Brown and Yule (1983) suggest that language has two main functions : interactional and transactional. The interactional function is concerned with the maintenance of social relationships - for example, if two people pass in the street and say ...
A : Hi, all right?
B: Yeah, fine thanks.
... the function of the exchange is purely interactional - it serves only as an acknowledgement of the relationship, and the answer is conventional - it may not even actually be true.
Transactional discourse, on the other hand, is concerned with the transmission of information. If at the greengrocer's I say ..
A: Two pounds of cherry tomatoes.
... it is important that I transmit, and the greengrocer understands, the information accurately : so that for instance I don't end up with three kilos of plum tomatoes. If the greengrocer has any doubts he might ask for further information
A: Two pounds of cherry tomatoes.
B : These ones, or the ones next to the potatoes?
A: The ones next to the potatoes
B : That's £5
The "purely interactional" example given above is an example of phatic communion. Most language is, of course, not "purely" transactional or interactional but a mix of both, and for this reason Brown and Yule (ibid) suggest that exchanges are generally better described as primarily transactional or interactional. Social chat will contain some information - eg if I'm telling you about my last holiday - but it remains primarily interactional in terms of its function. It doesn't really matter if you don't retain the details. And transactional exchanges will often be interspersed with elements which are there to serve an interactional function. Compare the exchange above with :
A : Good morning. Can I have two pounds of cherry tomatoes.
B : Would you like these ones, or the ones next to the potatoes?
A: The ones next to the potatoes please.
B: Here you are. That's £5 please.
A: Thank you.
None of the underlined elements are essential for the transmission of information, even though the exchange remains primarily transactional. They serve an interactional function.
Both primarily interactional and transactional language may involve either long or short turns. Eg:
Transactional long turn - a presentation or lecture.
Transactional short turns - the greengrocer's conversation above.
Interactional long turns - recounting an anecdote
Interactional short turns - social chat.
Reference
Brown, G. and Yule, G., 1983, Teaching the Spoken Language, Cambridge : CUP
