This study explored the linguistic intuition of Japanese speakers when they judged the grammaticality of isolated simple bitransitive sentences. The role of the number of arguments and the manner of presenting sentences—whether or not the number of arguments increased across judgment trials—in determining the judged grammaticality was examined. Findings showed that the speakers tended to judge even sentences lacking arguments as grammatical. A direct object was most influential in determining judged grammaticality, an indirect object next most influential, and a subject least influential. The manner of presenting sentences had an almost negligible effect. The findings suggest that speakers' judgments of sentences are graded as contrasted to linguists' judgments. Osgood's Naturalness Principle of 1980 was interpreted as providing a good explanation for the findings.