The biabsolutive construction in Lak and Tsez

In ergative constructions, the agent of a transitive verb is in the ergative case and the theme is in the absolutive case. By contrast, in biabsolutive constructions, both the agent and theme of a transitive verb appear in the absolutive case. This paper presents and analyzes the biabsolutive construction in two Nakh-Dagestanian languages, Lak and Tsez. Despite many surface similarities, the biabsolutive constructions in Lak and Tsez call for different syntactic analyses. We argue that the biabsolutive construction in Lak is an instance of restructuring in the presence of an aspectual head bearing a progressive (imperfective) feature. Tsez biabsolutive constructions, on the other hand, are biclausal; we argue that the theme and the lexical verb are contained in a PP complement selected by a light verb. Related languages may be classified as “Lak-type” or “Tsez-type” based on the behavior of their biabsolutives. The existence of two underlying structures for one surface pattern in Nakh-Dagestanian poses a learnability problem for a child acquiring a language with biabsolutive constructions. We outline a set of strategies used by a learner who must compare the available input data with a set of structural hypotheses.