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.