Grammar in natural interaction is an emergent, dynamic and adaptive system that is consistently subject to change. It is understood as a collection of open multiple subsystems, each of which is activated as the language users recurrently participate in a particular linguistic, interactional and social activity. When a certain linguistic form or combination of forms are utilized across highly distinct linguistic environments, e.g. spontaneous conversation vs. highly-planned writing, responding to the different environmental requirements and also to the types of recurrent activities that particular form is closely involved, highly rich and diverse functions and significances emerge, which gradually develop into an overall component grammar of that particular linguistic environment. Based on the above conceptual model of grammar and interaction, this dissertation explores the use of Japanese clause-ending form TE in ordinary conversation and highly-planned written text. From a discourse-functional perspective, it is demonstrated that in the written environment, the form TE, as opposed to its counterpart form of conjunction, tends to function as a marker of semantic subordination and also as a marker of local discourse continuity: i.e. what has already been commonly discussed as the major functions of TE. However, in a clear contrast, TE in ordinary conversation is exploited by the participants in quite distinct ways, beyond the conventional understanding of how this "grammatical," "bound" and "semantically vacuous" particles should behave. A CA-inspired interactional linguistic approach to the form's conversational significances further reveals that the form's inherent "non-finiteness" and "continuity" marking can significantly serve for the interactants' display of mutual orientation, for their understanding and negotiation of the emerging talk shapes, as well for their systematic sequencing of various actions that are collaboratively built upon the unfolding units of talk. These imports of the form TE are further enhanced in accordance with the workings of other relevant concurrent resources, including syntactic, prosodic and bodily. It is further suggested that largely due to the environment's contingent nature, the correlation of a language form and its significances in ordinary conversation tends to be relatively loosely and flexibly realized, compared to the tighter "meaning/form"--"function" associations in a planned written environment. However, I believe, it is still possible to track the most fundamental characteristics of the linguistic form as its common working(s) across these distinct linguistic environments, and its careful descriptions can suggest an integrative conceptualization of grammar as an overarching system across different linguistic, interactional and social activities. The current study serves as an empirical case study in pursuit of grammar at its interfaces with interaction and social action. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]