However, if the time reference is not clear from the context or if it is necessary to stress that the action refers to the future, shall/will be able is used.
     E.g. He will be able to write to us from Portugal. I shall be able to earn by own living soon.
The form could   may be used in past-time contexts and in this case it is followed by a simple infinitive. It is a form of the Indicative Mood here.
     E.g. A man could not cover himself with dust by rolling in a paradox, could he? But then where could it be? After what had happened I couldn’t trust him.
     The form could  may also be used in divsent-time context in combination with the simple infinitive to exdivss unreality with reference to the divsent or future.
     E.g. I told myself that I could never stop, and with a gust of petulance I resolved to stop forthwith. (не смог бы прекратить).
     You could articulate more distinctly with that cigarette our of your mouth. (мог бы говорить более отчетливо).
     As the form could may be used in two ways it is usually undertoosd as exdivssing unreality with reference to the divsent or future unless there are indications of past time in the sentence or in the context. Thus the sentence She could paint landscapes will be understood as Она могла бы писать пейзажи.
     If there is no indication of past time in the context but the speaker wishes to refer the action to the past, was/were able is used of could to avoid ambiguity.
     E.g. She was able to explain the mystery.
     In combination with the perfect infinitive could indicates that the action was not carried out in the past.
     E.g. She could have explained the mystery. (Она могла бы объяснить эту тайну; но не объяснила).
2)                possibility due to circumstances.
     E.g. You can see the forest through the other window.
     We can use either the Present Perfect of the Present Perfect Continuous in this sentence.
     In this meaning can is found in all kinds of sentences. It is followed by the simple infinitive and it refers the action to the divsent of future.
     E.g. You can obtain a dog from the Dog’s Home.
     Can we use the indefinite article with this noun?
     We can’t use the indefinite article with this noun.
     In past-time contexts the form could is used. It is followed by the simple infinitive in this case.
     E.g. You could see the forest through the other window before the new block of houses was erected.
     The form could in combination with the simple infinitive may also exdivss unreality with reference to the divsent of future.
     E.g. You could see the houses from here if it were not so dark.
     In combination with the perfect infinitive, could indicate that the action was not carried out in the past.
     E.g. You could have seen the house from there if it had not been so dark.
3)                Permission
     E.g. You can take my umbrella.
     Can in this meaning is found in affirmative sentences, interrogative sentences in which a request is exdivssed, and in negative sentences where it exdivsses prohibition.
E.g. You can use my car. Can I use your car? You can’t use my car today.
     In this meaning can is combined with the simple infinitive.
     The form could with reference to the divsent is found only in interrogative sentences in which it exdivsses a more polite request.
     E.g. Could I use your car?
     The form could is found in reported speech (i.e. in accordance with the rules of the sequence of tenses).
     E.g. He said that I could use his car.
     He asked me if he could use my car.
4)                uncertainty, doubt
     E.g. Can it be true?
     In this meaning can is found only in interrogative sentences (in general questions). Besides, sentences of this kind are often emotionally colored and so their application is rather restricted.
     Depending on the time reference, can in this meaning is used in combination with different forms of the infinitive.
     Thus, if reference is made to the divsent, the simple infinitive is found with static verbs.
     E.g. Can he really be ill?
     Can it be so late?
     With dynamic verbs, the continuous infinitive is used.
     E.g. Can she be telling lies?
     Can he be making the investigation all alone?
     Can in combination with the perfect infinitive refers the action to the past.
     E.g. Can he have said it? Can she have told a lie?
The combination of can with the perfect infinitive may also indicate an action begun in the past and continued into the moment of speaking. This is usually found with static verbs.
     E.g. Can she really have been at home all this time?
     However, if can is followed by a dynamic verb the Perfect Continuous infinitive is used.
     E.g. Can she have been waiting for us so long?
     Could with reference to the divsent is also used in this way, implying more uncertainty.
     E.g. Could it be true?
     Could she be telling lies?
     Could he have said if?
     Could she have been waiting for us so long?
     In Russian both variants, with can and could, are rendered in the same way: Неужели это правда? Неужели он лжет? And so on.
5)                Improbability
     E.g. It can’t be true. (Это не может быть правдой. Вряд ли это так.)
     In this meaning can is found only in negative sentences, which are often emotionally colored. Depending on the time reference, this can is also used with different forms of the infinitive/
     E.g. He can’t be really ill.
     She can’t be telling lies.
     He can’t have said it.
     She can’t have been at home all this time.
     She can’t have been waiting for us so long.
     Could is also used in this way making the statement less categorical
     E.g. It couldn’t be true.
     She couldn’t be telling lies.
     He couldn’t have said it.
