In spoken Chinese,'suoyi(所以)'is used as a conjunction of result or a discourse marker.The usage of'suoyi(所以)'is complex in spoken Chinese,which documents the multiple grammatical,textual,interactional roles in conversation.This paper also discusses the distribution of'suoyi(所以)'in spoken and written Chinese.We found the difference in frequency of'suoyi(所以)'in this two genres is very significant,and we maintain that its semantic reduction and function expansion in spoken Chi...