Locke argues mixing one's labor with unowned natural resources creates legitimate title prior to government. By working land or improving it, you acquire property rights. This labor theory justifies private property without appeals to contract or state grant, though it requires that 'enough and as good' remains for others and property not be wasted.
From your study of Locke and natural rights you know that Locke grounds political authority in the natural condition of human beings — free, equal, and subject to the natural law of reason, not to any government's edict. His labor theory of property extends this: property rights also originate in nature, prior to any civil institution. You do not have your property because a king granted it or a constitution protects it; you have it because you earned it through your own effort on what no one else owned.
The argument's core move is the labor-mixing thesis. Each person owns themselves and, therefore, owns the labor of their body and hands. When you apply your labor to unowned natural resources — clearing land, cultivating soil, carving wood — you extend the boundary of self-ownership into the external world. The object becomes yours because it has absorbed your effort, which was yours to begin with. Locke illustrates this with an acorn: if you pick up an acorn from the forest floor and carry it home, it becomes yours the moment you exert the effort to take it; you don't need anyone's permission.
This argument has a powerful intuitive pull, but Locke immediately recognizes it needs constraints. Unlimited appropriation would leave latecomers nothing. He introduces the Lockean Proviso: original acquisition is legitimate only if it leaves "enough, and as good" for others. The proviso functions as a side constraint on the labor-mixing principle. Locke was also insistent that property cannot accumulate beyond what one can use before it spoils — hence the spoilage limitation. The invention of money, however, dissolves this limit: money doesn't rot, so people can legitimately store value indefinitely by converting perishable goods into durable currency. Locke presents this as a tacit consent to unequal property accumulation.
The philosophical strengths and weaknesses of the theory come into focus when you press the labor-mixing metaphor. Robert Nozick famously asked: if I pour my can of tomato juice into the ocean, do I thereby own the ocean — or merely lose my tomato juice? The point is that "mixing labor" is a metaphor, not a precise criterion. What counts as sufficient labor to confer title? Why does mixing labor with a thing make the thing yours rather than simply diminishing your labor? These questions matter because the theory is doing a lot of political work: it is supposed to explain why existing distributions of land and property are (or could be) legitimate without appeal to government authority.
The downstream implications are substantial. Nozick builds an entire libertarian political philosophy on Lockean foundations, using it to argue that redistributive taxation violates property rights as robust as the right against theft. Egalitarian critics like G.A. Cohen reply that the original Lockean Proviso is almost certainly violated in any modern economy — the poor have not been left with "enough and as good" — which undermines the legitimacy of current property distributions. Your upcoming study of property and distributive justice will place this theory in direct confrontation with Rawlsian arguments: Rawls denies that natural talents or the accident of birth create strong property entitlements, while Locke-derived libertarians insist that self-ownership grounds property rights prior to any social arrangement.
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