Locke is read now for two things that look separate and are not. He argued that the mind starts empty and fills from experience, and he argued that political authority comes from the consent of the governed and can be withdrawn. Almost every assumption an ordinary person holds about where government gets its right to act traces through him.

The connection between the two arguments is the interesting part. If nobody is born knowing, then nobody is born knowing better, and the claim that some people are naturally fit to rule others loses the ground it had been standing on for a thousand years.

The problem

Locke's working life ran through the English Civil War, the execution of a king, a restoration, the Exclusion Crisis, five years of exile in Holland, and the Glorious Revolution. He was physician and political confidant to the Earl of Shaftesbury, which is why the exile happened.

The problem that period sets is not abstract. If inherited authority is not the answer, what is? Divine right had been the standing account of why anybody gets to command anybody, and it had just been shot to pieces in public. Something had to replace it, and the replacement had to work for people who disagreed with each other about God — because the alternative, as everyone involved had recently watched, was another war.

Locke's answer is that authority is constructed, by agreement, for a purpose, and it is bounded by the purpose.

The Second Treatise begins where such arguments conventionally begin, with people outside any government, and then does something unconventional with it.

Locke's state of nature is not Hobbes's war of all against all. It is tolerable — people have rights, there is a natural law, most of the time things work. What is missing is not order but a judge. In a dispute, each party judges its own case, and people are bad at that. Government exists to supply an impartial arbiter, and that is the whole of its warrant.

Two things follow, and they are the reason the argument was dangerous.

Because government exists for that purpose, it may do only what the purpose requires. A government that starts doing other things is not exceeding good manners; it is acting without authority.

And because authority came from the governed, it can go back to them. Locke is explicit that a government which systematically violates the rights it was constituted to protect has dissolved itself, and what follows is not rebellion against a legitimate power but resistance to a usurper. He was writing in the 1680s. This was not a thought experiment.

Property, which is the load-bearing argument

The famous chapter is the one where the trouble starts. The earth is given to everyone in common; a man owns himself; therefore when he mixes his labor with something unowned, it becomes his, without anyone's permission being required.

This is doing enormous work. It grounds private property without a sovereign grant, which is precisely what a theory hostile to inherited authority needs. It also comes with two limits that Locke states and then quietly loosens: take no more than you can use before it spoils, and leave enough and as good for others. Money, he observes, lets the first limit be evaded without waste, since gold does not rot. The second limit is met, he says, because there is still America.

Both moves are contestable and both were contested. But notice what the structure achieves: property, on this account, is prior to government rather than created by it, which means government cannot simply take it. That is the sentence the eighteenth century actually used.

Toleration, and its edges

The Letter Concerning Toleration makes an argument that is narrower than it is usually remembered as being, and stronger for it.

Locke does not argue that religious truth does not matter. He argues that force cannot produce belief. The magistrate can compel attendance and compel profession; he cannot compel the inward assent that would make either of them worth anything. So coercion in religion is not merely cruel, it is incompetent — it cannot achieve the end it claims.

The limits are where a modern reader stops short. Catholics are excluded, because they owe allegiance to a foreign prince. Atheists are excluded, because an oath means nothing to a man who fears no God, and a society running on oaths cannot admit them. Both exclusions are consistent with the argument as Locke built it — his case is about civil order, not about conscience as such — and both show how much of the modern doctrine he did not hold.

The objection

Locke wrote that no man may be subjected to the arbitrary power of another. He also drafted the Fundamental Constitutions of Carolina, which gave every freeman absolute power over his slaves, held stock in the Royal African Company, and served on the Board of Trade administering colonial policy.

There is no reading on which this is a small discrepancy, and the attempts to dissolve it are unconvincing in both directions. The claim that his natural law simply did not extend to Africans has to be argued rather than assumed, since the text does not say so. The claim that the theory is unaffected because the man was inconsistent is too easy, because the property argument — labor mixed with unowned land, and there is still America — is the same argument that was being used to justify what was happening in the Carolinas, by the man who wrote both.

The honest version is that the theory is more available to that use than its admirers like, and that reading it with the Carolinas in view is a better test of it than reading it without.

Where to go next

The epistemology is argued in full on the book's own page: An Essay Concerning Human Understanding. For the mind-starts-empty claim on its own, tabula rasa; for the memory account of the self, personal identity. Hume is what happens when the same starting point is applied without Locke's willingness to stop.