The present paper is concerned with a historical puzzle: the changing position of the marker si in the extant Baltic languages, Lithuanian and Latvian. Si appears before the root in prefixed verbs and verb-finally in prefixless verbs in Lithuanian and dialectal Latvian, as opposed to a consistently verb-final position in standard Latvian and in Slavic languages, specifically Russian. This ordering is examined within a larger picture of morpheme linearization – focusing primarily on Lithuanian, but also bringing in Latvian and Latgalian data – to account for the Baltic paradigm. Historically a pronoun, si is argued to have incorporated into the verbal structure, and to maintain nowadays a binding relation with the subject of the sentence. The placement of si within the verb is shown to depend on two factors: the type of the antecedent and the morphosyntactic composition of the verb. The findings presented here also provide new evidence against the Lexicalist Hypothesis.
