This article shows how a systematic impersonalization alternation in Russian provides additional evidence for underspecification in argument structure. In the case of a large class of lexically causative verbs, the causer is realized either as a volitional Agent in the nominative case or as an oblique-marked, nonvolitional causer, depending on how the event is construed. A causative theory of accusative is advanced, according to which the mere presence of external causation is a sufficient condition for accusative licensing, including those cases that lack an external argument altogether. The analysis is extended to explain accusative preservation in the Icelandic “fate accusative” construction
