Variation within the Spanish Imperfective domain partially responds to the Progressive-to-Imperfective diachronic shift (Dahl 1985, Bybee et al. 1994). Spanish had originally only one imperfective marker (the Simple Present (PRES)) that expressed both habitual and event-in-progress readings, until it developed a Present Progressive marker (PROG) to express the event-in-progress reading (emergence stage). Over time, these markers became restricted to mutually exclusive readings (categoricalization stage): PRES for habituals; PROG for events-in-progress. This stage is expected to last until PROG gets reanalyzed as a general imperfectivity marker (generalization stage), becoming the only device to express both readings (Deo 2015).

Through acceptability judgment tasks (n=232) across different Spanish dialects (Central Peninsular, Mexican Altiplano, and Rioplatense), I have shown that these stages are not so clear-cut: Contemporary Spanish is between a categoricalization and a generalization stage. Some specific contexts allow PRES to still express an event-in-progress, while other specific contexts allow PROG to already express a habitual reading. Specifically, I show that PRES can convey an event-in-progress only when speaker and hearer share perceptual access to the relevant event. Conversely, PROG can be used regardless of the kind of contextual information that accompanies the marker. On the other hand, my work shows that while PRES can convey a habitual reading in any communicative situation, PROG can only do so when the presupposition associated with its auxiliary verb, estar –which requires the construal of alternative situations at which the proposition does not hold (e.g., Sánchez Alonso et al. 2017)– is satisfied by contextual information. Two Self-Paced-Reading studies (n=300) further show that these contextual modulations are observable during real-time comprehension, following expected patterns: less acceptable context-marker combinations produce longer reading times than more acceptable ones.

Moreover, these contextual constraints are at play in different ways across different dialectal varieties. In the case of the event-in-progress reading, when shared perceptual access is provided by the context, PRES is acceptable in Rioplatense and Central Peninsular Spanish, but in Mexican Altiplano Spanish participants only accept PROG. For the habitual reading, when context satisfies the presuppositional component of the auxiliary verb, PROG can be used in Rioplatense and Central Peninsular Spanish, while in Mexican Altiplano Spanish, PROG is no longer dependent on contextual support. This pattern is consistent with a generalization process already underway in the three varieties, with the Mexican variety further along the grammaticalization path from Progressive-to-Imperfective. Altogether, these cross-dialectal patterns are consistent with a model of variation and change visible through offline and online experimental methods, and subject to identifiable contextual factors.