The present paper focuses on grammatical rules being taught to the students of advanced English classes and contemplates the question of over-simplification of these rules in order to make the grammatical system of the English language more understandable and learnable. The classes in question are of B1 level, which means that the intermediate or advanced knowledge of the language is presupposed. The Common European Framework of Reference for Languages (CEFR) describes a B1 level user as an independent speaker, who is capable of understanding standard matters in a familiar setting such as school, work or leisure and who can describe and express his/her plans, ambitions, dreams or opinions in a more complex way. The question arises whether, on the ground of grammar, it is good or bad to adhere to the rules sufficient to such communication situations or whether to provide the students with a deeper insight into the problem. To support her point of view, the author analysed 25 students' works which comment on the most frequent grammatical errors in a written form. The analysis focuses on the description of the most common deviations from the correct use of the English temporal system.
