The interpersonal function [of language] is the function “to establish, maintain, and specify relations between members of societies” - Michael Halliday

I see it as part of the development of the field. I would always emphasize how much I share with other linguists: I've never either felt particularly distinct or wanted to be distinct. I never saw myself as a theorist; I only became interested in theory, in the first place, because, in the theoretical approaches that I had access to, I didn't find certain areas developed enough to enable me to explore the questions that I was interested in.

The theme is what is being talked about, the point of departure for the clause as message, and the speaker has within certain limits the option of selecting any element in the clause as thematic.

Language... is a range of possibilities, and an open end set of options in behavior that are available to the individual in his existence as social man. The context of culture is the environment of any particular selection that is made within them... The context of culture defines the potential, the range of possibilities that are open. The actual choice among these possibilities takes place within a given context of situation.