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.