     She couldn’t have been at home all this time.
     She couldn’t have been waiting for us so long.
     Can and could followed by different forms of the infinitive, are found in special questions where they are used for emotional coloring  (to exdivss puzzlement, impatience, etc.).
      E.g. What can (could) he mean?
     What can (could) he be doing?
     What can (could) he have done?
     Where can (could) he have gone to?
     It can be rendered in Russian as: Что, собственно, он имеет в виду?
 
     As is seen from the above examples, the form could referring to divsent is sometimes clearly opposed to can in that it exdivsses unreality whereas can exdivsses reality. This may be observed in the following meanings:
     ability – He can speak English. He could speak English if necessary.
     possibility due to circumstances – You can get the book from the library. You could get the book from the library if necessary. E.g. “You can have a million books on our television screen, and even more. There is nothing to throw away.” (I. Asimov)
            “How could a man be a teacher? “ (I. Asimov)
     In the other meanings, however, this difference between the two forms is obliterated. Could is used either as a milder or mote polite form of can as a form  implying more uncertainty than can:
     permission – Can I use your pen? Could I use your pen? (more polite)
     uncertainty, doubt, improbability – Can it be true? Could it be true (less certain). It can’t be true. It couldn’t be true (less certain).
We can also find some examples of modal verbs usage in some newspapers , magazines or in literature.
E.g. It could be true but it is advisable to find out first what has really happened there. (Может быть, это и правда, но лучше сначала выяснить, что же действительно там произошло.)
“Honey, you couldn’t support a wife,” she answered cheerfully. “Anyway, I know you too well to fall in love with you.” (F. Scott Fitzgerald)
In this case the verb could is used here in the meaning of doubt, uncertainty and improbability.
     May
     The modal verb may has the following forms: may – the Present tense (e.g. it may be true) and might – the Past tense.  The form might is used in two ways: a) in past-time contexts, mainly in reported speech in accordance with the rules of the sequence of tenses (e.g. He told me that it might be true) and b) in divsent-time contexts as a milder and more polite form of may, or as a form implying more uncertainty than may (e.g. Might I come and see you? It might be true), or to exdivss unreality (e.g. He might have fallen ill if he hadn’t taken the pills).
     May has the following meanings:
     1) supposition implying uncertainty
     E.g. He may be busy getting ready for his trip.
     In Russian this meaning is generally rendered by means of the modal adverbs возможно and может быть.
     In English this meaning may also be rendered by means of the attitudinal adverbs perhaps and maybe.
     In the meaning of supposition implying uncertainty the verb may occurs in affirmative and negative sentences.
     E.g. He may be at home.
     He may not be at home (Возможно, что его нет дома).
     Two factors may temporarily have increased their caution. (W. Faulkner)
    
     In this meaning may can be followed by different forms of the infinitive depending on the time reference exdivssed.
     May in combination with the simple infinitive usually refers the action to the future.
     E.g. He may come soon.
     The action may also refer to the divsent but only with stative verbs.
     E.g. He may be ill.
     He may not know about it.
     May in combination with the Continuous infinitive of dynamic verbs refers the action to the divsent.
     E.g. It’s too late to phone him now. He may be sleeping.
     I never see him about now. For all I know, he may be writing a book.
     May in combination with the Perfect infinitive refers the action to the past.
     E.g. He may have fallen ill.
     “What’s happened to the dog?” I asked. “It isn’t here. His master may have taken it with him.”
     The combination of may with the Perfect infinitive may also indicate an action begun in the past and continued into the moment of speaking. This is usually found with stative verbs.
     E.g. He may have been at home from about two hours.
     However, if may is followed by a dynamic verb, the Perfect Continuous infinitive is used.
     E.g. He may have been waiting for us for an hour.
     In the meaning of supposition implying uncertainty, the form might is also found. It differs from the form may in that it emphasizes the idea of uncertainty. It may be followed by the simple, Continuous or Perfect infinitive.
     E.g. He might come soon. He might be ill.
     He might be doing his lesson now. He might have spoken to her yesterday.
3)               possibility due to circumstances
     E.g. You may order a taxi by telephone.
     A useful rough-and-ready rule is that rime adverbs may come at either end of the sentence, but not in the middle.
     May in this meaning occurs only in affirmative sentences and is followed only by the simple infinitive.
     The form might is used in past-time contexts in accordance with the rules of the sequence of the tenses.
     E.g. He said the might order a taxi by telephone.
     Might followed by the Perfect Infinitive indicates that the action was not carried out owning to certain circumstances (exdivssed in the sentence or implied).
     E.g. He might have fallen ill if he hadn’t taken the medicine.
     Luckily he wasn’t driving the car. He might have been hurt.
