CASE SYSTEM OF THE RUSSIAN LANGUAGE: DIFFICULTIES OF MASTERING AND EXPERIENCE OF OVERCOMING THEM

The case system of the Russian language is very difficult for foreign students because all cases are polysemantic, the amount of values is not the same; in addition to the main system endings, there are a large number of exceptions; there is an internal interference associated with homonymous endings of different cases and with homographs. The choice of a particular way of presenting grammatical material, or approach, is due to some reasons, the main of which are:


INTRODUCTION
The case system of the Russian language is the most difficult part of grammar for foreign students. The reason for this, of course, is either the lack of nominal inflection in the native language of the foreign language, or the discrepancy of this system in the studied and native language (Unezheva, 2016, p. 201). Difficulties are caused by "the polysemy of cases, the variety of inflections, the changing of forms and alternation of the bases of singular and plural nouns, pronouns, adjectives, numerals, ... prepositional case management" (Valizadeh, 2017). In addition, "problems in the development of the case system of the Russian language by foreigners are caused by interference" (Kholodkova, 2012, p. 275).
Thus, the Russian case system is more difficult for foreign students, as: a) All cases are polysemantic, the number of values are not the same (for example, about 10 values of the genitive, about five values of the dative and prepositional cases); b) In each case, in addition to the main system endings, there are a large number of exceptions (for example, in the prepositional case, the main ending is -e, the second system ending is -и, and the nonsystem ending is -у/-ю); c) The form changing can take place by alternating basics (рот -рта, сѐстры -сестѐр); d) The internal interference associated with homonymous endings of different cases: музыку (accusative singular feminine) -другу (dative singular masculine); and homographs: окна (nominative case plural neuter) -окна (genitive singular neuter).
However, full communication in Russian without knowledge of the case system is impossible, therefore, in the methodology of teaching Russian as a foreign language is constantly working to improve approaches, techniques and pedagogical technologies, including multimedia (Morozovska, 2016), which are used in the study of this grammatical material.
It is proposed, for example, "a comprehensive linguistic analysis of the category of case, the application of which in the classroom on Russian as a foreign language... will contribute to the effectiveness of training and revision of approaches to teaching the case system" (Morozovska, 2016, p. 197). Within the communicative trend in teaching Russian as a foreign language proposed situational motivation, that is, demonstration to foreign students that incorrect use of cases results not only in violation of the rules, but also in communicative failure. It is also said about the "principle of continuity and perspective" in teaching foreign students the case system of the Russian language (Zlobina, 2011, p. 43).
In textbooks and manuals grammatical material on this topic is also served quite differently both in terms of the order of the study of cases, and in terms of the method of presentation of the material. The study of the case system in some manuals begins with the accusative case, in otherswith the prepositional, in the third with the genitive. Compilers of some manuals adhere to the "horizontal" presentation of the material, in which each new case is studied thoroughly with all endings, meanings for all nominal parts of speech. In other manuals the concentric approach assuming gradual expansion and complication of a material is used: at first the most important values of all cases at the use of nouns in singular and personal pronouns, thenat the use of nouns in plural, finishing with studying adjectives and pronouns.
Thus, the purpose of our article is to summarize the experience of teaching the case system of the Russian language and to develop a systematic approach to the study of this grammatical topic.
To achieve this goal, we have solved a number of tasks: 1) Describe the existing points of view on teaching foreign languages prepositional-case system of the Russian language; 2) Justify the developed in the process of teaching this grammatical topic own approach to the study of Russian cases; 3) Determine the sequence of the introduction of cases; 4) Determine the range of important communicative values necessary for the study at the initial stage.

CASE SYSTEM OF THE RUSSIAN LANGUAGE: DIFFICULTIES OF MASTERING AND EXPERIENCE OF OVERCOMING THEM
In practice of teaching Russian as a foreign language we use 2 approaches to studying the prepositional-Proceedings of INTCESS 2020-7th International Conference on Education andSocial Sciences 20-22 January, 2020 -DUBAI (UAE) case system of the Russian language: 1) Concentric, in which all cases of nouns are first studied, but in each case only one, two meanings maximum and only in the singular form are actualized. For example, the genitive case is the meaning of absence. And then students get acquainted with each case again, but in detail, studying all forms of singular and plural nouns and adjectives and all the meanings in which this case is used; 2) Linear ("horizontal"), in which one case is first studied "entirely". And then we pass to another case, which is also thoroughly studied. And the same goes for all six cases.
