This is a repair of Locke's argument. I was amused when I learned this; I didn't set out to repair his argument and indeed I did not explicitly read any Locke until I heard I was following him. This doesn't surprise me, this is what influence means; to change the thoughts of large numbers of people. They don't have to know you're doing it and indeed it seems obvious that once you have large influence, many people are going to learn your ideas through osmosis.
I'm writing this basically because I find I don't want to link to the old version, for various reasons.
Two notes. Epistemologically speaking, a full definition is a proof, because a full definition must explicitly show each condition under which it does not obtain. Otherwise, the definition invites invalid use. A full proof achieves this by being explicit about assumptions. Second, each premise of this definition-proof can be proven by showing that the opposite proposition is self-contradictory.
Here we go.
You control your body. Actually that's the definition; whatever controls your body is you.
(This is because, using a different definition, I would not be able to interact with 'you' but instead would interact instead with whatever controls your body. I would expand the definition if bodies ever became alienable property. The first step would be to reverse the definition; whatever it is that you directly control is your body; this is to deal with brain-scanning revealing sub-consciousnesses that do not have access to gross motor control, but only a neuronal subset.)
To continue controlling your body, you need to remain alive. Let me define life.
Life: every living thing can be assigned goals. If it ever becomes unable to strive for any goals, it stops being alive.
This definition makes the statement above tautological; to control your body is to make it serve your goals. To continue serving your goals you need to be able to strive for goals. (This also means the definition covers aliens.)
A specific goal all life has is to harvest and control energy. If not, thermodynamics #2 would steal all their available energy and they would perish. If life is defined without this property of goals, it would not be self-sustaining and thus we would not have anything observable to define; it would all have starved to death long ago.
(Test the goals by attempting to interrupt them. The living thing should divert energy to maintain the goal. Note that if you attempt to assign a goal to a nonliving thing, it will be contradicted when they do not divert energy to maintain that goal. Even if you define a threat to them, they will never react to that threat. As always, this is an attempt to codify an intuitive definition; it cannot be proven, only tested against the pre-existing intuition on the subject.)
So, all living things must control their environment to remain alive.
Now, if I have the right to interrupt your control, for consistency you must have the right to interrupt my control. We are, at the level necessary for this proof, identical beings, and therefore cannot have divergent rights. But, by this, I can interrupt your control of my control, and thus retain my control; a contradiction. It is hypocritical to interfere with someone else's body. Therefore, the only valid right is to respect each other's self control.
This is essentially an example of Basic Ethics (1.1), and is the basis of self-ownership.
Self-ownership: the controller of a particular living body is that body's owner. It is wrong to attempt to contravene this ownership. (I leave defining 'direct control' up to practical considerations, as this does not seem to be a common point of contention.)
So, you have ownership of your body in an attempt to control your surroundings, with some expectation of success. Consider the reverse; if you had no expectation of control, you would not attempt the action. Assume for some reason you want to pick up a rock, and so you do. If you had known in advance that you would be prevented from controlling that rock for your 'some reason,' you would not have picked it up. Whenever I see a lifeform attempt to control their surroundings, I can assume they expected some level of success.
Therefore, since I want you to not interfere with my manipulations of the environment, and you're almost identical to me, it cannot be right for me to interfere with your manipulations of the environment. Thus, we expect to own our environment, as an extension of our self-ownership.
There are some exceptions. Insane people's expectations cannot be matched with outcomes, and indeed this forms a decent definition of insanity. Also, people can be mistaken, expecting something that they have no good reason to expect. Both these cases create a contradiction in the logic at the very base; they cannot properly be assigned goals, because they cannot or will not properly defend those goals. As an example, someone may expect to control the quantum state of the atoms of my body, but of course they have no good reason, and indeed as my atoms evolve they will be unable to deflect them toward any goal they might be assigned. If that were the only goal they could be assigned, they would immediately 'die,' according to the definition.* Thus, for this goal, they cannot be considered alive, and thus cannot have self-ownership, and thus their expectation of control cannot be supported as ownership.
*(This makes me realize that goals that can't fail, such as expecting my atoms to evolve randomly, fail as goals because they define control as choosing the absence of control.)
I include this restriction by saying the expectation of control must be reasonable. They must have the faculties of reason, and the faculties must accord with their expectation. (Plants, therefore, cannot own anything, even though they are alive.)
I conclude that ownership is defined as reasonable expectation of control.
In human society, the reasonable expectation of control is achieved through security. Now why is this?
There have always been, and every reason to believe there always will be, people who wish to contravene ownership, either by guile or force. Thieves and robbers, essentialy, and the latter when state-scaled are called warmongers. Because of this, to reasonably expect to retain your property requires you to secure it against these threats, just as to retain control of your body requires you harvest energy, and defend it both from decay and from the attacks of other organisms.
I own my wallet. I can reasonably expect to control it, because I am part of a society that prevents theft first by moral condemnation and second by the police. Similarly, my society itself is protected by the army. (While I'm Canadian, it seems America has been, for some time, playing global police by disincentivizing non-Israeli territory-conquering wars.)
