A politician gives a TV interview on the topic of immigration, an issue of crucial importance to voters. The interviewer probes some of the politician’s claims about why certain migrants are leaving their home countries: is it mainly political crisis, or is it the pull of jobs? They also discuss the impact of migration: will it buffer or burden the local welfare state? Each tries to cite some evidence in favor of their view, such as anecdotes about why certain people chose to migrate. Sociologists, economists, geographers, and so on try to answer these questions more rigorously and systematically: they compile larger quantities of data, and they attempt to build sophisticated theories to make sense of the data. We might call these “empirical” disciplines: those concerning what happens and why.