Back channel is defined as "signal of attention and interest" (Yngve, 1970), "listner's signal of participation" (Duncan and Fisk, 1977) or "continuer" (Schegloff, 1982). The problem is (a) the definition of back channel varies among researches, and (b) the expanded notion of back channel creates ambiguity and confusion in deciding if some varieties of back channel signals are to be counted as speaking-turn utterances.
In this study, a new model of analysis was proposed by incorporating two parameters. One is the concept of floor. It was argured that utterances can be classified into two types of turns, back channel and main channel. The basic function of back channel is to support the floor, which exists at the highest level of discourse structure, and that of main channel is to yield and maintain the floor. Another parameter is the intention examined from the perspective of the speech act theory (Austin, 1962). Back channel utterances must be cooperative and positive, and if we follow Fraser (1974)'s classification, they perform illocutionary acts such as assertion, reflection, request, and suggestion.
Naturally recorded English conversation was analyzed through these parameters to demonstrate that this model can a) distinguish back channel utterances from main channel utteraces more clearly and b) identify the inherent nature of the function more correctly.