Abstract：Abstract: Doctoral dissertation acknowledgements are rhetorical discourses, which enhance the construction of the writers’ academic credibility. Based on the self-built diachronic corpus, this research investigated the differences and diachronic changes in the ethical appeals, i.e. the construction of academic credibility from the aspects of authority and identity, between Chinese and English doctoral dissertation acknowledgements during the period from 2003 to 2013 in the areas of philosophy and humanities. The results showed that in the English acknowledgements there were more cases of ethical appeals to authority than in the Chinese ones while in the Chinese acknowledgements there were more appeals to identity. Moreover, in both Chinese and English acknowledgements, there were certain diachronic changes which demonstrated an increasing tendency in ethical appeals to authority and identity. The main reasons for these may lie in the differences between Chinese and foreign doctoral education models, languages themselves, and social cultures.