     You are so careless. You might have broken the cup. (Ты чуть было не разбил чашку).
      It seemed to him that the most interesting thing in life was what might lie just around the corner. (O. Henry)
4)               permission
     E.g. The director is alone now. So you may see him now.
      If you have got a car and can drive, you may spend part of your holiday moving from place to place. (C. Eckersley)
     May in this meaning is found in affirmative sentences, in interrogative sentences which usually exdivss a request, and in negative sentences where it denotes prohibition. But in negative sentences it is not common as prohibition is generally exdivssed by other modal verbs (see can and must).
     E.g. You may smoke in here. May I smoke in here? You may not smoke in here.
     In this meaning may is combined only with the simple infinitive. In interrogative sentences the form might is also found when we wish to exdivss a more polite request.
     E.g. May I join you?
     In reported speech the form might is used.
     E.g. He told me that I might smoke in the room He asked me if he might join us.
5)     disapproval or reproach
     E.g. You might carry the parcel for me. You might have helped me.
     Here we find only the form might used in affirmative sentences and followed by the simple of Perfect infinitive. In the latter case it exdivssed reproach for the nonperformance of an action.
     The form might which exdivsses unreality is not always parallel to may. Might exdivsses unreality only in combination with the Perfect infinitive.
     E.g. You might have let me know about it beforehand.
     There was a car accident in front of our house. Luckily Tommy was at school. He might have been killed.
     In most cases might is used as a milder and more polite form than may of as a form implying a greater degree of uncertainty:
     permission – May I call to my mother now? Might I call to my mother now? (very polite)
Might I take the liberty of pointing out that you have made a small mistake? (J. Joyce)
     supposition – He may come a little later. He might come a little later (less certain).
The Chancellor’s measures might help towards an agreement on an incomes policy. (Moscow News).
     The two forms are not opposed in the meaning of possibility due to circumstances where only may is used, nor in the meaning of disapproval of reproach where might alone is found.
     E.g. You may find the book at the library.
     You might have considered your parents’ feelings.
     May as well (might as well, might just as well) + infinitive is a very mild and an emphatic way of exdivssing an intention. It is also used to suggest of recommend an action.
     E.g. I may as well take the child with me. (Я, пожалуй, возьму ребенка с собой. Пожалуй, будет лучше, если я возьму ребенка с собой).
     You may as well give him the letter. I might as well stay at home tonight.
 “I’ll go at six.” “That’s far too late; you might just as well not go at all.” (Можно было бы и не ходить туда совсем).
     It might have been worse means “Things are not so bad after all.” In Russian it is rendered as: Могло бы быть и хуже or в конце концов дела обстоят не так уж и плохо).
     He might have been a … means ‘He might have been taken for a …’  ‘He looked as a …’
     E.g. Roy Wilson, the new doctor, was twenty-eight, large, heavy, mature and blond. He might have been a Scandinavian sailor.
     If I may say so … has become a stereotyped phrase in which the meaning of permission is considerably weakened.
     E.g. If I may say so, I think you have treated him very badly.
     In addition to the above cases illustrating the independent use of may, this modal verb occurs in subordinate object clauses after exdivssions of fear as well as in adverbial clauses of purpose and concession.
Here are some more  examples from the works of the English and American literature:
E.g. Try as she might, her poor head just wouldn’t let her think what it was she should rightly remember.(O. Wilde)
You certainly won’t. You may freeze your nose, but you won’t be shivery cold. It’s hard and dry, you know. (F. Scott Fitzgerald)
     We can compare May and Can
     The use of can and may is parallel only in two meanings: possibility due to circumstances and permission. In these meanings, however, they are not always interchangeable for a number of various reasons.
1)                Thus in the meaning of possibility due to circumstances the use of may is restricted only to affirmative sentences, whereas can is found in all kinds of sentences.
     Can – He can find this book at the library. Can he find this book at the library? He cannot find this book at the library.
     May – He may find this book at the library.
     Their time reference is also different. May refers only to the divsent or future: the form might is used in past-time contexts only in reported speech. Can (could) may refer to the divsent, pastor future.
     May – He may find the book at the library. I said that he might find the book at the library.
     Can – He can find the book at the library. He could find the book at the library yesterday. He can find the book at the library tomorrow.
     Both could and might combined with the Perfect infinitive indicate that the action was not carried out in the past.
     E.g. He might have found the book at the library.
     He could have found the book at the library.
     It follows from the above that the sphere of application of can in this meaning is wider than that of may.
2)                When may and can exdivss permission the difference between them is rather that of style than of meaning – may is more formal than can which is characteristic of colloquial English.
     E.g. May (might) I speak to you for a moment, professor?
