This rapport comes under the heading of Prague School. It aims to shed light on phonology in the eyes of Prague  school,  and the contrast of elements to one another.
We give a definition to this school and try to explain the concept of “ phonological contribution “ by giving more details , and more examples.  Last but not least , we focus on Distinctive features to put the learners on the image. Finally , we resume our information in a small conclusion .
I.	Definition:
a.	PRAGUE SCHOOL.
In 1920 , VILEM Mathesius established the prague school, which is a school of linguistics thoughts and analysis . It also become well known by its scholars Nickolai tubertzkoy and Roman Jacobson . According to this school,  we should study linguistics respecting the relation between all the elements. Linguists focused on phonemes.
b.	PHONOLOGICAL CONTRIBUTION.
In this study Nikolai T and his followers defined phonemes as sets of distinctive features. In other words he did not consider the phoneme to be the minimal unit of analysis. For more illustration we have some examples:
/p/ , /b/ ; /t/,/d/;/k/ /g/ they differ in terms of their articulation I.e it may be said that there is just one feature which is voicing. ( vibration of vocal cords).
Similarly,  the labiality features can be contacted from /p/,/b/ by comparing them with /t/ /g/.
The feature of nasality from :/n/, /m/ comparjnv them with /t/ ,/d/

To sum u, linguists of prague seeathat each phoneme is composed of a number of articulatory features and is distinguished by the pressure on the absence of at least one feature from every other phoneme of a language.