Theory of phonetics

III. Functional aspect of word stress.
Word stress in a language performs three functions:
1). Word stress constitutes a word, organizes the syllables of a word into a language unit having a definite accentual structure, that is a pattern of relationship among the syllables; a word doesn’t exist without the word stress. Sound continuum becomes a phrase when it is divided into units organized by word stress into word. It fulfills the constitutive function.
2). Word stress enables a person to identify a succession of syllables as a definite accentual pattern of a word. Correct accentuation helps the listener to make the process of communication easier, whereas the distorted accentual pattern of words, misplaced word stresses prevent normal understanding. This function is known as identificatory (or recognitive).
3). Word stress alone is capable of differentiating the meaning of words or their forms, thus performing its distinctive function. The accentual patterns of words or the degrees of stress and their positions form oppositions. For example,
'import – to im'port (to differentiate the noun from the verb).
'billow – be'low.
We can’t help saying a few words about logical and emphatic stresses. The main idea of the logical stress is to single out a word or a word combination which is the most essential from the point of view of meaning. For example,
This 'blackboard is \green.
The idea of this sentence is to say that the colour is green not red, yellow or brown. This concept is based on the contrast because the word which is marked by stress is opposed to any group of words that can be contrasted to the word in question. Thus in the sentence we contrast the word “green’ to any other colour. It should also be noted that in the same sentence logical and syntagmatic stresses fall on one and the same word “green’. Thus the function of these stresses are widened and in this case when two stresses are merged in one they signal the end of the sentence, show the logical centre in the sentence and bring up the idea of contrast.
The major function of emphatic stress is to express emotional and evaluative overtones. For example,

• 
  Where were you born?
  
• 
  I was found.
  
• 
  Found ?! (Oscar Wilde)
  

It often happens that different types of sentence stress go together and sometimes are hard to distinguish from each other. In this example “Found ?!” is marked by both an emphatic stress and a logical one. Since our speech is more frequently attitudinal in the sense that we often speak not only for the sake of conveying information but also for the sake of conveying attitudes and emotions. It would be correct to speak of a logical-emphatic stress.