This thesis investigates how native and second language (L2) speakers establish temporal relations in Spanish, integrating formal linguistic theory with experimental evidence. Part I examines temporal interpretation in complex (two-clause) sentences such as Mary said that John was sick. In this so-called ‘past-under-past’ construction, John’s illness may be understood as simultaneous with or anterior to Mary’s report. Competing accounts have attributed the availability (or lack thereof) of these readings either to Grammatical Aspect, contrasting perfective and imperfective aspect forms in the embedded clause, or to Lexical Aspect, distinguishing between stative and eventive predicates. The studies reported in this part of the thesis provide a systematic experimental test of these accounts with adult native speakers of Spanish. This language explicitly marks perfective and imperfective aspect across both stative and eventive predicates, offering an optimal setting for disentangling the respective contribution of Grammatical and Lexical Aspect to temporal interpretation. Part II turns to L2 acquisition, investigating L1 English learners of Spanish. The experiments presented here conceptualise the acquisition task as the reassembly of perfective and imperfective features, and introduce temporal interpretation in complex sentences as a novel testing ground of the extent to which learners have acquired the ordering function of Grammatical Aspect. By assessing interpretation in both simple (one-clause) and complex sentences within the same participants, this work further examines learners’ ability to distinguish aspect meanings across syntactic structures, providing a comprehensive account of the challenges that Grammatical Aspect poses in L2 acquisition.
