“Illegal alien,” as a category of analysis, should be understood primarily as a discursive formation, yet the emergence and spread of the category in public debate cannot be explained by its discursive qualities. Failing to see this has analytical consequences: it results in a constant sidetracking of the question of why illegality itself came to be a central issue, and in a reification of the category. This paper is intended as a methodological intervention aimed at solving these issues. The first part illustrates the absence of a strict legalistic basis for the category, and reviews key works that fail to incorporate this into their conceptual design. The second part, contrasts two periods of time in U.S. political debate – the mid-2000s when the category was dominant, and the 1930s when the category, albeit pushed by elites, failed to become central- suggesting the need for a discursive analysis that goes beyond discourse.