This dissertation investigates the use of ain’t for negation in past tense contexts in Philadelphia African American English [PhAAE]. This use of ain’t, which varies with didn’t, is a unique feature of AAE (Labov et al. 1968) and has implications for the expression of tense/aspect in the language. First, it further levels tense/aspect cues from auxiliaries in negative contexts. Second, whereas verbal complements of didn’t are uninflected (1a), complements of ain’t may either be uninflected or in preterit form (1b). This asymmetry indicates potential structural differences between ain’t and didn’t. (1) a. They didn’t play yesterday. b. They ain’t play(ed) yesterday. Consequently, this dissertation joins a quantitative study of the social and linguistic factors conditioning use of ain’t with a distributional investigation of its syntax and interaction with tense morphology. Toward that end, I analyze naturalistic speech data from 42 speakers in a corpus of casual conversations collected in the early 1980s from African American Philadelphians. First, analysis of social conditioning on variation between ain’t and didn’t reveals that the use of ain’t in this context is a recent innovation tied to the social setting of urban Northern cities like Philadelphia. Second, an investigation of following verbal morphology indicates that the construction ain’t+base is preferred to ain’t+preterit (used only 25% of the time). Apparent time analysis reveals that ain’t+preterit is preferred by older speakers, suggesting that it may be an older construction. In combination with an analysis of linguistic conditioning on use of ain’t, specifically verbal stativy, I argue that past tense ain’t was reanalyzed from present perfect ain’t, which varies with haven’t and has the same form (2). (2) They ain’t played since Monday. “They haven’t played since Monday.” Based on these results as well as an examination of past vs. perfect constructions and associated verbal forms in PhAAE, I consider the hypothesis that inflection is generated in a functional head lower than tense in ain’t+preterit constructions. Consequently, this dissertation demonstrates a difference in structure between ain’t and didn’t sentences and a distinction in the grammar of AAE compared to other varieties of English.