Vestigial ergativity in Shughni: At the intersection of alignment, clitic doubling, and feature-driven movement

This paper provides an account of two related aspects of the past-tense morphosyntax of Shughni (Eastern Iranian): (i) the use of second-position clitics, rather than the verbal suffixes of the present tense, to index past-tense subjects' phi-features; and (ii) a curious alignment pattern - sometimes referred to as vestigial ergativity - in which third-singular subjects of transitive and unergative verbs, but not unaccusative verbs, trigger a second-position clitic matched to their phi-features. After applying a battery of diagnostics to the Shughni clitics, I argue that these morphemes are the result of a clitic-doubling operation rather than agreement proper. A significant clue for this conclusion is the lack of any morphological material co-indexing third-singular unaccusative subjects, which I take to indicate that the past-tense clitics, unlike the present-tense suffixes, lack a default morpheme. This account not only provides support for the validity of diagnostics developed by previous authors for object clitics, but also highlights the importance of including subject clitics when developing a theory of clitic doubling and agreement. In the latter part of the paper, I build upon recent work on the alignment system of Davani (Western Iranian) to provide a feature-driven movement account of Shughni syntax, whereby all unaccusative subjects except third-singular move to a phase edge, where they are found by a probe on T-0 and trigger a second-position clitic bearing their phi-features.