Language in use is about how language is used by the speaker and perceived by the hearer. Talking about language in use is talking about Pragmatics. Pragmatics is one of the items in the trichotomy of the general science of signs (read: Semiotics). The trichotomy, by Charles Sanders Peirce, is syntactic-semantics-and pragmatics.
The syntax is about words connection; the connection of grammatical structure of the sentence, the form of a sentence. Syntax studies the connection among signs without considering the meaning of signs, the specific signification, and the function of relation among signs.
John ate donut
The sentence above is meaningful in a perfect grammatical structure. Syntactically, although the sentence is restructured become:
Donut ate john
The sentence is syntactically correct. The connections of signs are true. However, is it possible that donut can eat John?
Semantically, the second sentence is illogic. Semantics is about the meaning of the signs connection. John and ate is correctly connected, donut as the object is required because verb ate is a transitive verb. John function as the actor who performs ate and donut as the patient that is the verb ate performed on. The connections among entities in the sentences are logic.
When the sentence is restructured become Donut ate John, the connections become illogical. The meaning of Donut is food, and it is impossible that a kind of food eats human. Here, it can be seen that the difference between syntax and semantics is that if the syntax is about the structure without meaning, semantics studies the structure and the meaningfulness of signs connection. Therefore, syntactically the restructured sentence is meaningless or unacceptable.
Nevertheless, sometimes we may find that kind of sentence (Donut ate John). It may have meaning like: Donut is actually a name of the monster. The sentence may be used in certain context for certain purpose. Here, pragmatics plays its role.
Pragmatics concerns signs as well, but it is more about how those signs are used and interpreted. How do people produce, offer, and interpreted language? The sentence given may be used as a joke, insult, and so on.
Pragmatics is concerned with the study of meaning as communicated by a speaker (or writer) and interpreted by the hearer (or reader). Therefore, pragmatics is the study of the speaker meaning, in certain context. What meant with context is whom they are talking to, where, when, and under what. Pragmatics also studies how more gets communicated than is said. Pragmatically, we cannot understand the sentence “Donut ate John” literally, but we should look deeper, what the speaker’s meaning is. Pragmatics is also the study of the expression of relative distance, or the relationship of interactants.
People expressions are different each other, or people express their meaning for one differently to other. For the example, you can say “Open the door!” to your friend, your younger brother or sister, but you cannot say it to your lecturer that way. To do that expression, you may use more polite utterance “May the door is opened?” or “It is very hot here” or other way. What makes you do this is the difference of relative distance.
It is clear that pragmatics is about how people use language in the certain context for certain purpose. In pragmatics, we will find some tools to be used to analyze the speaker meaning or the meaning of an utterance in context.