In the proposed study of languages ​​with different systems, a comparative analysis of cases of the Russian and Uzbek languages ​​is performed. The main result of our study is the definition of allomorphism and isomorphism of reliable systems of the Russian and Uzbek languages, which is based on the syntactic form of control of three-actant verbs in the Russian and Uzbek languages. Case meaning is understood as a generalization of the semantics of the actant designated by the studied case within the framework of Porzig's syntagmatic field. Porzig's syntagmatic field is specified by: a) a singular situation, which is designated by a predicative phrase containing predicate forms (finite verb) and actants of the predicate (for three-actant verbs - a subject and two objects); b) a class of situations that are designated by a syntactic construction, where each symbol denotes a class of verbs or a class of actants.