In a class discussion about this question, there seemed to be one answer that was continually espoused, by many people, and quite vehemently so. Though there were a few variations, the heart of the answer was something along the lines of the following:
To say that S owns x, means that S (or someone on S’s behalf) can defend x (or S’s right to x).
This answer was defended vehemently, even when faced with some of the consequences of this definition of ownership. For instance, this definition seems to preclude a traditional notion of theft (perhaps any notion of theft), as for person R to take x from S (by any means, whether by agreement or force) would simply be R establishing their right to x. In addition to these interesting implications for the traditional notion of theft, there were implications concerning the ability to own persons. By this definition, it would seem that parents own their children, assuming that they defend the children. Note: that parents do [if this is truly the definition of ownership], in fact, own their children, not simply have some duty to protect, or legal/societal right to make decisions on behalf of their children. Furthermore, this ownership would not necessarily dissolve upon the child becoming an adult, unless the parents’ ability to defend the grown child was severed. This same thing, of course, applies to other persons, not simply to the parent/child relationship.
If one then couples this definition of ownership with a mainstream American view of private property, namely that one of the primary duties of government is to protect its’ citizens right to private property (it seems to me that the typical US citizen would assent to this, and quite strongly), it seems to place ownership in the morally permissible category.
There seems to be only three options available to someone concerning this view:
1) Reject this definition of ownership.
2) Accept that it is morally permissible to own another person, and to jettison the traditional notion of theft.
3) Reject that ownership, of any object, is morally permissible, instead moving to the category of morally prohibited.
It seems to me that there are precious few (if any) who would be willing to go the route of (2). (3), while (IMO) more palatable than (2), is something I, at least, would hesitate to do. Thus, the only option that would be left is (1), which as I noted above, seemed to be quite unpopular [even after the implications were discussed]. Also, I am unsure as to what alternative account of ownership to put forth in place of the current.
All of that said, I was curious as to which of the three options others would choose, or if anyone could see a fourth option. (If you think (1) is the way to go, please put forth another definition of ownership.)