In this paper, I argue that filled pause selection (um/uh) is a sociolinguistic variable, conditioned by both internal and external factors. There appears to be a language change in progress towards selecting um more often than uh. In all respects, the (UHM) variable appears to pattern quantiatively just like all other sociolinguistic variables which have been examined, even though the locus of (UHM) variation would seem to be firmly in the speech planning domain. Combined with the quantitative systematicity of sociolinguistic variables across the full range of linguistic modules, I argue that the locus of variation may not be in the grammar, but rather constitutes a separate domain of knowledge, perhaps what Preston (2004) called the “sociocultural selection device.”