When speaking about the category of tense we should remember that we distinguish different tense forms on the basis of some opposition. But in a number of cases these oppositions may be reduced. It means that morphological form typical of one tense may express the meaning of some other tense. We usually observe it in definite contexts.
Ex. The form of the Present Tense may express the meaning of the Past, Future Tense in subordinate clauses of time and condition (If I see him tomorrow I will ask him to do it for you).
Besides the Present Tense may be used to express an action planned for the Future especially with verbs of motion. When dealing with the category of tense we should touch upon one more problems, which is typical of English. The problem is known as the Sequence of tenses. In English if the predicate verb in the main clause of a complex sentence is used in the past tense, the predicate verbs in the subordinate clauses саn be used in the present or future tenses. The Present tense is replaced by the Past Tense modified or not modified by the Perfect and the Future Tense is replaced by the Future-in-the-Past.
The Sequence of tenses is explained by many traditional grammars as a mechanical shift of tenses. However, this explanation can't be treated as adequate. No mechanical shift takes place.
In the events in the main and subordinate clauses are simultaneous, then the same tense forms are used. If the events of the subordinate clause precede the events of the main clause, than the predicate verb in the subordinate clause is modified by the Perfect.
In the actions the subordinate clause follow the events of the main clause, then the predicate verb takes the specific form in the Future-in-the-Past.
We observe this correlation of events only when the starting temporal center is in the Past.
But if the starting point is in the Present, no sequence of tenses is observed and we use any tense form in the subordinate clause or clauses, which is required by the logical sequence of events. So what we mean by the traditional term Sequence of Tenses that is in reality sequence of events is nothing but a synthesis of two categorical notions:
1) The category of tense which expresses the relation of the action to some moment of time.;
2) The category of perfect, which expresses the relation of actions to each other.
The Advanced English Course for Foreign Students by Brian Kelly, B.A. L., Longmans, 1980, pp. 76-91. Theme "Verb: Mood"
A. PROSE PASSAGES. (See also pars. 358-359.)
1. Unless Jim stops burning the candle at both ends, he may ruin both his health and his prospects. He is certainly going the pace. If he were able to look into the future, he would not be so wild. There is no doubt that he will go to the bad. unless he changes his ways. In any case, he will not get on in the world, if he gives way to his inclinations so easily. If he tried to control himself, and live more quietly, it would be better for him. But he is game for anything, when he is in one of his wild moods. If a young man fools away the time that he should spend in study, he cannot expect to come off with flying colours in his examinations. But Jim makes fun of steadiness, and says that if it means drudgery, hard work is not worth while. According to him, a life that did not include women, wine, and cards, would not be life at all, but mere existence. He forgets that if you do not take advantage of your opportunities while you are young, your life must necessarily be a failure afterwards. Even supposing a man like that got over his folly later, and turned over a new leaf, it would probably be too late. If you should see him, I think you ought to try to persuade him of his foolishness. You might tell him that it is a shame to see a brilliant young fellow like him making a fool of himself. If you would try, I think it might do some good. Do you think you could? Unless we lay our heads together and find some way of getting him away from the company he is keeping, he will so to the dogs altogether. But as long as he meets all attempts to help him with high words, it will be difficult even for the friends of a lifetime to have patience with him. It would be difficult to expect anybody to lend a helping hand to a man. // he persisted, as Jim does, in placing a wrong construction on everything that is said to him. If only he realized that his friends are acting for the best, it might be possible to do something for him. But if he persists in calling everybody a busybody for taking an interest in his welfare, he must not be surprised if they draw in their horns. If he keeps on in that strain, everybody will give him up as a bad job. Supposing everybody were to behave as he does, what would become of the world? He says that it would be a better place to live in; and that he would be more impressed with my remarks, did he not suspect that I speak with my tongue in my cheek. It seems that he has heard rumors of my own gay and joyous youth. All I can say is that if his actions were to be considered as a norm of natural behaviour, then / should have been considered an anchorite by comparison. / should be the last person in the world to condemn a little fun. provided it did not interfere with the more serious business of life. A nation can only prosper on condition o that its citizens work hard and live soberly. Of course. if Jim is bent on picking quarrels with his best friends, he may do so, provided that he does not come running to them afterwards to make friends again. If he sows his wild oats, we are not going to reap the crop.
2. I must visit Mrs. X. today, because she is not well again. If she were more careful of her health, she would not have theseattacks. Things would be different with her, if only she took the rest that she so badly needs. But she will not, unless somebody convinces her of the necessity for it. She would get into a state of nervous excitement, if her relatives were to press her too much about it. Supposing someone did so, it would only aggregate the already dangerous state in which she now finds herself. I dare say she could easily get better, provided she took a little more nourishment. But even supposing she did, it would probably be of little use, for she would immediately start overtaxing her strength again. She would work from dawn to dusk, provided she could stand on her feet. She tries to be patient, but finds it difficult. She says that if only people would remember how miserable cantankerousness makes those around them, sick people might be more patient. If she let her daughter Mary look after household matters, it would be a help. But she says that Mary is very young yet; and that the servants would probably not obey her. if she were in charge. I think that Mrs. X. is mistaken. I am sure that the servants would