The present study investigated the effects of instruction on the use of the definite article "the" by Japanese learners of English by implementing two instructional treatments that varied in the extent to which they emphasized identifiability and accessibility. One instructional treatment, referred to as the traditional (TR) treatment, emphasized the linguistic/semantic notion of identifiability in which "the" serves to identify the referent. The other instructional treatment, operationalized as a mental space (MS) treatment, emphasized the cognitive notion of accessibility whereby "the" serves to mark an access path to the referent. The purpose of the comparison was to assess which types of metalinguistic information might be most effective for helping L2 learners of English to understand specific definite article usages. Three computer-assisted language learning (CALL) lessons averaging from 1.5 to 2 hours each were given individually to 83 Japanese learners of English, 42 in the TR group and 41 in the MS group. Counterbalanced versions of an article test were administered as a pre-test (Time 1), an immediate post-test (Time 2), and a delayed post-test (Time 3). Both groups exhibited significant increases at Time 2, which were maintained at Time 3, while the between-group comparisons showed that the MS group significantly outperformed the TR group at both Times 2 and 3. The different treatments had differential effects depending on the article types, with the MS group performing especially well on the most difficult conceptual usages.