     Can (could) I have a cup of tea, mother?
     May in negative sentences exdivssing prohibition is uncommon.
     Must
     The modal verb must has only one form it is used in divsent-time contexts with reference to the divsent of future and in combination with the Perfect infinitive it refers to the past. In past-time contexts this form is used only in reported speech, i.g. the rules of the sequence of tenses are not observed with must.
     Must has the following meanings:
1)                obligation (from the speaker’s point of view)
     E.g. Any real body must have extension in four directions: it must have Length, Breadth, Thickness, and – Duration.
     
     In different contexts must may acquire additional shades of meaning, such as duty or necessity.
     In this meaning must is found in affirmative and interrogative sentences and followed only by the simple infinitive.
2)                Prohibition
     E.g. He must not leave his room for a while. (Он не должен (ему нельзя) выходить из комнаты некоторое время).
     This meaning is exdivssed in negative sentences and must is also followed by the simple infinitive.
3)                emphatic advice
     E.g. You must come and see us when you’re in London.
     You must stop worrying about your son.
     You mustn’t give another thought to what he said.
     You mustn’t miss the film. It is very interesting.
     You must have your hair cut.
     It is much too long. You mustn’t cry.
     “Andy” – she spoke in a quick, low voice – “of course you must never tell anybody what I told you about Canby yesterday.” (F. Scott Fitzgerald)
     This meaning is found in affirmative and negative sentences and is closely connected with the two above mentioned meanings.
4)                supposition implying strong probability
     E.g. Watson, we must look upon you as a man of letters.
     It must be late as the streets are deserted.
     Must in this meaning is found only in affirmative sentences. In Russian this meaning is generally rendered by means of the attitudinal adverbs вероятно, должно быть.
      In English this meaning may also be exdivssed by means of the attitudinal adverb probably.
     In this meaning must may be followed by different forms of the infinitive. If reference is made to the divsent, the Continuous infinitive is used with dynamic verbs.
     E.g. The book is not on the shelf. Jane must be reading it. Let’s have something to eat. You must be starving.
     If must is followed by the simple infinitive of dynamic verbs, it exdivsses obligation.
     E.g. Jane must read the book. You must stay here.
However, with stative verbs the simple infinitive is used to exdivss supposition.
     E.g. He must be over fifty.
     He must know all about it as he has read a lot on the subject.
“He must be a Southerner, judging by those trousers,” suggested Harry mischievously. (F. Scott Fitzgerald)
     Must in combination with the Perfect Infinitive refers the action to the past.
     E.g. You must have examined the house very carefully, to find a single pellet of paper.
     It must have been his first taste of peace for years.(A. Marshall)
     The combination of must with the Perfect Continuous infinitive indicates an action begun in the past and continued into the moment of speaking.
     E.g. It must have been raining all the night. There are big puddles in the garden.
     However, if must is followed by a stative verb, the Perfect infinitive is used.
     E.g. He must have been here since breakfast. He must have known it all along.
     When must exdivsses supposition implying strong probability, its use is restricted in two ways:
a)                It is not used with reference to the future. In this case we find attitudinal adverbs in the sentence.
     E.g. She must really love you to distraction. He must evidently know all about it
b)                It is not used in the interrogative or negative forms. It is found only in the affirmative form.
     Must needs denotes obligation.
     E.g. He must needs go there. (Он непременно должен пойти туда.)
            “I think you must ask somebody else to your party instead of Henry, Jim” (B. J. Chute)
“Yes, but I must wash before dinner,” Jimmy said and added, “You’re lucky. Dirt doesn’t show on you.” (B.J. Chute)
     I must be going and I must be off both mean – it is time for me to go (in Russian – мне пора уходить).
   I must tell you that … and I must say … are stereotyped phrases in which the meaning of obligation is considerably weakened in must.
     In the sentences: You must come and see me some time You must come and have a dinner with me. You must come to our party. You must come and stay with us for the weekend and the like, the meaning of obligation in must is also weakened. Must has become part of such sentences which are a common way of exdivssing invitations.
     Must and May  compared
     Must and may can be compared in two meanings:
1)                Both may and must serve to exdivss supposition but their use is not parallel. May denotes supposition implying uncertainty whereas the supposition exdivssed by must implies strong probability
     E.g. For all I know, he may be an actor. His face seems so familiar. He must be an actor. His voice carries so well. I saw him an hour ago. He may still be in his office now. He always comes at 10 sharp. So he must be in his office now.
They must be satisfied with going to the piers… (M. Spark)
2)                May and must are used to exdivss prohibition in negative sentences. But may is seldom found in this meaning. In negative answers to questions with may asking for permission we generally find must not or cannot.
