Locke's Case for Toleration Built on Uncertain Knowledge

Locke's argument in A Letter Concerning Toleration draws directly on the empiricist epistemology he had just finished defending in the Essay Concerning Human Understanding: since no one's mind arrives certain of contested metaphysical truths, and coercion cannot in any case produce genuine inward belief, only persuasion by evidence and argument, the very method the Essay recommends, can rightly move a mind toward true religion, so civil punishment for wrong belief is both illegitimate and useless. Locke excluded Catholics, on the ground that loyalty to a foreign sovereign made political rather than religious sense to police, and atheists, on the ground that a promise sworn by someone who does not believe an oath is binding before God carries no real force, exclusions later readers have treated as the theory failing its own premises rather than as incidental detail. The argument nonetheless became one of the empiricist tradition's most consequential exports into practical politics: it supplied much of the vocabulary the framers of religious liberty clauses in the American colonies and, later, the United States Constitution drew on, translating a claim about the limits of what the mind can know into a claim about the limits of what the state may compel.