This dissertation is a cross-sectional study of the acquisition of tense and aspect by 45 Persian speakers as the experimental group and 15 native English speaking children as the control group. This study specifically investigates the hypothesis of Primacy of Aspect (POA) that claims there is; (1) a strong association of past/perfective morpheme with achievement and accomplishment verbs, (2) a strong association of progressive morpheme with activity verbs, (3) no overextension of progressive inflection to stative verbs, and (4) strong association of the present morpheme '-s' with stative verbs. The study also argues for the semantic implications of the present data for the Distributional Bias Hypothesis (Andersen 1990), that the distinction of verb type in the input is skewed so as to create the acquisitional pattern found in studies of the POA in language acquisition, and for the Language Bioprogram (Bickerton 1981), that aspectual values are the knowledge a child is born with as the sources of the POA in SLA. The study also examines the syntactic implications of the data for the 'initial state' hypotheses in SLA: The Minimal Trees Hypothesis (Vainikka & Young-Scholten 1994, 1996a, 1996b), The Full Transfer/Full Access hypothesis (Schwartz & Sprouse 1996) and The Weak Parametric Transfer (Valueless Features) Hypothesis (Eubank 1993/94, 1996). The results supported the findings of the POA and the Minimal Trees Hypothesis.

This experimental study investigates the second language acquisition of the four Mandarin aspect markers -le, -guo, -zhe, and zai- by native Swedish university students enrolled in Chinese language courses in Sweden. The main points of inquiry are acquisition order, the Aspect Hypothesis, the Distributional Bias Hypothesis, and the Prototype Model. The study contains a cross-sectional study and a longitudinal study. Both written and spoken data are collected. The tasks in the cross-sectional study include film-retelling, picture-retelling, grammaticality judgment, fill-in-the-blank questions and comprehension. The longitudinal study includes written data produced by seven students in their tri-monthly journal. The study shows that perfective markers are produced before imperfective markers. The results of the experiments are consistent with the Aspect Hypothesis. The Distributional Bias Hypothesis can account for most of the Aspect Hypothesis but there are exceptions that indicate that other factors could also influence the acquisition process, such as L1 transfer. The Prototype Model cannot be conclusively proven. Apart from contributing to second-language acquisition theo-ries on cross-linguistic tense-aspect morphology, this study can provide empirical evidence with significant pedagogical implications for the second-language learning classroom.