Children acquire argument structure through distributional evidence, but how does this interacts with event semantics and existing verb knowledge? The current study compares verb learning in adult speakers of Japanese (where lexical causatives span wider semantic categories) and English (where alternation is more restricted). In the Fully alternating familiarization, internally caused events (similar to "descend") and externally caused events (similar to "rock") occurred with novel verbs in transitive and intransitive frames. In the Semi-alternating familiarization, internally caused events occurred with intransitives only while externally caused events occurred with both frames. During the test, participants rated the naturalness of transitive and intransitive descriptions for all events. For internally caused events, transitives were rated equivalently low across speakers after the Semi-alternating familiarization (which featured only intransitives), while intransitives were more felicitous for English compared to Japanese speakers. For externally caused events, all participants rated transitives higher than intransitives, despite equal occurrence across familiarizations. This may be related to the presence of salient animate agents in scenes. Together, this suggests that syntactic and semantic biases concurrently influence the interpretation of distributional evidence. Input statistics are interpreted through existing syntactic representations, and salient semantic distinctions may exert a bias for syntactic instantiations.