This paper investigates use of ain't in a corpus of naturalistic speech from forty-two African-American Philadelphians. Use of ain't in past/perfective contexts where it varies with didn't is considered a unique feature of AAE. This use is compared in apparent time to uses of ain't in tense-aspect environments shared with other English varieties. Results show that past/perfective uses of ain't increased during the twentieth century while use in other contexts remained stable, supporting the hypothesis that past/perfective uses resulted from recent change. Generalized linear models for ain't in past/perfective and other contexts show that sociostylistic and linguistic constraints are otherwise the same across contexts. Finally, evidence that a past/perfective use of ain't resulted from either the phonetic reduction of didn't or a shift in meaning from uses of ain't in anterior contexts is examined.