In recent years an increasing number of political philosophers have begun to ground their arguments in empirical evidence. I investigate this novel approach by way of example. The object of my case study is David Miller’s renewed empirical argument for a needs-based principle of justice. First, I introduce Miller’s argument. Then I raise four worries about the application of his methodology that give rise to corresponding general recommendations for how to do empirical political philosophy. Proponents of this approach should take (...) care to (1) check for inappropriately narrow (and broad) samples, (2) verify studies’ relevance for their empirical hypotheses, (3) adjust their confidence to the available empirical evidence, and (4) properly integrate their hypotheses into their philosophical theorizing. (shrink)