Exchanges with and without the sword: slavery, politics-as-exchange and freedom in James M. Buchanan's institutional economics

James M. Buchanan's politics-as-exchange retrospectively conceptualized formal institutions emerging from bilateral agreements to establish reciprocal rights and prospectively guided constitutional entrepreneurs to broker Pareto-superior reforms that had unanimous consent. Buchanan believed this conceptualization of politics-as-exchange was necessitated by his ontological–methodological individualism and would initiate a new era of consensual politics, but it is argued it led to illiberal conclusions that reflected dissonance between his Kantian individualism and Humean subjectivism. It meant, for example, that slavery was characterized as a bilateral agreement between very unequal parties and it is argued it logically implied abolition required the consent of slaveowners. But Buchanan's ontology was compatible with the introduction into his framework of a right of exit that would have differentiated between exchanges with and without the sword to produce a consistent liberal constitutionalism.