The choice of the approach is dictated by several factors: 1) The time of arrival of the students. If time is short, the pace of learning will be fast. With intensive study of the case system, it is better to use a linear approach, since the concentric approach requires more time to repeat the endings of one case without introducing a new material, since the next new material will be another case. With the linear approach, it is possible to introduce new material at every lesson, while repeating the endings of the forms of nouns and adjectives of the same case occurs in parallel with this introduction: when memorizing verbs, after which the given case is used, when studying all the meanings in which the given case is used. Nouns and adjectives in the studied constructions have the form of one case, change according to the same model, and case endings are absorbed better. If the group has enough time, the concentric approach allows to achieve great results, since the main meanings of cases are well practiced and remembered, in the minds of foreigners there is a clear distinction between the singular and plural, forms of nouns and adjectives. In the transition from study to a more detailed study, students already have some idea of the General outline of the case system.
2) The intellectual level of the group. Weaker groups require a constant return to the already passed, repetition with an explanation at a more advanced level of the previously studied material. The concentric approach meets these requirements and is therefore more productive in such groups. Even with partial assimilation of the material, students will have an idea of the entire case system.
It is necessary to pay attention to the fact that at different approaches different order of studying of cases is shown. With the concentric approach after the nominative, it is logical to study the genitive case in the meaning of absence. The construction "У меня есть "I have" + noun in the nominative case" requires a logical continuationthe construction "У меня нет "I don"t have" + noun in the genitive case" (genitive in the meaning of absence -нет кого? нет чего?). And then in the following order: accusative case (in the meaning of a direct object -что? кого?) → prepositional (in the meaning of the place -где?) → dative (in the meaning of the addressee -кому?) → instrumental (in the sense of compatibility -с кем?).
With repeated, already complete and detailed study of cases, as well as with a linear approach, the order is already different: nominative → prepositional → genitive → accusative → dative → instrumental. This order is due to several reasons, which will be discussed below.
At the same time, in our opinion, special attention should be paid to case terminology, namely, the names of cases. Undoubtedly, the names of cases are difficult words for a foreigner, but, in our opinion, it is advisable to use these terms. First, these terms are clear to all native speakers of the Russian language. If foreign students will help in the development of the case system of their Russian friends, there will be no terminological misunderstanding. Secondly, and, in our opinion, the most important thing is that such terminology can be used in any method of studying cases. In some manuals there is a use as names of cases of their serial number: nominative -1, genitive -2, dative -3, accusative -4, instrumental -5, prepositional -6. This nomination, justified from the point of view of a native Russian speaker, is not always clear to a foreigner. He has no idea about the "correct order" of cases. Moreover, as noted above, the teacher introduces foreign students to cases in a different sequence. Therefore, it is difficult for a foreigner to explain why the case 1 is studied first, and then, the case 6. If you number the cases as you study, then in different techniques, the same case may have a different number.
We would like to emphasize once again the difference between studying cases in the Russian school from acquaintance with the case system in the Russian as a foreign language. Another important point is the case questions. The methodological error of some teachers is the presentation of the usual case questions: nominative -кто? что?, genitive -кого? чего?, dative -кому? чему?, accusative -кого? что?, instrumental -кем? чем?, prepositional -о ком? о чѐм? In the study of cases it is necessary to go from the values in which cases are used, and it is these values that will dictate the questions. For example, in the prepositional case we distinguish 5 main values: place (где? -на столе "on the table"), the object of speech (о ком? о чѐм? -о маме, об экзамене "about mother, about examination"), time (когда? -в апреле "in april"), transport (на чѐм? -на автобусе "by bus"), clothes (в чем? -в рубашке, в джинсах "in shirt, in djeans"). As can be seen from the above examples of questions much more than studied in the Russian school, because for a Russian person it is clear that the questions о чѐм? на чѐм? в чѐм?these are different forms of the same question, and for a foreigner these are different questions. In addition, if the choice of a particular case in the mind of a foreigner will be associated with the situation, so the value that is required in a given situation of speech, then foreign students will be able (with the necessary grammatical forms) to build speech and not just to answer questions. Often there is a situation when while answering questions, students do not have difficulties in choosing the form of a noun or adjective, because they have learned the correspondence of the questionthe case form. But in the flow of speech, when there are no questions, the foreigner cannot change the words correctly.
