This paper compares knowledge of the properties of the Spanish copulas ser and estar, both of which translate as 'to be', by three groups of speakers: a control group of Spanish monolinguals, a group of Spanish/English early bilinguals, and a group of advanced L2 Spanish speakers. Assuming that the difference between the copulas is aspectual in nature, the possible interpretation of the subject as generic is examined by means of a Truth Value Judgment Task. Furthermore, a Grammaticality Judgment Task looks at the type of predicate permitted by each of the copulas, including adjectives and participles. The performance of the early bilinguals was indistinguishable from that of the monolinguals. The late learners seemed to have mastered the distinction in the case of adjectives, but not in the case of participles. The results are discussed in view of current suggestions that interfaces between syntax and interpretation may be particularly hard to acquire (Sorace 2004).