Following Douglas and Kristeva, Sibley theorizes in Geographies of Exclusion that socio-spatial boundaries necessarily activate discourses of purity and impurity. Yet there is also a second, more sophisticated theory present in the text. Sibley offers three qualifications to Douglas and Kristeva, emphasizing the culturally specific nature of purity and impurity classifications, their status as contested and metaphorical discourses, and their irreducibly spatial organization and operation. Furthermore, beyond these qualifications, a close reading of the grain of Sibley’s argument suggests an account in which (a) temporal closeness to the origin and (b) spatial homogeneity are the standard against which "purity" is measured. Purity and impurity, then, would not attend any "matter out of place" but operate within particular cultural contexts as assessments of whether a phenomenon or space corresponds, in its relative homogeneity, to its impure origin and essence. This perspective offers support for addressing the materiality of purity and impurity discourses.