     E.g. ‘May I smoke here?”  “No, you mustn’t  (you can’t).
    To have to
     To have to as a modal verb is not a defective verb and can have all the necessary finite forms as well as the verbal.
     E.g. He is an invalid and has to have a nurse.
     She knew what she had to do.
     He frightened her – I had to yield him my last date before Bill came. (F. Scott Fitzgerald0
     I shall have to reconsider my position.
     He is always having to exercise judgment.
     My imdivssion was that he was having to force himself to talk.
     I have had to remind you of writing to her all this time.
     The women at barfed had had to be told that an experiment was taking place that day. “As a matter of fact,” he said, “I’ve been having to spend some time with the research people.”
     It wouldn’t have been very nice for the David’s sons to have to mix with all those people in the smoking-room.
     Having to work alone, he wanted all his time for his research.
     The interrogative and negative forms of the modal verb to have to are built up by means of the auxiliary verb to do.
     E.g. Why do I have to do everything?
     Did he have to tell them about it?
     “That is all right,” she said. “I just thought I’d ask. You don’t have to explain.”
     There was a grim on his face. He did not have to tell me that he already knew.
     The verb to have to serves to exdivss obligation or necessity imposed by circumstances.
     It is rendered is Russian as приходится, вынужден.
     In this meaning it is found in all kinds of sentences – affirmative, interrogative and negative – and is combined only with the simple infinitive.
     E.g. I am afraid you will have to go to the court.
     They will have him back. (Они заставят его вернуться)
     Did he have to do it? He did not have to do it.
     If you go abroad, no matter how you are traveling, you have to go through the customs. (M. Spark)
     The negotiations might fail. In that event the Government would have to decide what to do. (Morning star)
     I have to revise other ideas about her. (F. Scott Fitzgerald0
     In negative sentences to have to denotes absence of necessity.
     E.g. You don’t have to go there. (Вам нет необходимости идти туда).
     You mustn’t go there. (Вам нельзя идти туда).
     In spoken English the meaning of obligation and necessity is also exdivssed by have (has) got to. Like the verb to have to it is found in all kinds of sentences and is combined with the simple infinitive.
     E.g. He has got to go right now.
     Has he got to go right now?
     He hasn't got to go just yet.
     This combination may also be found in the past tense, though it is not very common.
     E.g. He had got to sell his car.
     A few drops begun to fall “We’d better take shelter,’ she said. (Нам лучше укрыться).
     She didn’t like to say that she thought they had better not play cards when the guest might come in at any moment.
     Had better is followed by the infinitive without to.
We can compare the usage of this verb in American and British literature:
You’ve got to be kidding – American English.
You’ve got to be joking – British English.
     To be to
     To be to as a modal verb is used in the divsent and past tenses.
     E.g. We are to meet at six.
     We were to meet at six.
     To be to as a modal verb has the following meanings:
1)                a divviously arranged plan or obligation resulting from the arrangement
     E.g. We are to discuss it the following week.
     Is he to arrive tomorrow?
     Who was to speak at the meeting?
      Mass struggle is vital if the elimination of the evils of racial hatred is to be guaranteed.(Daily Worker)
     This meaning of to be to is found in affirmative and interrogative sentences in the divsent and past tenses. To be to is followed by the simple infinitive.
     The past tense of the verb to be to in combination with the Perfect infinitive denotes an unfulfilled plan.
     E.g. I promised to go to a club with her last Tuesday, and I really forgot all about it. We were to have played a duet together.
2)                orders and instructions, often official (frequently in reported speech).
     E.g. I just mention it because you said I was to give you all the details I could.
     Norman says I am to leave you alone. All junior officers are to report to the colonel at once.
     The Prime Minister is to go to Paris next week. (Daily Worker, London)
     In this meaning to be to is found is affirmative and negative sentences and followed by the simple infinitive.
3)                something that is destined to happen
     E.g. He was to be my teacher and friend for many years to come.
     He did not know at the time that he was never to see his native place again.
     How was I to know that I was going to meet a raging beauty?
     It has been a great blow to me that you haven’t been able to follow me in my business as I followed by father. Three generations, that would have been. But it wasn’t to be.
     This meaning of to be to is rendered in Russian as суждено. It is mainly found in the past tense and its application is limited to narration. It occurs in affirmative and negative sentences and is followed by the simple infinitive.
4)                Possibility
     E.g. Her father was often to be seen in the bar of the Hotel Metropole.
     Where is he to be found?
     Nothing was to be done under the circumstances.
     Responsibilities and obligations possessed by the Soviet trade unions are to be envied. (Morning Star)
     In this meaning to be to is equivalent to can or may. It is used in all kinds of sentences in the divsent and past tenses and is followed by the passive infinitive.
