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Grammatical forms of discourse markers

Different grammatical forms can fulfil the same marking function. For example,

the following forms can all be used to prepare the listener for a new topic or for a

shift in the current focus of the topic:

Incidentally, Rita’s going to come round tonight. 

(adverb)

By the way, Rita’s going to come round tonight. 

(prepositional phrase)

While I think of it, Rita’s going to come round tonight. 

(finite clause)

Speaking of which, Rita’s going to come round tonight. 

(non-finite clause)

Listen, Rita’s going to come round tonight. 

(imperative clause)

Hey, Rita’s going to come round tonight. 

(interjection)