Let us consider in more detail the method of studying each case.

Prepositional
The study of the prepositional case first (after the nominative) justified by several reasons: 1. High communicative importance of the question where? Foreign students learn the ways of expressing spatial meanings at the very beginning of learning the Russian language (adverbs that answer the question where: here-there, right-left, far-near, etc.). The ability to determine the location, to inform about location ensures survival in the new language environment.
2. Apparent simplicitythe same endings for all nouns (masculine, feminine, neuter). Therefore, in both linear and concentric approaches, the first meaning of the prepositional case is the place of action (в университете "at the university", на уроке "on the lesson".
Often, especially in the practice of novice teachers, at the initial presentation of cases to foreign students, the so-called case questions are first presented; in this case, questions о ком "about whom"? о чѐм "about what"? Russian grammar is not yet understood by beginners. This creates great difficulties in learning, because beginners do not yet have an idea about the system of the Russian language, its grammar.
At the initial stage of acquaintance with cases it is necessary to enter only those values which are actual for foreigners, i.e. have high communicative significance. The study of the prepositional case begins with the meaning of the place: the difference is demonstrated in the use of prepositions в and на (в университете на уроке "at the university in the lesson", в лаборатории на занятии "in the lab on the lesson"), and rules for the use of the endings -e and -и. Non-system ending -у is introduced to words used in the initial stage of training (на полу, в шкафу, в лесу 'on the floor, in the closet, in the woods", etc.). The difficulty for foreigners may be the fact that the use of prepositions в (in) and на (on) does not always correspond to certain meanings. It is known that the preposition в (in) has the meaning "inside", and the preposition на (on) has the meaning "on the surface": в общежитии "in the hostel" -на улице "on the street". You can demonstrate this difference by showing, for example, a book: on the table or in the table. However, there are cases of the use of the preposition на (on), which you need to remember: на Родине "in the homeland", на заводе "at the factory", на вокзале "at the station", etc. It should be noted that the work with the prepositions в (in) and на (on) will be continued in the study of genitive and accusative cases and verbs of motion.
The meaning of the object of thought and speech (о ком? "about whom?" о чѐм? "about what?" -о маме, о Москве, об экзамене "about mother, about Moscow, about examination" is entered after studying and fixing of local value. It is necessary to pay attention to the use of forms of the preposition о (about) -об, обо.
the prepositional case also has the meaning of time. The question когда? "when?" by the time of studying the prepositional case is already familiar to foreign students. When studying this meaning, it should be noted that the prepositional case for expressing time segments is used when indicating the month -в январе, в феврале "in January, in February", etc., and the year -в тысяча девятьсот восемьдесят седьмом году "in nineteen eighty-seven". It is important to pay attention to the use of forms such as в этом году (месяце), в прошлом году (месяце), в следующем году (месяце) "this year (month), last year (month), next year (month)" -на этой неделе, на прошлой неделе, на следующей неделе "this week, last week, next week" focusing on the use of prepositions в (in) and на (on).
Although the verbs of motion have not yet been studied at this stage, but it seems appropriate to introduce into active use constructions that answer the question на чѐм? (on what?) with the meaning of means of transportation: на автобусе, на машине. на самолѐте "by bus, by car, by plane". Preliminary acquaintance with the basic verbs of motion идти-ходить, ехать-ездить is justified and meets the principle of advanced training.
