The observation that different types of knowledge employ different types of expressions is probably universally valid. The concrete subdivisions of the semantic domain of knowledge, however, may be highly different among languages. Moreover, individual languages use very different strategies to form complement clauses. As propositional knowledge (know that) and procedural knowledge (know how) often concern events and activities, the semantic domain of knowledge and the syntactic domain of clausal complementation frequently interact. Taking these considerations as a starting point, the present paper investigates complementation strategies in Macedonian and Turkish, a Slavic and a Turkic language. Standard Macedonian and Standard Turkish possess highly dissimilar strategies for forming complement clauses. While Macedonian prefers finite complementation strategies, Standard Turkish generally uses verbal nouns, i.e. non-finite items, in clausal complementation. At the same time, the semantic domains of knowledge and possibility are organized very differently in these two languages as well. The paper identifies the similarities and differences between the Macedonian and Standard Turkish patterns of expression of knowledge and possibility and investigates the question of how language contact with Macedonian has influenced the expression types in the Turkish dialect of the town of Ohrid, where a Western Rumelian Turkish variety has been in longstanding intensive contact with Macedonian. The study will reveal a deep structural impact of Macedonian both on the semantic and the morphosyntactic design of the language system of the Turkish dialect of Ohrid.