One important property of a sentence is its communities act potential.
Sentences with different structures often have different communicative functions – they are conventionally used to perform different communicative acts in speaking.
Thus, a speaker who wants to assert or state that something is true will normally utter a declarative sentence such as Snow is white.
On the other hand, if the speaker wants to issue an order, request, or command, then an imperative sentence such as Leave the room! is appropriate.
Finally, if speaker wants to ask a question, then the obvious choice is an interrogative sentence such as What time is it? As a first approximation we could diagram these facts a s follows:
a. Declarative sentence – Used to constate (assert, state, claim, etc.)
b. Imperative sentence – Used to direct (order, request, command, etc.)
c. Interrogative sentence – Used to question.
It seems to be a part of the semantics of these structural types (declarative, imperative, interrogative) that they have the distinct communicative function as above.
In any event, we would not say someone understood sentences of these types unless that person understood the differences in communicative function.
That these different types of sentences had these different normal uses is an important semantic fact.
However, the field of semantics has traditionally concentrated on the assertive function of language, concerning itself mainly with the properties and relations that declarative sentences have regarding truth.
Communicative Act Potential