To study another meaning of the prepositional case at the initial stage, we can suggest the construction быть, ходить в чѐм? to be in what? (Вчера она была в красном платье и в новой куртке; Она ходит в длинных юбках 'Yesterday she wore a red dress and a new jacket; she wears long skirts") This meaning is not considered in all textbooks intended for the initial stage of training, but the frequency and importance of this construction allows you to get acquainted with it when you first refer to the prepositional case. Subsequently, it can be correlated with the accusative case: носить что? (Она носит длинные юбки 'She wears long skirts")

Genitive
If about prepositional case almost all Methodists agree that it is necessary to study it first, i.e. immediately after the nominative, then about what case to study after the prepositional, there are different opinions. In our opinion, the concentric approach justifies both familiarity with the accusative case in the meaning of a direct object, but only with inanimate nouns (Я читаю журнал и слушаю музыку "I read a magazine and listen to music"), and the introduction of the genitive case in negation (У меня нет учебника и ручки "I do not have a textbook and pen"). With a linear approach, in terms of ease of subsequent acquisition of grammatical forms, we believe that it is more effective to study the meanings and forms of the genitive case, because the accusative case, which is studied after the genitive, will not present great difficulties when using both inanimate and animate nouns.
Familiarity with the meanings of the genitive case begins with the constructions нет…, не было…, не будет… "no..., was not..., will not...." This is supported by the fact that the structure у меня есть… "I have..." is already familiar to students. The need to give a negative answer makes the meaning of negation one of the main. Exercises for practicing positive and negative answers demonstrate the similarity of the forms of the neuter and masculine: у меня есть книга -у меня нет книги "I have a book -I have no book", у меня есть письмо -у меня нет письма "I have a letter -I have no letter", у меня есть карандаш -у меня нет карандаша "I have a pencil -I don"t have a pencil", as well as develop skills in the use of the past tense verb forms neuter: не было текста, не было задания, не было лекции 'there was no text, no task, no lecture".
The meaning of belonging (or subject of possession) is represented by the structures у брата есть машина "the brother has a machine" and это машина брата "it is the brother"s machine". Practicing these constructions, it is necessary to teach foreign students to ask questions and give correct answers: У кого есть машина? У брата. "Who has a car? The brother has". Чья это машина? Брата. "Whose car is this? Brother"s".
The spatial meaning expressed by the prepositions из and с (of) to denote the starting point of the movement (откуда? "where from?") is also very used: Я приехал из Египта. Я пришѐл с урока "I come from Egypt. I came out of the lesson". At the same time, the rule of using prepositions из and с is easily assimilated: the preposition из is the antonym of the preposition в, and the preposition с is the antonym of the preposition на. Prepositions в and на, the use of which was practiced in the study of the prepositional case, are repeated and used in various situations of speech communication: Я был в Москве "I was in Moscow" (где? "where?") -Я приехал из Москвы "I came from Moscow" (откуда? "where from?"); Я был на собрании "I was at a meeting" (где? "where?") -Я пришѐл с собрания "I came out of a meeting" (откуда? "where from?"). Answers to the question where from? are considered and in situations, when the starting point movement is animate face, in such answers is used the preposition от, for example, Я пришѐл от брата "I came from my brother". Thus it is necessary to pay attention of pupils that if at the answer to a question where? if an animate object is used, then the preposition y must be used in the answer; it should be noted that this is a form of the genitive case, not the prepositional one. To show the coordination of grammatical forms and to work out the use of prepositions in such constructions it is advisable to use the following examples: Я был в больнице у врача "I was in the hospital at the doctor"s" -Я пришѐл из больницы от врача "I came from the hospital from the doctor".
The meaning of quantity in the genitive case is worked out on the example of such quantitative-nominal phrases as a кусок хлеба "piece of bread", бутылка молока "a bottle of milk", стакан сока "a glass of juice" etc. But the greatest difficulty is the use of nouns with quantitative numerals and the words много, мало, сколько, несколько "many, few, how many, several" etc. It is important to carefully work out the use of the singular (after the numerals two, three, four) and plural (after the other numerals, starting with five) genitive: 20-22 January, 2020 -DUBAI (UAE) два друга -пять друзей -много друзей "two friends-five friends-many friends", три сестры -пять сестѐр -несколько сестѐр "three sisters-five sisters-several sisters", четыре письма -шесть писеммало писем "four letters-six letters-few letters".

