This study deals with the so-called Light Verb Construction in Japanese, which consists of the verb suru do and an accusative (o) marked verbal noun (VN). There have been unresolved debates on the role of suru: whether suru in VN-o suru functions as a light or heavy verb. The previous studies attempt to disambiguate VN-o suru formations by relying solely on examining whether suru can be thematically light or not. This study argues that the ambiguity does not stem from the weight of suru but from its accusative phrase: whether it is headed by a thematic (complex event) VN or non-thematic (simple event) VN. Using a principles and parameters approach and employing ideas from conceptual semantics and theories of aspect, this study demonstrates that the characterization of VN-o suru formations arises not from the dichotic behavior of suru but from the dichotic behavior of the accusative phrase.