Towards an analysis of discourse 25Very frequently, if the teacher accepts a reply without evaluating, the class
offers another reply without any prompting.
THE STRUCTURE AND CLASSES OF EXCHANGES
There are two major classes of exchange, Boundary and Teaching. The
function of boundary exchange is, as the name suggests, to signal the beginning
or end of what the teacher considers to be a stage in the lesson; teaching
exchanges are the individual steps by which the lesson progresses. Boundary
exchanges consist of two moves, framing and focusing; often the two occur
together, the framing move frequently occurs on its own, the focusing move
does so only rarely. A typical boundary exchange is:
The definition of teaching exchange given above is vague, but there are
eleven subcategories with specific functions and unique structures. Of the
eleven subcategories six are Free exchanges and five are Bound. The function
of bound exchanges is fixed because they either have no initiating move, or
have an initiating move without a head, which simply serves to reiterate the
head of the preceding free initiation.
Free exchanges
The six free exchanges are divided into four groups according to function,
and two of the groups are further subdivided according to whether teacher
or pupil initiates, because there are different structural possibilities. The
four main functions of exchanges are informing, directing, eliciting, and
checking, and they are distinguished by the type of act which realizes
the head of the initiating move, informative, directive, elicitation and