1. the subject of theoretical grammar its relations to other branches of linguistics

52. . ESSENTIAL FEATURES OF THE SENTANCE
A sentence is a unit of speech whose grammatical structure conforms to the laws of the language and which serves as the chief means of conveying a thought. A sentence is not only a means of communicating something about reality but a means of showing the speaker’s attitude to it.
It is rather difficult to define the sentence as it is connected with many lingual and extra lingual aspects – logical, psychological and philosophical. We will just stick to one of them - according to academician G.Pocheptsov, the sentence is the central syntactic construction used as the minimal communicative unit that has its primary predication, actualises a definite structural scheme and possesses definite intonation characteristics.
The most essential features of the sentence as a linguistic unit are a) its structural characteristics – subject-predicate relations (primary predication), and b) its semanticcharacteristics – it refers to some fact in the objective reality.
According to the purpose of the utterance we distinguish 4 kinds of sentences:
1- The declarative sentence states a fact in the affirmative or negative form. In DS the subject precedes the predicate (pronounced with falling intonation) (!: English predicate can have only one negation).
He does not go anywhere.
2- An Imperative sentence serves to induce a person to do smth, so it expresses a command (falling tone: Come to the blackboard!), a request or invitation (rising tone: Open the door, please!). 
3- The interrogative sentence asks a question. It is formed by means of inversion (unless subject is an interrogative word: Who is in the room? – no inversion). 
There are several kinds of questions:
General questions requiring the answer yes or no and spoken with a rising intonation. They are formed by placing part of the predicative (auxiliary or modal verb) before the subject. 
Do you like art? Can you speak English?
Astonishment: Haven’t you seen him yet?
Rhetoric questions: Can you commit a whole country to their own prisons? 
Special q. beginning with an interrogative word (falling intonation) 
Where do you live? (order of words is as in Gen. question)
Who lives in this room? (Who – is a subject, order of words is as that of a statement)
Alternative questions, indicating choice 
Do you live in town or in the country? 
Disjunctive questions requiring the answer yes or no and consisting of an affirmative statement followed by a negative question, or a negative statement followed by an affirmative question 
You speak English, don’t you? 
4- An exclamatory sentence expresses some kind of emotion or feeling. It often begins with the words what and how, it is always in the declarative form (no inversion) (falling intonation: What a lovely day it is! How wonderful!)