The eminent sociolinguist William Labov once observed that there is no such thing as a single-style speaker. He was surely right; you don’t talk to your grandmaw the same way you talk to friends in a bar. But variety in language goes far beyond such choices; it is evident in ethnicity, age, sex, region, and many more ways of cutting up the human pie. Sociolinguists are interested in describing all that variation, but they have three lurking motivations. 1) Could that variation be described in mathematically principled ways? 2) Could there be some relationship between that variation and language change? 3) Could the principled nature of that variation be used to confront negative stereotypes about some language varieties? This presentation will show that the answer to all these possibilities is a resounding “Yes.”