Active or descriptive: Textual activity and its dynamic changes of Ph.D. theses across disciplines

As an innovative and systematic genre in the academic community, Ph.D. theses have been heatedly researched in the field of English for Academic Purposes. Although research on the functional and formal features of Ph.D. theses has been abundant, their stylometric traits regarding textual activity have not been explored. Accordingly, this study explored the textual activity of Ph.D. theses and its dynamic changes across natural sciences, social sciences and humanities. A total of 150 Ph.D. theses (50 from each discipline) were analyzed, and the ܳ and ɖଶ values were calculated to determine the textual activity of theses as well as its dynamic changes with the progression of texts. The results showed that, although the theses were found to be active in general, significant differences across disciplines do exist, in that the theses in natural sciences and humanities were more active while those in social sciences were more likely to lean towards the descriptive mode. This study has implications for widening the scope of cross-disciplinary academic genre analyses from an innovative quantitative linguistic perspective.