1 Reconstructing the Source of Nominative-Absolutive Alignment in Two Amazonian Language Families Spike Gildea Flávia de Castro Alves University of Oregon Universidade de Brasília Collegium de Lyon Abstract In this paper, we take the strong position that syntactic constructions can be reconstructed, first by identifying constructional cognates, then by identifying evidence for the directionality of constructional change that best explains the modern distribution of the cognate constructions from the hypothesized source construction. Further, we argue that the grammatical properties of the resultant constructions are often best explained by a combination of their etymological source(s) and the evolutionary pathways by which they arise. We illustrate these larger theoretical claims by reconstructing a typologically unusual set of constructions in the Jê and Cariban families, which present a rare ergative alignment pattern we call nominative- absolutive. This alignment pattern, with nominative dependent-marking and absolutive verbal indexation, was held to be impossible prior to 2010, and remains attested in very few language families. In the Jê and Cariban languages, this alignment type always occurs as part of ergative splits conditioned by TAM, which are again counter to previously held universals in that they are conditioned by future tense, imperfective aspects, and agent-oriented modalities. We reconstruct the sources of these nominative-absolutive constructions and then argue that the unusual formal properties and functional distributions of the nominative-absolutive clause types are both best understood as combinations of typologically unusual source constructions that follow well- established diachronic pathways of tense-aspect-mood renewal.