The paper is concerned with kako and če as two possibilities to introduce declarative complement clauses in pre-standardized Balkan Slavic writing. Comparing the usage of both in Sofronij Vračanski’s Nedelnik, his autobiography (both early 19th century) and a later edition of the Nedelnik (late 19th century) with their usage in 17th century damaskini, synchronic and diachronic evidence is provided that the variation between kako and če gradually becomes functionalised. This can be inferred from word order patterns that serve the syntactic and semantic integration of matrix and complement clause and the structuring of information. Based on these observations, the exclusive usage of kako in Sofronij’s autobiography can be accounted for in terms of the matching of linguistic function and genre requirements. The observed interactions between syntax, text and genre indicate a close interaction of linguistic and literary development in pre-standardized Balkan Slavic.