This paper examines the phonological leveling and diffusion of variants of /t/ in Liverpool, northwest England, and two localities in its hinterland. We show that lenited realizations of /t/, thought to be historically restricted to Liverpool, are increasing over time and spreading over geographical space. We explore Labov's (2007) claims that linguistic changes that progress via transmission, within a speech community, are reproduced in all their structural complexity, whereas changes that spread across speech communities, via diffusion, are “simplified” en route. We find support for these hypotheses. Using a comparative sociolinguistic methodology, we show that the linguistic constraints operating on the realization of /t/ as [h] in Liverpool have remained stable over time, while those in a nearby town—Skelmersdale—seem to have simplified. However, we show that not all speakers from Skelmersdale share the same constraints on this variable form, and we connect this with speakers' positive or negative attitudes toward Skelmersdale or Liverpool.