本文討論近代漢語無主語「被」字句的相關問題，以《朱子語類》作為主要的觀察對象，旁及其他近代文獻和現代漢語方言。研究發現「被」字句確實有某些例子在句法形式上缺乏主語，但在語義層次仍有假定言者主語的必要，顯示「被」具有「主觀化」的特性。此時「被」的語義仍帶有不由自主，莫可抗拒的意味。「被」兼表原因的用法不見得由無主語句演化而來，很可能是循著另一條語法化的道路，其發展過程先後經歷了「語用推理」和「語境吸收」兩種機制的運作。過去許多學者將表原因的「被」分析為介詞或連詞，本文藉由「被」的句法表現及語義特性，指出「被」仍具有動詞的特點。文末談論無主語「被」字句的歷時發展，並推測其衰微之因或許和「被」字句在北方話中不再是常用的口語形式有關。最後描述現代方言無主語被動式的南北差異，藉此說明各類被動表述的類型特色。

This study addressed the null-subject bei-construction in Modem Mandarin mainly based on "Zhuzi Yulei". Other related literature of Modem Chinese and dialects were also taken into analysis. The results showed the subjectification of bei. For some sentences, despite the fact that null subjects could be found from the syntactic surface structure, speaker subjects should be assumed at the semantic level. This showed that bei still conveyed that the subject can not prevent the action from happening.The null-subject sentences may not directly lead to the fact that bei could be used to give the reason for something. It may be resulted from grammaticalization in other ways. The developmental process involved two mechanisms, respectively pragmatic inference and absorption of context. Researchers in the past classify the reason-giving bei as a preposition or a conjunction, but this study argues that bei carries the characteristics of a verb according to the syntactic and semantic features of it.The study also discusses the diachronic development of the sentences with bei that involve the ellipsis of the subject. Presumably, the decreasing of such usage should be related to the fact that this usage is no longer a commonly used oral expression in northern dialects. This study finally reveals the features of different types of passive tenses by comparing the differences between the sentences with bei in northern dialects and those in southern dialects.