The sentence-final form mono / mon is frequently used in Japanese conversations. Recent studies (Takahashi,1994; Hashimoto 1998, 2000) have identified mono as a 'discourse modality' indicator. However, due to unauthentic and insufficient data sources, none have fully examined the diverse discourse structures and interactional functions of mono-usage in various contexts.
This paper discusses how mono contributes to the cohesion of on-going talks by organizing the sequences, and how it shows speakers' attitudes towards both propositions and addressees. Upon analyzing the structural patterns of mono-utterances in natural conversations, I divide mono into two types:
1) The "self-justification mono," which serves to justify the speaker's position that has been explicitly or implicitly challenged, as in (1):
(1) From a conversation between a husband (H) and a wife (W).
H: Sugoku kitanai ne.
It is very dirty, isn't it.
W: Datte isogashii n da mon.
But I am busy mono.
2) The "other-justification mono," which functions to support the position of others, primarily of the prior speaker, who tends to challenge a 'third party' outside the conversation, as in (2):
(2) W complains to T about the topic of her final paper.
W: Sore, chotto muri janai.
That is unreasonable, isn't it?
T: Soo. Datte, zenzen tsukawanai mon.
Right. Because (we) don't use it at all mono.
Borrowing Cook's (1992) model of indexicality, I further argue that the underlying causal logic marked by mono forms its direct indexical meaning, which extends to indirectly index multiple contextual bound meanings. By marking the logic as an "inevitable" and "natural" consequence, mono qualifies speakers' reasoning as generally accepted knowledge located within "common grounds." Hence, rather than neutrally providing supplementary information, mono conveys speakers' subjectivity such as "The reasoning is obvious, isn't it?!" or 'It's beyond my control'. The expressive functions are rooted in the causal logic.