Proceedings of INTCESS 2020-7th International Conference on Education and Social Sciences
The genitive case in the designation of the date is a weak point for many foreigners. Answering the question when? using the exact date (day, month), it is necessary to use the genitive form: Он родился пятого августа "He was born on the fifth of August". It is advisable to present similar constructions in comparison with other forms: Это случилось девятого мая "It happened on the ninth of may" (когда? "when?") -Сегодня девятое мая "Today the ninth of may" (какое сегодня число? "what"s the date today?"). If there is an indication of the year, it is also desirable to demonstrate the specificity of use: Сегодня десятое декабря две тысячи пятого года "Today the tenth of December two thousand and five". -Это произошло десятого декабря две тысячи пятого года 'It was the tenth of December, two thousand and five". In both constructions, the indication of the year is the samethe form of the genitive case (since there are other elements of the date). However, only the indication of the year requires a prepositional case, which has been studied previously: Это было в две тысячи пятом году "It was in the two thousand and fifth year".
The study of the genitive case is also necessary for the correct use of the form of the comparative degree of adjectives. In our opinion, students need to demonstrate different forms of use of the comparative degree with the genitive case and without it: брат старше сестры -брат старше, чем сестра "brother older than sister"; книга интереснее фильма -книга интереснее, чем фильм "the book is more interesting than the film". Close attention should be paid to special forms of formation degree of comparison: хороший -лучше "good-better", плохой -хуже "bad-worse", маленький -меньше "small-less", etc.
As already noted, the spatial meaning is one of the main ones for the genitive case, so it is important to study the prepositions of the genitive case with a spatial meaning: около дома, напротив остановки, вокруг стадиона, недалеко от парка, у окна "near the house, opposite the bus stop, around the stadium, near the park, at the window" etc. A special communicative significance has a construction with a preposition до: Как дойти (доехать) до…? "How to reach (get) to…?": Как дойти до банка? Как доехать до аэропорта? Как добраться до вокзала? "How to get to the Bank? How to get to the airport? How to get to the station?" Need pay attention and on polysemy some prepositions, for example the pretext у: у брата есть машинавчера я был у брата -преподаватель стоит у окна "my brother has a car -I was at my brother"s yesterdaythe teacher stands at the window".
When studying the genitive case, attention is also drawn to the type constructions: я узнал новости от друга, студенты старших курсов "I learned news from a friend, senior students" etc.
As you can see, the genitive case is the most polysemantic. The variety of meanings makes it difficult to study. At the initial stage, only those values that have high communicative significance are studied. However, a systematic approach helps to learn the forms and meanings of the genitive case.

Accusative
In both the concentric and linear approaches, the study of the accusative case begins with the use of the direct object (что? кого?). This accusative function is necessary for the study of the verb and its forms. Otherwise, the development of grammatical material will turn into a mechanical action that has no communicative value. The use of the accusative case to convey the meaning of a direct object allows the verbs studied to be included in sentences (Ахмед пишет (что?) письмо 'Ahmed is writing the letter", а Эмма слушает (что?) музыку 'Emma is listening to music". Я -хороший студент. Я всегда делаю домашнее задание "I'm a good student. I always do my homework"), compose elementary dialogues (Что ты ищешь? -Я ищу ключи 'What are you looking for? -I'm looking for the keys". Почему ты думаешь, что Антон честный? -Потому что он всегда говорит правду 'Why do you think Anton is honest? -Because he always tells the truth"), etc. Then foreigners are introduced to sentences in which the direct object is animate noun (Я люблю (кого?) сестру "I love my sister", Михаил ждѐт (кого?) преподавателя 'Michael is waiting for the teacher"). In our opinion, the study of the accusative case should be preceded by familiarity with the genitive case in any approach. With such a sequence, it is not difficult to assimilate the differences in the forms of animate (in the masculine gender coincide with the genitive case) and inanimate (in the masculine and neuter genders coincide with the nominative case) nouns. The forms of feminine nouns require separate remarks. Students learn well the difference between words with endings -а/-я -у/-ю in the accusative case) and words that end with -ь (the accusative form coincides with the nominative case). At the same time it is necessary to pay attention to the fact that the inflection-у/-ю is also used in the prepositional case шкаф -(где?) в шкафу, берег -(где?) на берегуexceptions that need to be remembered) and in the dative case (друг -(кому?) другу, окно -(куда?) к окну, преподаватель -(кому?) преподавателюforms of masculine and neuter words). Therefore, it is advisable to make exercises to compare and consolidate these endings.
