Liberty is most broadly understood as some ‘absence of constraints’. Libertarians are interested in social or interpersonal liberty: people not being constrained by each other in the sense of proactively imposing or aggressing. Without such proactive constraints, it follows that people will immediately control (i.e., in effect own) themselves and any external goods they come to acquire without proactively imposing. Thus people have liberty to the extent that they are not proactively interfered with in their bodies or external property.
Various problems and paradoxes can be posed. For instance, can someone secretly buy all the land around you and then not let you out? Can light waves from a few electric lights on one’s own property ‘trespass’ on to others’ property without their permission? Such problem cases can be solved by reverting to the more abstract, pre-propertarian, theory of liberty. Where clashes of proactive impositions are inevitable among some people, the libertarian policy is to follow whichever rule will minimize such impositions. So, generally (but special cases might entail a different result from applying the principle), a right of access to one’s land and a right to have some lights without a blackout are the lesser impositions than their opposites.
What libertarians usually say about some other ideological conceptions of liberty is that they are not about interpersonal liberty at all, but rather about power, ability, opportunity, self-realization, or any number of other distinct things. However, it would be foolish to argue about the mere use of words and so if people want to define ‘liberty’ in some other way then let them. But the libertarian is advocating liberty only in, more or less, the sense explained.
Why should people have such liberty? It is a conjecture that this is desirable. It is better to criticize the conjecture in the critical rationalist manner than ask for supporting reasons. But it ought to be understood that libertarians typically also suppose that there is no systematic clash with human welfare. One can, of course, explain how libertarians think liberty will operate, and such explanations abound throughout this dictionary (such as, charity; free market; free trade; invisible hand; law), but an explanation is not a justification and it is itself conjectural. Most libertarians are benighted justificationists, like most people, and so they attempt to offer epistemological support for libertarianism by reference to apriorist Austrian economics, autonomy, contractarianism (see social contract), natural rights, utilitarianism, or whatever happens to be the latest justificationist fashion.
J.C. Lester has been published in various scholarly periodicals and books. He has taught at several university institutions, including the London School of Economics.