Having a clear view of the nature of language is always considered as a matter of great practical value in teaching and learning a foreign language ( for more details see R.C. Lugton , P. 25). This is due to the fact that language, as it is commonly defined , is a system starting from the smallest significant unit namely the phoneme up through the largest structural unit namely the sentence. As far as language is a system of communication, it is implicitly understood in passing successful classroom exercises, the communicative nature of language should be heeded to a large extent. Therefore, it is desirable to retain contact whith the vocal sounds of language in order to meet the students needs (Langacker : language and Its structure.). Since it is believed that the cognitive theory is most suitable for teaching English as a foreign language, consequently, this paper represents a try to treat the congnitive theory and its both reliability and application at the university level. Before examining the application of the cognitive theory to classroom environment, it is of practical Utility to go through its basic Prisciples in order to throw light on its linguistic aspects and to discover to what this theory could be applied. Thus, the first part of this Paper will be defined