My expectation of control of my wallet is empirically reasonable as well; it has never been stolen. So if it is stolen, does that mean I was wrong that I could reasonably expect to control it, and thus the theft is a non-theft?
The answer to that is no, and I've done that on purpose by using the word 'expect.' Obviously, an omniscience would clearly know that my wallet was going to be stolen, but the reasons available to me at the time clearly lead me to expect it won't be stolen. No matter how much you spend on security, there will always be some way to circumvent it. And indeed, if there were not, there would be no point in defining theft, because it would be impossible.
I would also like to be pedantic about the moral position of the thief; if they had no reasonable expectation of controlling the wallet after it was taken from my pocket, they would not have tried to take it. And thus they, knowing I had reason to expect to retain my wallet* they knowingly violated that reasonably expectation, and supplanted their own. As logical objects, we are not different enough to possibly justify such an asymmetry, and thus all thefts are wrong, even according the thief; theft is hypocritical.
*(Indeed, if I had no such expectation, why would I have taken it with me outside? Would I have ever bothered to acquire one at all?)
This strongly suggests a method for changing an object from unowned to owned; secure it against threats to your control. Right now, the moon is unowned, as nobody can expect to affect events on its surface. Once a transportation corridor is established, someone will own the parts of the moon they can prevent from being conquered by third parties. (Within reason.) Kindly note that this doesn't necessarily require an army; a simple contract may suffice (plus some anti-vandalism patrols.) Similarly, deep-sea habitats generally don't need to fight off pirates, although when deep-sea travel becomes cheap, it will become necessary to stop delinquents from damaging the property, and may become necessary to stop some state-level threats as well.
Nevertheless, as long as reasonable steps are taken, it is wrong to attempt to take or destroy someone else's expectation of control.
Having defined this, there is but a short hop to universal ethics. Short version; humans want to be good. If everyone knew it was wrong to violate reasonable expectation of control, very simple, cheap, and peaceful methods of security may suffice for nearly all property.
While this definition applies to sentient aliens, I don't know how, if at all, it applies to the less conscious life forms of Earth. I am a carnivore, so I suspect it does not. My first instinct is to say that nonhuman life forms cannot create security structures, and this immediately makes me think that even if they did, it isn't obvious that my argument that (since I have values, I have to respect yours) applies across significantly different species, because the way they have values is going to turn out to be qualitatively different.
You can check this idea by referencing children, who have the kind of cognitive differences we might see in aliens. The rules for ownership are not entirely symmetrical in this case.
An interesting objection I have seen is; 'What about part ownership, such as shares?' What we've said here is that ownership of a single object can be divided into parts, of which the ownership is absolute.
Example; you and your sibling each own half of a restaurant, and have hired a manager to run it. Naively, it appears the manager is controlling the restaurant. However, what happens if you and your sibling both decide to fire the manager, or otherwise override their decisions? Similarly, if you and your sibling have a disagreement on whether to fire the manager, you cannot both achieve your goal, so whose goal can we reasonably expect will be achieved? That person is the real owner. If the restaurant is controlled by anyone else, it is because of delegation of control.
Given a whole apple, multiple people cannot all eat the whole thing, though multiple people can eat a part of it. Similarly, given one car, it can only go in one direction. The passengers may agree on the direction, but only one person controls the direction. This is true of all objects; there can be only one owner, because there can be only one controller, and thus only one person who can reasonably expect to control it. (Though of course there are often, even frequently, violations of ownership in the real world that are not criminal per se. As an Anarcho-formalist, I think we'd all be happier if we actually respected the formal truth of these situations.)
You can test the ownership of any real-world object by asking various people to try to control it. It is unambiguous if only one person's goals are realized. If there are multiple people, you can fall back upon the reasonableness test, though at least the control test will narrow the candidates.
So yeah, I have found again that Communism can't work. Someone has to control the stuff, which is exactly what Russia discovered in the Soviet system.
Of course, that word 'reasonable' isn't entirely clear. People lie. You can always make the argument that you expected to control an object, you just can't always reasonably, truthfully do so. In addition, people are wrong. They did expect to control it, but not for any good reason and thus it wasn't reasonable, but of course they don't realize that, and they may convince other people to not realize it either.
It's a judgement call. That is why the head of a court is called a judge.* Nevertheless, it is in principle possible to determine who had good reason to expect control, and who did not. It just isn't feasible, which reflects back and means precision in defining ownership is overkill anyway; you can't unambiguously determine ownership in contentious real-world situations regardless.
*The Five Factor personality test gave me this idea. Folk philosophy tends to settle close to the actual truth. And in fact, common law can be almost entirely derived from the principle of reasonable expectation of control, including the fact that the reason part requires a judgement call and thus a judge.
I believe that's everything. Let me know if I've forgotten something, again; as usual one of my primary motivations for writing this is to help ensure it's correct.