The paper presents a contrastive analysis of the possibilities of forming inchoative verbs from state predicates in Bulgarian and Russian. The derivational patterns under consideration are much more productive in Bulgarian, but the aspectual properties of predicates impose significant constraints on their combinability with inchoative prefixes in both languages. The possibility of forming an inchoative verb can serve as a reliable diagnostic of a predicate’s membership to a particular ontological category within the semantic typology of predicates.