There are more than 300 different definitions of the sentence, but not a universal one

The sentence.
There are more than 300 different definitions of the sentence, but not a universal one.
5 approaches to the definition of the sentence:
Logical, psychological, phonetic, graphical, grammatical.
Logical: “a sentence is an expression of a complete thought, it’s a judgment or a proposition”.
Blokh: “the sentence is a unit of speech, built up of words according to a definite syntactic pattern and distinguished by a contextually relevant communicative purpose.”
Foreign scholars against this definition, as the meaning isn’t an integral part of a sentence.
Psychological Шахматов: a sent.is a psychological phenomenon which is expressed grammatically.
Phonetic approach: Paul Roberts :a sent. is a succession of sounds divided into brief groups by pauses required for taking breath”.
Cons of this approach: 1) the sent. can be considered only in oral communication; 2)the impossibility to single out a composite sentence because there is a pause in the inner structure of a composite sentence as well.
Graphical approach: sent. – a succession of words between 2 full-stops”.
Cons of this approach: the sentence may be defined only in writing.
Grammatical. In modern grammar: “ a sent. – is a grammatical unit”.
C.Freeze: “ a sent. – a minimal free-utterance”.
L.Bloomfield: “a sent. – a free linguistic form,which isn’t a part of any other linguistic form”.
Problem is: should a sentence be regarded as a unit of language or speech?


27. The Simple Sentence.
the simple sentence is a sentence in which only one predicative line is expressed.
Thus, we may state, that a proper simple sentence, or a single-clause sentence, to put it more exactly, is a monopredicative unit, as distinguished from composite and semi-composite sentences.
Predication makes the sentence the sentence. Predication – is a special category, which establishes the relations of the named phenomena to actual life.
Predicative relations – are those between the subject and the predicate, when the predicate says smth about the subject and the subject determines the form of the predicate.
Modality (peculiar to sentences only) – shows the attitude of the speaker to reality.
Types:

• 
  Objective – reflects the con-n between the name and obj. reality, it represents the action as real (unreal, possible, necessary)
  
• 
  Subjective – shows the personal attitude of the speaker to the situation.
  

Means to express modality (Biber):

• 
  Moduses
  
• 
  Stence markers – express personal feelings, attitude, personal judgement (modal words, mod. Verbs, adverbials)
  

Stence divices – paralinguistic means (body position, gestures)
In the sentence we speak about syntactic modality ( relation between the subject and the predicate) the basis of predicative relations


The sentence – nominal function + express predication ( deals with modality)