A study of functional-semantic fields theory and application of the same comparative and contrastive researches

This article is about the functional-semantic fields theory and application of the same comparative and contrastive researches by using the functional grammar of language. This approach is based on idea and concepts of Russian linguists including some practical instances of their researches. The functional-semantic fields, based on definition, are the grammatical and lexical units or combination of them which based on a specified semantic category considered as a group and they have a relation by the common meaning application.The functional-semantic fields have different types. In this paper, in particular, functional-semantic field is investigated based on the semantic category of "possibility". The main goal of this study is to show how this theory can be applied to analyze a semantic category by the grammatical and lexical tools and the importance of this theory regarding to study of language internally and interactionally to find a suitable way to optomize or change of learning foreign language styles to language learners.