Issues in property theory
What can be property?
The two major justifications given for original property, or the homestead principle, are effort and scarcity. John Locke emphasized effort, "mixing your labor" with an object, or clearing and cultivating virgin land. Benjamin Tucker preferred to look at the telos of property, i.e. What is the purpose of property? His answer: to solve the scarcity problem. Only when items are relatively scarce with respect to people's desires do they become property. For example, hunter-gatherers did not consider land to be property, since there was no shortage of land. Agrarian societies later made arable land property, as it was scarce. For something to be economically scarce it must necessarily have the exclusivity property—that use by one person excludes others from using it. These two justifications lead to different conclusions on what can be property. Intellectual property—incorporeal things like ideas, plans, orderings and arrangements (musical compositions, novels, computer programs)—are generally considered valid property to those who support an effort justification, but invalid to those who support a scarcity justification, since the things don't have the exclusivity property (however, those who support a scarcity justification may still support other "intellectual property" laws such as Copyright, as long as these are a subject of contract instead of government arbitration). Thus even ardent propertarians may disagree about IP. By either standard, one's body is one's property.
From some anarchist points of view, the validity of property depends on whether the "property right" requires enforcement by the state. Different forms of "property" require different amounts of enforcement: intellectual property requires a great deal of state intervention to enforce, ownership of distant physical property requires quite a lot, ownership of carried objects requires very little, while ownership of one's own body requires absolutely no state intervention. Some anarchists don't believe in property at all.
Many things have existed that did not have an owner, sometimes called the commons. The term "commons," however, is also often used to mean something quite different: "general collective ownership"—i.e. common ownership. Also, the same term is sometimes used by statists to mean government-owned property that the general public is allowed to access (public property). Law in all societies has tended to develop towards reducing the number of things not having clear owners. Supporters of property rights argue that this enables better protection of scarce resources, due to the tragedy of the commons, while critics argue that it leads to the 'exploitation' of those resources for personal gain and that it hinders taking advantage of potential network effects. These arguments have differing validity for different types of "property"—things that are not scarce are, for instance, not subject to the tragedy of the commons. Some apparent critics advocate general collective ownership rather than ownerlessness.
Things that do not have owners include: ideas (except for intellectual property), seawater (which is, however, protected by anti-pollution laws), parts of the seafloor (see the United Nations Convention on the Law of the Sea for restrictions), gases in Earth's atmosphere, animals in the wild (although in most nations, animals are tied to the land. In the United States and Canada wildlife are generally defined in statute as property of the state. This public ownership of wildlife is referred to as the North American Model of Wildlife Conservation and is based on The Public Trust Doctrine.), celestial bodies and outer space, and land in Antarctica.
The nature of children under the age of majority is another contested issue here. In ancient societies children were generally considered the property of their parents. Children in most modern societies theoretically own their own bodies but are not considered competent to exercise their rights, and their parents or guardians are given most of the actual rights of control over them.
Questions regarding the nature of ownership of the body also come up in the issue of abortion, drugs and euthanasia.
In many ancient legal systems (e.g. early Roman law), religious sites (e.g. temples) were considered property of the God or gods they were devoted to. However, religious pluralism makes it more convenient to have religious sites owned by the religious body that runs them.
Intellectual property and air (airspace, no-fly zone, pollution laws, which can include tradable emissions rights) can be property in some senses of the word.
Ownership of land can be held separately from the ownership of rights over that land, including sporting rights, mineral rights, development rights, air rights, and such other rights as may be worth segregating from simple land ownership.
Who can be an owner?
Ownership laws may vary widely among countries depending on the nature of the property of interest (e.g. firearms, real property, personal property, animals). Persons can own property directly. In most societies legal entities, such as corporations, trusts and nations (or governments) own property.
In many countries women have limited access to property following restrictive inheritance and family laws, under which only men have actual or formal rights to own property.
In the Inca empire, the dead emperors, who were considered gods, still controlled property after death.
Whether and to what extent the state may interfere with property
Under United States law the principal limitations on whether and the extent to which the State may interfere with property rights are set by the Constitution. The "Takings" clause requires that the government (whether state or federal—for the 14th Amendment's due process clause imposes the 5th Amendment's takings clause on state governments) may take private property only for a public purpose, after exercising due process of law, and upon making "just compensation." If an interest is not deemed a "property" right or the conduct is merely an intentional tort, these limitations do not apply and the doctrine of sovereign immunity precludes relief. Moreover, if the interference does not almost completely make the property valueless, the interference will not be deemed a taking but instead a mere regulation of use. On the other hand, some governmental regulations of property use have been deemed so severe that they have been considered "regulatory takings." Moreover, conduct sometimes deemed only a nuisance or other tort has been held a taking of property where the conduct was sufficiently persistent and severe.