The word “libertarian” has a twisting history. In nineteenth-century France, libertaire was used by anarchist communists, and in much of the world libertarian socialism still means anarchism. In the United States from the mid-twentieth century, however, “libertarian” came to mean a defender of individual liberty, private property and free markets who wants government kept small. This level follows that second tradition to its roots.
Locke's foundations
John Locke's Second Treatise of Government (1689) supplied ideas libertarians still use. Before government, he argued, people live in a state of nature governed by a moral law that forbids harming others in their “life, health, liberty, or possessions.” Each person has natural rights, and “every man has a property in his own person.”
Locke explained how private property can arise from things no one owns: when you mix your labor with unowned land or materials, you make them yours. He added a limit, now called the Lockean proviso: the appropriation is legitimate where there is “enough, and as good, left in common for others.” Government is created by consent to protect these rights, and a government that violates them may be resisted. Locke himself was not a libertarian in the modern sense; he accepted majority rule and taxation approved by representatives.
Mill's harm principle
In On Liberty (1859), John Stuart Mill argued that “the only purpose for which power can be rightfully exercised over any member of a civilised community, against his will, is to prevent harm to others.” This harm principle is a favorite libertarian tool for opposing laws against private conduct. Mill was not a libertarian either: he supported compulsory education and was sympathetic to workers' cooperatives.
Nozick's minimal state
The most influential philosophical defense of libertarianism is Robert Nozick's Anarchy, State, and Utopia (1974). Nozick began from strong individual rights, which work as side constraints: others may not violate them even to achieve good results overall.
He defended a minimal state, sometimes called the night-watchman state, limited to protecting people against force, theft and fraud and enforcing contracts. Anything more extensive, he argued, violates rights. Against anarchists, Nozick argued that a minimal state could arise without violating anyone's rights: people would join private protective associations, one would become dominant in each area, and that dominant association would become a minimal state.
Entitlement theory
Nozick's account of fair distribution is the entitlement theory. A person's holdings are just if they came about through three principles: justice in acquisition (how unowned things first become owned), justice in transfer (voluntary exchange and gift), and rectification of past injustices. Justice is historical: it depends on how a distribution came about, not on whether it matches a pattern such as equality.
His best known illustration features the basketball star Wilt Chamberlain. Start with whatever distribution you think is just. Now a million fans each freely pay twenty-five cents to watch Chamberlain play, and he ends up far richer than anyone else. Each step was voluntary, so how can the result be unjust? Nozick's lesson: free choices continually upset any pattern, so maintaining one requires continual interference in people's lives. He went further, arguing that taxing earnings from labor is comparable to forced labor.
Self-ownership
Underlying all this is the idea of self-ownership: each person has rights over their own body, labor and talents much like an owner's rights over property. Critics, discussed later, ask whether self-ownership really supports unlimited ownership of the outside world.
Worked example: the island settlement
Imagine an uninhabited island settled by a hundred families. Use Nozick's three principles to judge who owns what fifty years later.
Justice in acquisition. The first settlers fenced and farmed plots. By Locke's test, mixing labor with unowned land made it theirs. But suppose one family fenced the only freshwater spring. The Lockean proviso asks whether enough and as good was left for others. Without the spring, it was not, so that claim is suspect.
Justice in transfer. Over the years, families traded land, sold produce and left property to their children. A fisherman who built better boats grew rich because others freely bought his catch. On Nozick's view his wealth is just, however unequal the result, because each step was voluntary.
Rectification. Suppose that in the tenth year a group drove three families off their farms by threats. Their descendants are now poorer. Nozick holds that past injustice must be corrected, perhaps by returning land or paying compensation. Critics note that in the real world, where centuries of conquest and theft shaped who owns what, rectification could demand large transfers, possibly more than many egalitarians would ask.
Notice what Nozick does not ask: whether the final distribution is equal, or whether the poorest are as well off as possible. For him those questions miss the point. The question is how holdings came about. That is exactly what his critics dispute, and it leads to the debates in the next level.