortures such that his sensitive appetites or tendencies overwhelm his will, but he can never truly have ownership of another man’s will.