I'm busy working on a paper. I'm trying to make sense of what Kant and Locke said in the context of self-ownership. But it isn't just of historical interest, I'm pretty sure that what I have to say about Kant and Locke can easily be transferred to what current self-ownership theorists have to say.
Kant says something like: "We are masters over ourselves, but we are not owners of ourselves." He then offers what might be seen as two arguments against self-ownership: The first is the problem of self-reflexivity (how can the proprietor and property be the same thing?), while the second is the problem of viewing persons as things (we can own things, but persons are not things). In addition, Kant tells us that we are to act in a way that is consistent with the humanity-in-ourselves, and he thinks this means a prohibition on suicide, masturbation, and a bunch of other things.
Meanwhile, Locke insists that we own ourselves, that God also owns us, and that we have legitimate authority over our children to tell them what to do, and so on. Locke insists that there are restrictions on what we can do with ourselves, something that we are told we own. We can't committ suicide, or harm ourselves, and this is explained, at least in part, by appeal to the fact that God ultimately owns us, and that he commands us to preserve ourselves and others.
There are ways to work with the concept of ownership and these views. There are ways to reconcile everything that Locke says, and everything that Kant says. But all of the ways are clunky, and require adjustments to the concept of ownership. I think I have a better idea. I think we have access to concepts that make making sense of Locke, Kant, and the special case of children easier. Those concepts are guardianship and stewardship. I think Kant's view is best expressed as a self-stewardship view, while Locke's view is best viewed as a self-guardianship view. Children, meanwhile, don't count as things to be owned, but as wards to be guarded.
To be an owner over something, call it x, is to have most of the sticks in the bundle of rights that make up the concept property. This is A.M. Honore's view. There are 12 "sticks" ("incidents" more formally) in the bundle: I have a right to use, transfer, derive income, and so on, things that I own.
For Honore, there are no "essential" rights in order to be able to say that we "own" something. Others disagree. These people say that alienability (right to sell or transfer), and disposability (right to destroy) are fundamental features of ownership. They say that we are not really owners of x unless we can sell x or smash/destroy x. I have similar linguistic intuitions with these other theorists. I really think that it makes no sense to talk of "owning" something unless I can really sell it or destroy it.
If these others and I are right, then not being permitted to sell ourselves into slavery, or not being permitted to harm ourselves or commit suicide, are inconsistent with the principle of self-ownership, strictly understood. At least some self-ownership theorists agree, and bite a big bullet. They say we can sell ourselves into slavery (no one really thinks permitting suicide or harm to ourselves is a devastating objection to self-ownership anymore).
Turning to the distinction I want to introduce: We can distinguish ownership, stewardship, and guardianship in the following way.
To be an owner is to have legitimate authority over what is to be done with something that we own. To be an owner is to choose the sake that will be targeted when it comes to things we own. For example, we can smash our telephone, or use it to make a phone call, or do whatever we like with it, even on a whim. There is no special moral obligation that we have to heed with respect to what we own (we only have to heed general moral obligations that are moot about specific things--like, we can't hurt others, even when what we use to hurt others is something we own).
To be a guardian over something is to have legitimate authority over the thing guarded on the condition that we be guided by the sake of our ward. We are under a moral obligation to always regard what is best for our ward when we deal with our ward. For example, we are morally required to do what is best for our children.
Meanwhile, to be a steward is to have legitimate authority over a thing on the condition that we heed the sakes of third parties when we are making decisions with respect to the thing we are a steward over. We are under a moral obligation to heed those sakes. For example, we can be a steward over a forest for the sake of future generations, and we are under a moral obligation to preserve the forest for the sake of those future generations. Or, we might be a trustee (I think this is just a special case of stewardship) over a trust fund for someone's children. And so on.
If we have to heed the sake of the humanity-in-us, as Kant says, when we do things with ourselves, then it might be better to view ourselves as self-guardians (or self-stewards, I'm not clear). It is not difficult to see how someone can be a master over x, while not an owner, when we think of what we mean by the concept of guardianship. A guardian is a master, but his or her having this legitimate authority is conditioned by a moral obligation to heed the sake of the ward (in this case, the humanity-in-us). We do not own ourselves, strictly speaking.
For Locke, we have been given legitimate authority over ourselves by God, but only on the condition that we act in accordance with what God wants for his property, us. We are self-stewards. Both masters over ourselves, and under a moral obligation to heed God's sake when we do things with what we are stewards over, ourselves. We do not own ourselves, strictly speaking.
The same might be said of children (and the elderly suffering from neuro-degenerative diseases). We are not owners of our children, but guardians over them. We are required to heed their sake when we have dealings with them.
I think this makes better sense of Kant and Locke than other attempts. I think guardianship and stewardship are good concepts to use in some cases in place of ownership. We can now begin to wonder about when it is fitting to view ourselves as stewards or guardians, rather than owners, when it comes to some special categories of things. Like our pets, our children, and certain cultural artefacts (like Rembrandt paintings and so on).