In the concentric approach, primary familiarity with the accusative case is limited to the meaning of the direct object. In more detail, the forms of nouns in the plural, as well as the forms of adjectives and pronouns are studied either by repeated reference to the accusative case (concentric approach), or only after fixing the functioning in the above-considered meaning of nouns in the singular (linear approach).
Simultaneously with the study of the accusative case, foreigners get acquainted with the verbs of motion, since the use of this case as a designation of the direction of movement (куда?) frequency. To show the difference of forms in the designation of a place, it is necessary to compare different cases with different prepositions: куда? -в/ на + accusative case (there is displacement, are used the verbs of motion, the ultimate pointfinish) -Иван едет в офис на работу 'Ivan is going to the office to work". где? -в/ на + prepositional case (one place, no movement, no movement) -Иван в офисе на работе "Ivan is in the office at work". откуда? -из/ с + genitive case (there is displacement, can be used the verbs of motion, initial pointstart) -Иван едет из офиса с работы "Ivan is going from office with work".
Comparison of the questions куда? and где? and the correct use of them will help avoid mistakes when choosing the case of the designation of the place. Foreigners often confuse these two questions and, therefore, the choice of prepositional or accusative case causes difficulties. The similarity of prepositions and the existence of parallel constructions in the language: Вчера я был (где?) в больнице "Yesterday I was in the hospital" (prepositional case) and Вчера я ходил (куда?) в больницу "Yesterday I went into the hospital" (accusative case)determine the need for a more detailed explanation of this topic and consolidating it on a large number of examples.
When fixing the use of prepositional forms (где?), accusative (куда?) and genitive (где? and откуда?) for cases, exercises that include a regional component are effective, for example, " working with a city map, the use of which will facilitate the adaptation and orientation of students. At the same time, speech models can be worked out, helping in everyday communication situations to find the way to the right place in the city, to learn information about the location of an object, which provides access to the communicative level, communication with such a type of speech activity as speaking" (Kozhemyakova, 2017, p. 179).
Special attention should be paid to the constructions with the verbs класть -положить, ставитьпоставить, вешать -повесить, which also require the accusative case. In the practice of teaching Russian as a foreign language we pay attention to the comparison of sentences such as:
Constructions of the first type are built on the model: subject (кто?) + verb класть -положить, ставить -поставить, вешать -повесить + place (куда?), and the second-by type: subject (что?) + verb лежать, стоять, висеть + place (где?). As in sentences with verbs of movement, the accusative case is used to denote the movement of an object, it should be emphasized that the grammatical subjects in the constructions of the first type are animate nouns, while in sentences of the second typeinanimate, it is the object itself that has been moved.
The accusative case is also used to denote time. In this sense (the answer to the question когда?) are used in different cases. It is necessary to pay attention to the fact that the accusative case is applied only when we talk about the day of the week (Мы ходили в музей в пятницу 'We went to the Museum on Friday") or the time on the clock (Магазин открывается в час 'The supermarket is opened at one o'clock"). In these constructions, as in sentences with the prepositional case, the preposition в is used to denote time, so it is necessary to do exercises to distinguish the cases when these two cases are used (Мама приедет (когда?) в среду "Mother will arrive on Wednesday" -Мы будем сдавать экзамены (когда?) в январе "We will take exams in January". Пушкин родился (когда?) в тысяча семьсот девяносто девятом году 'Pushkin was born in seventeen ninety-ninth").
