Learning a foreign language takes place out of touch with the natural communication environment and students perceive a foreign culture through their mother tongue. Trying to speak a foreign language students of non-linguistic faculties make a lot of mistakes in the grammatical structure of sentences that lead to misunderstanding. The article deals with the issue of students’ disability to express their ideas in a foreign language. The main problem of mastering a foreign language lies in the difficulty students meet when learning English grammar. Based on mother tongue principle, the authors suggest students should form a systematic perception of English grammar for further teaching them techniques of recoding their own ideas from their mother tongue into a foreign language. For this purpose they offer to use a method of teaching English under the conditions of mixed subordinate bilingualism: teaching students to identify interlingual similarities and differences by doing exercises in two-way translation. The research shows that using mother tongue principle diminishes students’ difficulties in learning English grammar and helps them to make correct sentences in a foreign language. Developing a communicative competence in students is impossible if they don’t understand the structure and the logics of a foreign language, can’t correlate it with their mother tongue and don’t understand interlingual similarities and differences. The results of the research prove the efficiency of the offered method. Deliberate use of various language means and ways of forming utterances based on mother tongue principle must be an obligatory component in teaching a foreign language in non-linguistic institutes.

Keywords: mother tongue principle, mixed subordinate bilingualism, difficulties in teaching English.