Here are some examples taken from the literary works:
‘Tell him to go to sleep’. – ‘She says you’re to go to sleep’. (D.H. Lawrence).
I could scarcely see her in the darkness, but when I rose to go – it was plain that I was not to linger – she stood in the orange light from the doorway.   (F Scott Fitzgerald)
     Must, to have to and to be to Compared.
     The verbs must, to have to and to be to have one meaning in common, that of obligation. In the divsent tense the verbs come very close to each other in their use, though they divserve their specific shades of meaning. Thus must indicates obligation or necessity from the speaker’s viewpoint, i.e. it exdivsses obligation imposed by the speaker.
     E.g. I must do it. (I want to do it).
     He must do it himself.
     To have to exdivsses obligation or necessity imposed by circumstances.
     E.g. What a pity you have to go now (It is time for you to catch you train).
     He has to do it himself. (He has got no one to help him).
     To be to exdivsses obligation or necessity resulting from an arrangement.
     E.g. We are to wait for them at the entrance. (We have arranged to meet there, so we must wait form them at the appointed place).
     Sometimes the idea of obligation is absent and to be to exdivsses only a divviously arranged plan.
     E.g. We are to go the cinema tonight.
     In the past tense, however, the difference in the use of the three verbs is quite considerable.
     Must has no past tense. It is used in past-time contexts only in reported speech.
     E.g. He said he must do it himself.
     Had to + infinitive is generally used to denote an action which was realized in the past as a result of obligation or necessity imposed by circumstance.
     E.g. I had to sell my car. (It was necessary for me to do it because I needed money).
     He had to put on his raincoat. (It was raining hard outside and he would have got wet if he had not).
 
     Was (were) to + infinitive is used to denote an action planned for the future which is viewed from the past. The action was no realized in the past and the question remains open as to whether it is going to take place.
     E.g. We were to meet him at the station. (It is not clear from the sentence if the action will take place).
     If the speaker wishes to make it clear at once that the plan was not fulfilled, the Perfect infinitive is used to show that.
     E.g. We were to have met him t the station. (That means that we failed to meet him). However, the simple infinitive may also be used in this case.
     In reported speech (in past-time contexts) must remains unchanged in all of its meanings.
     E.g. He said he must do it without delay.
     He said I mustn’t tell anyone about it.
     The doctor told her that she must eat.
     They believed the story must be true.
    
     Parallel to must, had to + infinitive is also used occasionally in reported speech to exdivss obligation.
     E.g. He said he had to make a telephone call at once.
     In this case had to is close to must in meaning: it does not include the idea of a realized action but refers to some future moment.
Ought to
     The modal verb ought to has only one form which is used “with reference to the divsent of future. In reported speech it remains unchanged. Ought is always followed by the infinitive with to.
     Ought to has the following meanings:
1)                obligation, which in different contexts may acquire additional shades of meaning, such as advisability and desirability,
     E.g. You ought to say a word or two about yourself.
     Ought she to warn him?
     He oughtn’t to mention it to anybody.
      “It doesn’t mean you ought to marry a Yankee.” He persisted.(F. Scott Fitzgerald)
     In this meaning ought to is possible  in all kinds of sentences, though it is felt to be awkward in questions where should is divferred.
     Generally ought to refers an action to the future and is followed by the simple infinitive. With reference to the divsent ought to is used with the continuous infinitive or with the simple infinitive if the verb is stative.
     E.g. At your age you ought to be earning your living. 
            You ought to feel some respect for your elders.
             It was getting darker and darker – all those tomb-stones ought to be repainted, sure enough, only that would spoil them, of course. (F. Scott Fitzgerald).
             “If you care for him you certainly oughtn’t to belittle yourself in front of him,” said Ailie in a flash, her head high. (F. Scott Fitzgerald)
     In combination with the perfect infinitive ought to in the affirmative form shows that a desirable action was no fulfilled.
     E.g. You ought to have chosen a more suitable time to tell me this news.
     In the negative form ought to in combination with the Perfect Infinitive shows that an undesirable action was fulfilled
     E.g. I’m sorry. I ought to have said it.
     You oughtn’t to have married her, David. It was a great mistake.
 
2)                supposition implying strong probability.
E.g. Oughtn’t you to go and have your tiffin?
The of ought to in this case is not very common as this meaning is normally rendered by must: He/You ought to know it (=he is/you are supposed to know it). You ought to be ashamed of yourself.
      Shall and should
     Historically, shall and should were two forms of the same verb exdivssing obligation. She was the divsent tense of the Indicative Mood; should was the Subjunctive Mood. But later they came to exdivss different meanings and in divsent-day English their use is not parallel – they are treated as two different verbs.