In addition, the accusative should be used when answering questions как долго? (Они решали эту проблему целую неделю "They solved this problem for a week". Я не спал всю ночь "I stayed up all night') and как часто? (Каждую неделю мы пишем диктанты "Every week we write dictation"). If a numeral is used to indicate duration (как долго?) as a specific number of minutes, hours, etc., a numeral is put in the accusative case. Thus in sentences with imperfective verbs used accusative without the preposition -Вчера я делал домашнее задание три часа "I did my homework for three hours yesterday". And after the perfect verbthe accusative with the preposition за -Вчера я сделал домашнее задание за три часа 'I have done my homework in three hours yesterday"..
To denote the time with the accusative case, the preposition на can be used in the following cases: 1) in determining the period of time during which something will continue (на какое время?) -Я хочу взять отпуск на неделю 'I want to take a vacation for a week". В понедельник я уезжаю в командировку в Санкт-Петербург на две недели 'On Monday I'm going on a business trip to St. Petersburg for two weeks".
But these cases of the use of the accusative case can be studied only in strong groups, since they are not frequent.

Dative
In the linear and concentric study of the case system it is advisable to enter the meanings of the dative case starting with use cases without prepositions. Studying it, the case endings of nouns, adjectives, pronouns in the singular and plural forms are assimilated. The most common meaning of the dative case without preposition is meaning of recipient (Я звоню другу, сестре "I'm calling a friend, a sister"). This meaning is realized in combination with verbs звонить -позвонить, писать -написать, говорить -сказать, давать -дать, помогать -помочь and other verbs after which the question кому? is asked. These verbs are very relevant, so almost immediately there is a need for the construction of such phrases with the dative case.
The dative case denotes age (Брату семь лет "Brother is seven years old"). This meaning does not make difficulties because students learn and memorize it at the very beginning of the lessons, when they learn to speak about themselves and their family.
Exactly in this order you can study this meaning in a linear approach, but in the concentric study of the case case system, this meaning is better to start studying with more relevant constructions which express necessity with надо, нужно, можно, нельзя, etc. These impersonal sentences are necessary in many situations of communication.
Impersonal construction with the verb нравиться are more difficult because there is a simpler construction я люблю. The construction with the verb хотеться is also not the most relevant because there is an easier way to express the meaning with the phrase я хочу. Understanding the difference between мне нравится and я люблю, мне хочется and я хочу requires a more advanced level of learning Russian.
At the same advanced stage it is possible to enrich the meaning of the logical subject in impersonal sentences by words denoting the state of person (холодно, жарко, etc.).
Meanings of the dative case with prepositions also need to begin with exploring the main meaning of the dative with the preposition кpurpose of movement: the person and the object as a purpose of motion (Я иду к врачу "I'm going to the doctor"; Я подошел к окну "I come to the window").
It is necessary to repeat and further consolidate the use of various case forms with verbs of motion at this stage: opposite questions куда? (accusative) and откуда? от кого? (genitive) now receive a logical addition in the form of a question к кому? and the dative forms: Ахмед идет (куда?) в больницу (к кому?) к врачу "Ahmed goes (where?) to the hospital (to whom?) to a doctor". -Ахмед идѐт (откуда?) из больницы (от кого?) от врача "Ahmed is coming (from where?) from the hospital (from whom?) from the doctor". It is necessary to practice the use of three different cases with different prepositions on a large number of examples. It is desirable that the exercises are accompanied by illustrations for greater clarity and ease of understanding and memorization.
Further information about the use of verbs of motion with case forms is replenished by the meaning of the dative case with a preposition по the place of movement, the surface along which a movement proceeds (Студент идѐт по коридору "A student is walking down the hall). This meaning in the concentric approach should be introduced at an advanced stage of study, as in this case, students meet again the question где?, which they are already accustomed to associate with the prepositional case, so this use causes difficulties. Students need to be given an understanding of the difference between the purpose of the movement and the place where it occurs, this also requires exercises with examples that include both meanings expressed in different cases:Мария идет по парку в школу на урок "Maria is walking in the park to school to class"; Он идѐт по улице в больницу к врачу "He walks down the street to the hospital to the doctor"; Он едет по проспекту из больницы от врача "He's driving down the Avenue from the hospital from the doctor".
