The aim of the study is to identify the role of the postposition in the construction of divisible sentences based on the material of one of the Mordovian languages, Erzya. The paper presents the semantic and syntactic meaning of this auxiliary part of speech expressing various relationships between words. By forming a word form, it develops, complements or enhances the lexico-grammatical meaning of the word, becoming a member of the sentence along with it. The study is novel in that it is the first in Mordovian linguistics to describe in detail the role of the postposition, which syntactically connects sentence members and differentiates the meanings of word forms in phrases and sentences. As a result, it is revealed that the postposition influences the differentiation of the semantics of sentence members; it is indicated that the words of this auxiliary part of speech are divided into postpositions and postpositional words according to their origin and morphological composition; it is found that the postpositional constructions (adverbial and nominal) preserving the lexico-semantic meanings of the words from which they are formed are largely characterised by syncretism; it is noted that the meanings of case-postpositional forms are determined in the sentence.