This study aims to examine the wider use of ‘tae-mun’ causative expressions diachronically and their discourse features in modern Korean conversation. For this purpose, discourse analysis method is applied to corpus data arranged from 19c 20c novels, dramas, movies and talk show progra. The results of this study presents : (1) ‘tae-mun’ has begun to be used as a connective expression from the end of 19c with other causative expressions like ‘ka-dak’ and ‘jon-cha’ and in the early of 20c, ‘tae-mun’ has been used as a sentence ending expression at the same time. (2) ‘tae-mun’ expressions has syntactic restricts rarely and it makes the wider use of ‘tae-mun’. (3) Through analyzing the discourse data, the interactive functions of ‘tae-mun’ are analyzed in terms of two big categories of [reason] and [justification] in spoken discourse context. These basic discourse functions can be sub-categorized into specific functions like [excuse], [persist], and [information] depending on the syntactic or pragmatic features and the state of the information which preceding and following phrases contain. (4) This phenomenon suggests the meaning of a certain grammatical expression is not fixed but keeps on changing in discourse. (Hankuk University of Foreign Studies)