The Logic of Inference of Thought Experiments in Political Philosophy

Thought experiments are widely used and widely criticised in political theory. This paper highlights important and largely unnoticed parallels between thought experiments and comparison in the natural and social sciences. This gives us a more precise language with which to assess the strengths and weaknesses of thought experiments. And it gives us powerful tools for improving them, by using ideas like internal and external validity, controlled comparison, omitted variable bias, interaction effects, spurious correlations, testable implications, and parsimony. Focusing on variables is the key. This helps me address longstanding debates about ‘weird’ and ‘wacky’ thought experiments. I do not wish to exaggerate the scientific parallels: there are important differences too. But the similarities raise fascinating questions about the links between political theory and political science, and between philosophy and science more generally.

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