The concept of the complex sentence element (clause) is anchored in the formalsemantic level description. This description follows up on the classical approach, from form to meaning, but is based on K. Svoboda’s original concept of the complex sentence, among others. The concept of the complex sentence element on the level of complex sentence elements corresponds to the concept of the verbal clause as a complex unit on the lower sentence-element level. Like in phonology, certain traits, namely those of the complex sentence elements, are delimited as binary oppositions: subordinating – coordinating connective, incorporation by determination or apposition – disincorporation by coordination or parenthesis, commenting – lack of commenting. The focus of the article lies in the classification of complex sentence elements into nine types based on the combinations of the traits mentioned above. In one center of the system of these elements, there is a traditional subordinate clause, the subordinate clause with restricted determination, semi-subordinate clause, and false subordinate clause stand further from it. The second center is formed by the traditional main clause, to which the main clause with restricted coordination and the main clause with determination are attached. The periphery of the system is formed by the oppositional subordinate and appositional coordinate clause.