Theme-Rheme Structure in Clause Complexes of Persian Scientific Texts Based on SFG (Systemic Functional Grammar)

In the present article, theme-theme structure in clause-complexes of specialized texts (such as biochemistry, physics and anatomy) is studied based on SFG. At first, clause-complexes types in theme-theme structure of scientific texts are classified, and by describing and analyzing different types of clause-complexes (dependent/ dominant) it is revealed that these clauses are used more than simple ones within the whole corpus. Then, theme-theme structure is analyzed, and the result illustrates that clause analysis is possible at one, two or three layers at the same time, depending on the clause type. Therefore, one can find layers of themes in such clauses and introduce the notion of layer theme. Studying simple/complex themes revealed that in the scientific genre, complex themes are used more than textual ones. This is because the sequences of textual themes in the scientific texts are something usual. Complex clauses, complex themes and multiple layers of clause analysis indicate speech adjuncts in scientific texts, and consideration of such structural elements is effective in discourse organizing, text development and perception process. This is useful for text evaluation and can be considered as a criterion for transfer of information to the addressee, as it is seen in physics, biochemistry and anatomy texts respectively.