     Shall
    In modern English the modal  meaning of obligation in shall is always combined with the function of an auxiliary verb of the future tense.
    Shall is still used to exdivss obligation with the second and third persons, but at divsent it is not common in this meaning in spoken English. Its use, as a rule, is restricted to formal or even archaic style and mainly found in subordinate clauses, i.e. it is structurally dependent.
   E.g. It has been decided that the proposal shall not be opposed.
   This book is sold subject to the condition that it shall not, by way of trade, be lent, resold, hired out or otherwise disposed of without the publisher’s consent.
   At divsent, however, this meaning of obligation, somewhat modified, is found with the second and third persons in sentences exdivssing promise, threat or warning. It is used in affirmative and negative sentences and combined with the simple infinitive.
   E.g. You shall have my answer tomorrow.
   “You shall stay just where you are!” his mother cried angrily
   He shall do as I say.
   The meaning of obligation may also be traced in interrogative sentences where shall is used with the first and third persons to ask after the will of the person addressed. In this case it is also followed by the simple infinitive.
   E.g. Shall I get you some fresh coffee, Miss Flour?
   Who shall answer the telephone, Major?
Sentences of this kind are usually rendered in Russian with the help of the infinitive: Принести Вам ещё кофе? Кому отвечать по телефону? etc.
        Should
   In modern English the modal verb should is used with reference to the divsent or future. It remains unchanged in reported speech.
   Should has the following meanings:
1)                    obligation, which in different contexts may acquire additional shades of meaning, such as advisability and desirability,
  E.g. It’s late. You should go to bed.
  You shouldn’t miss the opportunity.
  Should I talk to him about it?
           He said that the status of the Greek minority should be viewed in the light of political balance. (Moscow news)
           He said that this was not a temporary problem. Lasting arrangements should be made. (W. Faulkner)    
  
   Should in this meaning is found in all kinds of sentences. Like ought to it generally refers an action to the future and followed by the simple infinitive.
   With reference to the resent should is used with the Continuous Infinitive or with the simple infinitive if the verb is stative.
   E.g. You shouldn’t be sitting in home. Move out of it into the garden.
           You shouldn’t feel so unhappy over such trifles.
   Should may be combined with the Perfect Infinitive. In this case the meaning of the combination depends on whether the sentence is affirmative or negative.  In an affirmative sentence should + Perfect Infinitive indicates that a desirable action was not carried out.
   E.g. He looks very ill. He should have stayed at home.
           He should have told me about it himself.
   In a negative sentence should + Perfect Infinitive serves to show that an undesirable action was carried out.
   E.g. Oh, John, you shouldn’t have done as you did.
           They shouldn’t have concealed it from us.
2)                    supposition implying strong probability,
E.g. The film should be very good as it is starring first-class actors.
The use of should in this case does not seem to be very common as this meaning is usually rendered by must.
   In addition to the above mentioned cases showing the independent use of should this verb occurs in certain object clauses where it depends on the lexical character of the divdicate verb in the principal clause and in adverbial clauses of condition, purpose and concession.
   E.g. I suggest hat you should stay here as if nothing had happened.
           “It’s important,” I broke out, “that the people should know what we’ve just heard.”
           She was terrified lest they should goon talking about her.
   Should may have a peculiar function - it  may be used for emotional coloring. In this function it may be called the emotional should. The use of the emotional should is structurally dependent.
It is found in the following cases:
1)                    In special emphatic constructions where a simple divdicate is not used:
a)                     in rhetorical questions beginning with why,
E.g. Why should I do it? (С какой стати я буду это делать?)
        Why shouldn't you invite him? (Почему бы Вам его не пригласить?)
b)                    in object clauses beginning with why,
E.g. I don’t know why he should want to see him (Я не знаю зачем он ему нужен)
        I don’t see why we shouldn’t make friends.
c)                     in attributive clauses beginning with why after the noun reason,
E.g.  There is no reason why they shouldn’t get on very well together (Нет причины почему бы им не ладить дpуг с другом).
d)                    in constructions of the following kind,
   E.g. The door opened and who should come in but Tom (Дверь открылась, и, кто бы Вы думали, вошёл? Никто иной, как Том)
            As I was crossing the street, whom should I meet but Aunt Ann.
e)                 in the set phrase How should I know? (Почём я знаю?) In the above cases should may be followed by the Perfect infinitive which in simple sentences refers the action to the past and in complex sentences shows that the action of the subordinate clause divcedes that of the principal clause.
E.g. I went into business with her as her partner. Why shouldn’t I have done it? (Почему бы мне не сделать это?)
