Through a series of studies, this thesis investigates the learning of definiteness in Russian-speaking students of Swedish. A communicative oral-production task elicited modified and non-modified noun phrases in indefinite and definite contexts. Study I describes the development of the morphosyntactic structure through which Swedish encodes definiteness, the association between this structure and its meaning, and the relationship between those two tasks over time. Using an English version of the elicitation task and a test of metalinguistic knowledge, Study II examines the relationship between the learners’ explicit knowledge of article semantics and their actual use of English articles. Adding a test of language-learning aptitude, Study III then explores both the influence of second-language English and that of aptitude on the development of Swedish. Finally, Study IV discusses the role of complexity and input frequency. 

The main findings include that, at the onset of Swedish study, the learners had minimal knowledge of the morphosyntactic structure but were generally sensitive to the meaning of definiteness. However, knowledge of form developed over time while knowledge of meaning did not, and the two learning tasks did not appear to be directly related to each other. In addition, the learners were seldom aware that choosing between indefinite and definite articles requires the speaker to take the hearer’s perspective, but this lack of metalinguistic understanding did not seem to affect their use of articles. Further, previous knowledge of English appeared to facilitate the development of a Swedish morpheme that is structurally similar to its English counterpart, while aptitude was associated with the development of a morpheme whose English counterpart is structurally different. Finally, the learners used high-frequency morphemes more consistently than low-frequency ones, and morphemes were more likely to be supplied in frequent constructions than in infrequent ones. These findings are discussed in relation to a modular, cognitive framework for language learning and use.