Cross-linguistically, the existence of ‘double case’ configurations (e.g., nom-subject and nom-object) presents an empirical challenge to theories of case where anti-identity, or distinctness between two NPs, plays a key role (e.g., Yip, Maling & Jackendoff 1987). This study investigates the factors that influence the distribution of nominative object constructions in Korean. In a novel acceptability judgment experiment, we find that sentences with nom-objects are rated less acceptable than those with acc-objects. In a corpus survey, sentences with nom-objects commonly have topic-marked subjects. We propose the Morphological-Thematic-Grammatical (MTG) Alignment Hypothesis, which posits that sentences are maximally acceptable when there is maximal alignment between morphological case marking, thematic role, and grammatical function. In nom-acc constructions, this alignment is achieved because the highest-ranked subject (Keenan & Comrie 1977) is marked with highest-ranked nominative case (Otsuka 2006) and functions as a higher-ranked agent or experiencer. The lower-ranked object, meanwhile, has lower-ranked accusative case and functions as a lower-ranked patient. In contrast, nom-nom (and dat-nom) constructions fail to achieve this alignment. Our analysis treats the relevant constraints (e.g., distinctness, alignment) as interacting with each other to produce cumulative effects on acceptability.