3. Formation of tenses with Modal Verbs
Modal verbs do not have the future tense form. The future is expressed by the present tense forms of modal verbs with the help of the context and adverbs of time referring to the future. (With the exception of the modal verbs WILL, WOULD, of course, which express the future.)
Can I go there tomorrow? – Yes, you can.
Can they go there now? – No, they can't.
He shouldn't call her today.
They should call her tomorrow.
Only two modal verbs can form the past by changing their forms directly. They are CAN, COULD and WILL, WOULD (only in some of their meanings).
She can sing very well. – She could sing very well when she was younger.
He will go there tomorrow. – I said that he would go there tomorrow.
The pair SHALL, SHOULD with the future meaning can still work like that in British English. In American English, WILL is used for all persons in the future (WOULD for the Future in the Past), and SHALL, SHOULD are used mostly as separate modal verbs.
Shall we wait for you here? (polite suggestion of some action and asking for consent or directive)
Should we call her? (asking for advice; present or future)
You should have called her yesterday. (giving advice; past tense)
The verbs MAY and MIGHT are used mostly as separate modal verbs, though MIGHT is generally used instead of MAY in cases where the rules of the sequence of tenses require the use of the past tense form of the verb.
She may be at the hospital now. – I said that she might be at the hospital now.
4. Meanings of modal verbs
The meanings of modal verbs are extremely important for understanding how modal verbs work. This or that modal verb in one of its meanings can't form the past tense; in another meaning it is used only with a negative; in still another meaning it can't form a question or, on the contrary, is used only in the form of a question.
The meanings of modal verbs are created by the context and by the grammatical structures in which they are used. If the context is not clear enough, it may be difficult to understand in which meaning a modal verb is used. For example, look at this sentence: "You must speak English." Does it mean "You have to speak English" or "You probably speak English"? We need more context to say for sure, for example, "You must speak English at the conference" (strong necessity) or "You have lived in Canada for several years, you must speak English" (strong probability).
Certain grammatical structures also provide additional context and help us choose the right meaning of a modal verb. For example, quite often the use of the infinitive BE after certain modal verbs is an indication that the meaning is "probability, possibility".
He must be rich.
They may be at home.
She could be sleeping now.
The meanings of modal verbs are a little difficult to single out and define clearly (especially if we try to define them in Russian). For example, when speaking about the main meaning of the verb CAN, some linguists use the words "ability, possibility", others speak about "physical and mental ability", still others say "ability, power, skill, opportunity". The material Overview of Modal Verbs describes the meanings of modal verbs in general, and typical examples of use are given. The materials on specific modal verbs describe their meanings, usage, and peculiarities in detail. Specific modal verbs are grouped by their meaning in the materials of this section, e.g., Ability, Advice, Necessity.
Will/ Shall (would/should)
We use will when we decide to do something at the time of speaking:
Oh, I’ve left the door open. I’ll go and shut it.
‘Did you phone Lucy?’ ‘Oh no, I forgot. I’ll phone her tomorrow.’
We use will in the following situations:
Offering to do something
That bag looks heavy. I’ll help you with it.
Agreeing to do something
A: Can you give Tim this book?
B: Sure, I’ll give it to him when I see him this afternoon.
Promising to do something
‘Can you give me the money? I’ll pay you back on Friday.’
Asking somebody to do something
Will you please turn the radio down? I’m trying to concentrate.
Shall is used mostly in the questions shall I …? / shall we…? to ask somebody’s opinion (especially in offers and suggestions):
Shall I open the window?
Shall we go now?
We use would/wouldn’t when we imagine a situation or action (we think of something that is not real):
It would be nice to buy a new car, but we can’t afford it.
I’d love to live by the sea.
Should is used to give an advice or to give an opinion:
‘You look tired. You should go to bed.’
The government should do more to reduce crime.
Should is not as strong as have to and must.
Can/Could/be able to
We use can to say that something is possible or allowed, or that somebody has an ability to do something. We use can + infinitive (can do, can see etc.)
We can see the lake from our bedroom window.
Can you speak any foreign languages?
The word ‘play’ can be a noun or a verb.
The negative form of can is cannot or can’t
Can has only two forms: can (present) and could (past). So sometimes it is necessary to use be able to.
e.g. a) Maria can speak French, Spanish and English.
b)Applicants for the job must be able to speak two languages.
May/Might
We use the modal verbs "may" and "might" to talk about possible activities or happenings in the future:
e.g. I'm not sure I'll go to the party. I may be away.
Don't drop by at 7:20 PM. I might be watching TV.
Please, prepare something to eat. Mr. Johnson might be hungry.
We may not be able to go to school this week.
There isn't much difference between the two. So you can say:
"John might be at home" or "John may be at home".
"I may visit Mary" or "I might visit Mary".
Sentences formed with "might" are less likely to happen than those with "may". For example:
I may be away at 10 PM. (35% likelihood)
I might be away at 10 PM. (20% likelihood)
Of course, these figures may vary depending on the situation.
However, when the situation is unreal, only "might" can be used:
If I were a bit smarter, I might go to college. (The speaker won't become smarter, so the situation is unreal)
If you want to emphasize progression of a situation, you may use the continuous form of the verb after the modal.
Don't drop by at 7:20 PM. I may/might be watching TV.
Need (necessity)
The modal verb need may be either a defective or a regular verb. As a defective verb need has only one form and combines with a bare infinitive. In reported speech it remains unchanged. As a regular verb it has the past indefinite form needed and regular negative and interrogative forms.
The defective form is mainly restricted to negative and interrogative sentences, whereas the regular verb can be used in all types of sentences and is therefore more common.
e.g. You needn’t do it just now.
The teacher said that we needn’t come.
Have to (obligation)
Have to is often grouped with modal auxiliary verbs for convenience, but in fact it is not a modal verb. It is not even an auxiliary verb. In the have to structure, "have" is a main verb. The structure is: subject + auxiliary verb + have + infinitive (with to)
In general, have to expresses impersonal obligation. The subject of have to is obliged or forced to act by a separate, external power (for example, the Law or school rules). Have to is objective. Look at these examples:
In France, you have to drive on the right.
In England, most schoolchildren have to wear a uniform.
John has to wear a tie at work.
In each of the above cases, the obligation is not the subject's opinion or idea. The obligation is imposed from outside.
We can use have to in all tenses, and also with modal auxiliaries.
Must (obligation, prohibition)
Must is a modal auxiliary verb. It is followed by a main verb. The structure is:
subject + must + main verb
In general, must expresses personal obligation. Must expresses what the speaker thinks is necessary. Must is subjective. Look at these examples:
I must stop smoking.
You must visit us soon.
He must work harder.
In each of the above cases, the "obligation" is the opinion or idea of the person speaking. In fact, it is not a real obligation. It is not imposed from outside.
We can use must to talk about the present or the future. Look at these examples:
I must go now. (present)
I must call my mother tomorrow. (future)
We cannot use must to talk about the past. We use have to to talk about the past.