I apply the theoretical account of clause combining developed earlier based on Ossetic data to Russian causal clauses. Three Russian subordinating conjunctions are analyzed: potomu čto ‘because’, poskolʼku ‘since’ and tak kak ‘for’. I show that the coordinating/subordinating properties of all three are different. The conjunction textitpotomu čto is limited in its linear ordering and can be treated as involving a flat constituent structure. At the same time, textitposkol’ku and textittak kak allow comparatively free embedding in the matrix clause and preposition, which speaks in favour of subordination. However, other properties of these subordinators do not align with their linear order properties: all three are subordinating according to the Coordinate Structure Constraint and scope of mood and other syntactic operators. The conjunctions also have semantic differences: textittak kak is closer to coordination, while textitposkol’ku and textitpotomu čto are closer to subordination. Therefore, an adequate account of Russian data requires reference to three levels of language structure: constituent structure, functional structure and semantics.