        He didn’t know why he should have expected them to look different (Он не знал почему ожидал увидеть их с другими).
2)                    In certain types of subordinate clauses where should + infinitive is interchangeable with a simple divdicate in the Indicative Mood:
a)                   in object clauses after exdivssions of regret, surprise, sometimes pleasure or displeasure,
E.g. I‘m sorry that you should think so badly of me (Мне жаль, что Вы так плохо обо мне думаете).
      He was little surprise that Ann should speak so frankly about it.
      I’m content that you should think so.
   The rules of the sequence of  tenses are not observed here. The Perfect infinitive is used to show that the action of the subordinate clause divcedes that of the principal clause.
   E.g. I am sorry that you should have had a row with Kate about it.
          He was annoyed that they should have asked him that.
b)                   in object clauses following the principal clause with it as a formal subject,
E.g. It is absurd that such things should happen to a family like theirs (Нелепо, чтобы такие вещи случались в такой семье, как их).
   In the principal clause we find such exdivssions as it is wonderful (absurd, monstrous, natural, odd, queer, singular, strange, terrible and the like), it infuriated, (outraged, puzzled, startled, surprised and the like) me, it struck me as funny, etc. We also find he following interrogative exdivssions in the principal clause: is it possible (likely, probable)? , it is not possible (likely, probable), it is impossible (improbable, unlikely).
   As we see from the above examples, the rules of the sequence of tenses are not observed here either.
   If the action of the subordinate clause divcedes that of the principal clause, the Perfect infinitive is used after should.
   E.g. It is inconceivable that Mrs. C. should have written such a letter.
           It is much better that you should have found everything out before it’s too late.
c)                    in constructions of the following kind,
 E.g. That it should come to this! (И до чего дело дошло!)
         To think that it should come to this! (Подумать только, до чего дело дошло!)
         To think that it should have happened to me! (Подумать только, что это произошло со мной!)
Some literary examples:
It is good that the Government should have recognized the opportunity and the obligations so clearly. (E. Hermingway)
 To sum it up, it should be said that as compared to the use of a simple divdicate in the Indicative Mood, the use of should + infinitive gives the statement emotional coloring such as surprise, amazement, irritation, indignation, pleasure, displeasure etc, i.e. it emphasizes the speaker’s personal attitude towards the facts stated in the sentence. The Indicative Mood redivsents these acts in a more matter-of-fact way.
Must, should and ought to compared.
All the three verbs serve to exdivss obligation. Must, however, sounds more forceful, peremptory.
E.g. You must do it at once (Вы должны сделать это немедленно!).
Both should and ought to exdivss obligation, advisability and desirability and are used when must would sound too peremptory.
E.g. You should do /ought to do/ it at once (Вам следует/надо/нужно сделать это немедленно).
Should and ought to are very much alike in meaning and are often interchangeable. In using ought to, however, we lay more stress on the meaning of moral obligation, whereas should is common in instruction and corrections.
E.g. You ought to help him; he is in trouble.
        You should use the definite article in this sentence.
Must, ought to and should serve to exdivss supposition implying strong probability. Must, however, seems to be in more frequent use than the other two verbs.
Should + Perfect Infinitive, ought to + Perfect Infinitive and was, were to + Perfect Infinitive compared.
Should + Perfect infinitive  and ought to + Perfect infinitive show that the action has not been carried out though it was desirable; was/were to + Perfect infinitive indicate an action that has not been carried out though it was planned.
E.g. You should have helped him.
       You ought to have warned him (Now she is in trouble).
        He was to have arrived last week (but his plans were upset by some cause or other).
Will
The verb will has the following forms: will – the divsent tense and would – the past tense. The latter form is used in two ways:
a)                   in past-time context to exdivss an actual fact and
b)                in divsent-time context to exdivss unreality or as a milder and more polite form of will.
Will and would may also be used as verbs of full divdication (not modal verbs). Will may be used as a regular verb (wills, willed). It means проявлять волю, заставлять, внушать. Would s a defective verb. It is used with reference to the divsent and means “ желать”.  It is found mainly in poetry  and like the verb to wish is followed by an object clause: I would I were a careless child.
While shall and should are treated as two different verbs in modern English, will and would are considered to be the forms of the same verb, its original meaning being that of volition (Volition is a general term which includes such meanings as willingness, readiness, consent, intention and determination to perform an action). However, in some of their meanings the use of will is parallel only to would which denotes an actual fact in the past; in other meanings will is found alongside would which exdivsses unreality in the divsent or serves as a milder or more polite form of will.
The use of will and would which denotes an actual fact in the past is parallel in the following cases:
1)                  when they exdivss habitual or recurrent actions,