Libertarianism cannot be uniquely defined by referring to initiation as a standard to distinguish between aggressive and defensive coercive acts, because the concept of initiation relies on a more fundamental idea about who ought to own which objects in the first place.
Indeed.
The foundation of libertarianism is the homesteading principle.
The reason the government’s claim to an entire (previously empty) continent is not legitimate (according to the libertarian) is that the government did not homestead the land (or acquire it through a voluntary exchange)
The homesteading principle is not sufficient, as you yourself imply in the bolded passage above.
What is needed is a principle or principles governing how property is acquired in general. Homesteading is just one of several ways in which property can be acquired. It seems to me that there are three distinct ways: homesteading, voluntary exchange, reciprocation. When I say “distinct” I mean that these principles do not all derive from some other more fundamental principle. These have to be taken as axioms. But they also presuppose a concept of property. So we need a definition of property as well, which is another axiom. Given these four axioms (what property is, and the three distinct ways in which it can be acquired) there is no possibility for self-defense. So we actually need a fifth axiom providing for self-defense.
I’ve been working on reducing the entire libertarian ethics to a set of as few principles as possible. Here’s an unpolished draft of what I have so far, and I’d be appreciative of any comments or criticisms.
I. Principle of Property
Classes of Ownership:
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Unconditional and Unlimited Ownership: the owner has the right to use the thing in any way he pleases, and to forcibly exclude others from the use of that thing in any way
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Unconditional and Limited Ownership: the owner has the right to use the thing in a particular way, and to forcibly exclude others from the use of that thing in any way which would cause him to be unable to use the thing in the way that he has a right to use it
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Conditional and Unlimited Ownership: the owner has the right, if certain conditions are satisfied, to use the thing in any way he pleases, and to forcibly exclude others from the use of that thing in any way
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Conditional and Limited Ownership: the owner has the right, if certain conditions are satisfied, to use the thing in a particular way, and to forcibly exclude others from the use of that thing in any way which would cause him to be unable to use the thing in the way that he has a right to use it
II. Principle of Reciprocity
Property Violation: a property violation is the use in any way of an owned thing without the consent of the owner of that thing; or the use of an owned thing in any way which prevents the use of that thing in a particular way by the person who has the right to use that thing in that particular way, and without his consent; the violator of property is the tortfeasor, the person whose property was violated is the victim
Retribution:
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Destruction or Damage: if a person commits a property violation against another person, and thereby causes damage or destruction to the thing concerned, then the victim becomes the owner of some thing of the tortfeasor which is equivalent to that which the tortfeasor destroyed, or to some thing of the tortfeasor whose market value is sufficient to finance the repair of the thing which the tortfeasor damaged
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Theft: if a person commits a property violation against another person by taking possession of some thing of his without his consent, then the victim becomes the owner of some thing of the tortfeasor which is equivalent to that of which the tortfeasor took possession
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Usurpation: if any person commits a property violation against another person, but this violation is neither damage, destruction, nor theft, then it is usurpation, and the victim obtains the right to use some thing owned by the tortfeasor in the same way that the tortfeasor used the thing owned by the victim
Causation:
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the action of a person is the cause of an occurrence if the action was a necessary condition for the occurrence, and if the person knew or reasonably should have known that the action would lead to the occurrence
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A person is the sole cause of all of his actions, except that if a person reasonably believes that he must take an action in order to avoid becoming the victim of some act of aggression with which he was threatened by another person, then that second person is the cause of the aforementioned action of the first person
III. Principle of Defense
Defense: if a person who reasonably believes that he must use violence against another person in order to avoid becoming the victim of the aggression with which that other person threatened him so uses violence, and only as necessary to prevent the aggression, then he is not the cause of this violence, but rather the other person is the cause
IV. Principle of Exchange
Property Exchange: an exchange of property occurs when both parties consent to the exchange
Consent: a person consents to an exchange of property when he intends for the proposed exchange to occur
Duress: a person who reasonably believes that he must indicate his consent to an exchange of property in order to avoid becoming the victim of the aggression with which he was threatened by another person is under duress and any indication of consent made by a person under duress is not evidence of consent
V. Principle of Homesteading
Unowned Property: unowned property is any thing which either has never been owned by any person, or which was owned by a person who has died without inheritors, or which was owned by a person who has voluntarily renounced ownership
Acquisition: the first person to use unowned property becomes the owner thereof, and if multiple persons begin to use the unowned property at the same time, then the person who has invested the most capital (measured in money units) into the property shall become the owner thereof