True enough, the value of the dative means of communication with the preposition по the question is по чему? necessary in everyday life: Он говорит по телефону "He is talking on the phone"; Я смотрел фильм по телевизору "I watched a movie on TV"; Она слышала новость по радио "She heard the news on the radio".
The dative case with the preposition по (question какой?) is also important for students to denote the meaning in combination with the names of sciences: Учебник, экзамен, пятѐрка по физике "Textbook, exam, five in physics". Other meanings are less necessary because there are other ways to express them: 1) The reason for an action with prepositions по and благодаря, question почему?: Он не пришѐл по болезни 'He did not come because disease"; Я успел благодаря будильнику "I did it thanks to the alarm clock". Constructions with meaning of reason (не пришѐл по болезни) have book character: To denote the reason, the construction with the genitive with the preposition из-за is also used, which is more frequent in Russian (не пришѐл из-за болезни).
2) The time when a repeated action takes place, the question когда?: Он ходит в спортзал по субботам 'He goes to the gym on Saturdays'. This meaning can be expressed differently, for example, the construction with the word каждый and the accusative case is more often used: каждую субботу "every Saturday".

Instrumental
The order of studying the meanings of instrumental case depends on their relevance. The meanings of association or joint action is always studied first. (Я разговариваю с другом "I'm talking to a friend"; Он пошѐл в кино с подругой "He went to the cinema with a girlfriend"), because it is very popular in everyday speech of students. English speakers learn it quite easily by analogy with the English preposition "with". This prepositional use is studied before non-prepositional ones. After it, all cases of using the instrumental case without a preposition are considered and only then the remaining cases of using with prepositions are studied.
Very frequent is the use of the instrumental case with verbs заниматься, интересоваться, увлекаться and the question чем? (Я занимаюсь спортом "I do sports"; Он увлекается музыкой "He enjoys music"; Она интересуется физикой "She's interested in physics"). However, when studying concentric at the initial level, you should limit yourself to the verb заниматься. Only then the verbs интересоваться, увлекаться are added to the verb заниматься, because the difference between the meanings of these verbs needs to be explained later, at a more advanced level.
The use of the instrumental case with the verb быть, стать, становиться, работать (кем?) to denote occupation, profession, position, etc. is also very relevant, as students learn to give information about their family and about themselves at the very initial level of learning Russian (Он будет врачом "He will be a doctor"; Мой брат станет врачом "My brother will be a doctor"; Он становится сильным "He becomes strong"; Отец работает инженером "My father works as an engineer").
The instrumental case is used to denote the instrument of action with the question чем? (Я пишу ручкой "I write with a pen"). Using this meaning is difficult because students mistakenly use the preposition C in these constructions. It is necessary to give more exercises on comparison of designs of type рисовал карандашом "painted with a pencil" -рисовал с другом "painted with a friend".
One of the most important meanings of instrumental case is denoting the agent in passive constructions, the question is кем? (Работа написана студентом "The work is written by a student"). This meaning is used in passive constructions, so short passive participles are studied in parallel. Exercises on comparison of active constructions with accusative case of direct object (Художник нарисовал картину "The artist painted a picture") and passive constructions with instrumental case denoting the agent of action (Картина нарисована художником "The picture is drawn by the artist") are productive.
The preposition с in combination with the instrumental case also denote presence of something: 1) the feature of the object: Она пьет кофе с молоком "She drinks coffee with milk"; Я люблю чай с сахаром "I like tea with sugar"; 2) the feature of the person: Мне нравится девушка с голубыми глазами "I like the girl with blue eyes".
Studying this meaning, you need to remember the genitive case since it is the opposite of the meaning of the construction with the preposition без (вода без газа -вода с газом "water without gas -water with gas").