He is called Mitch (the theme), because his name is Mitchell (the rheme). – principal clause expresses the starting point, while the subordinate clause renders the main idea (the speaker’s explanation of the reason of “calling him Mitch”). 2. As his name is Mitchell (the theme), he is called Mitch (the rheme). – the informative roles will be re-shaped accordingly. One of the central problems concerning the complex sentences deals with the principles of classification of subordinate clauses. Within the traditional linguistics the 2 different principles have been put forward. The first is functional and the second is categorial.