The modal auxiliaries (or modals) include the following: Can, could, may, might, must, should, will, would . . . Modals are always followed by the base form of a verb or auxiliary verb. Modals are always the same form no matter what the subject is.
In standard American English, a predicate verb phrase cannot contain more than one modal. Correct He will be able to go. Not correct * He will can go. Below are examples sentences containing the modal may and the verb go. Notice that the form of the modal does not change. Also notice that the base form of a verb or auxiliary verb always follows the modal. I may go. You may go. He may go. It may go. We may go. They may go. He may have gone. They may have gone. He may be going. They may be going. He may have been going. They may have been going Modals and related verb phrases add meanings to verbs. Below are some of those meanings:
Future: will be able to Present: can, am/is/are able to Past: could, was/were able to
Present/future: can, could, will, would
Future: will be allowed to Present/future: may, can, could, am/is/are allowed to Past: could, was/were allowed to
Present/future: may, might, could Past: may have, might have, could have
Present/future: couldn’t, can’t Past: couldn’t have
Present/future: should, ought to, had better Past: should have, ought to have, had better have
Present/future: should, ought to Past: should have, ought to have
Future: will have to
Present/future: must, have to, has to Past: had to
Future: won’t have to Present/future: don’t have to, doesn’t have to Past: didn’t have to
Present/future: must not, may not, cannot Past: could not
Present: must, have to, has to Past: must have, have to have, has to have
The choice of modal depends partly on the social situation. We often use formal language with strangers (people we don’t know) and superiors (people with some power over us such as our employers, doctors, and teachers). We often use informal language with our equals (our friends and family) and subordinates (people we have some power over such as our employees or children). General requests (present and/or future): Will you help me? (Informal Are you willing?) Would you help me (Formal Are you willing?) Can you help me? (Informal Are you able?) Could you help me (Formal Are you able?)
Requests for permission (present and/or future): May I leave the room? (Formal) Might I leave the room? (Formal rarely used) Could I leave the room? (Less formal Can I leave the room? (Informal) Expressing suggestions, advice, warnings, necessity (present and/or future): The choice of modal depends partly on the urgency of the message or the authority of the speaker/writer or both. Suggestions: You could see the doctor. You might see the doctor. Advice: You should see the doctor. You ought to see the doctor. Warning/strong advice: You had better see the doctor. Strong advice/necessity: You have to see the doctor. You have got to see the doctor. You must see the doctor. No choice: You will see the doctor.
(Beliefs about present time) The choice of modal depends partly on what the speaker or writer believes. Someone is knocking at the door. That could be Fred. That might be Fred.
= It’s possible. I’m less than 50% sure. That may be Fred. = It’s possible. I’m less than 60% sure. That should be Fred. That ought to be Fred. = I’m expecting Fred and I think he’s here. That must be Fred. That has to be Fred. That has got to be Fred. = It’s probably Fred. I have a good reason to believe it is Fred. That will be Fred. = I believe it is Fred. I’m about 99% sure. That can’t be Mary. That couldn’t be Mary. = It’s impossible. I’m about 99% sure. That is Fred. = I know its Fred. I’m 100% sure. Their form They help verbs. They express a wide range of meanings: Ability, possibility, permission, necessity… Most of the Modals have more than one meaning. Can – could – may – might – should – would – had better Will – must, Have to – ought to – have got to. The simple form of the verb follows all of them. Examples: She should work harder. I have got to travel this summer.
She has to do her homework herself. Would you speak more slowly please? You had better see him after your conflict. Shouldn’t you save a little money for a rainy day? You must not wait like this! May I have this pen to write down some words? You’d better not come late!
Can expresses ability in the present or future. Can = is able to (present) = Will be able (future) The negative of can is: Can’t = cannot = can not The past form of can is could. Its negative is couldn’t = could not. Could express the ability in the past. Could = was able (past) Examples: I can buy a screwdriver at a hardware store. But I cannot use it. (Present) She could speak English, but she couldn’t write it. (Past)
May is usually used in formal situations, can is used in Informal situation. Examples: You may borrow my car when you come. Can I borrow your book?
: May I, could, Can I, Might I? : “I ” is the subject We use those modals to ask polite questions. The questions ask for Someone’s permission.
May I is more formal than could I. Please is often included In questions. Might I is less frequently used. But it has the same meaning And usage as may I and could I. Can I is sometimes used informally to request permission, Especially if the speaker is talking to someone fairly well known. Examples: Would you mind if I close the door? (Informal spoken English) Would you mind if I closed the door? (Formal) “Would you mind if I” is followed by the simple past. The meaning of the question is: May I close the door? Is it all right if I close the door? Will it cause you any trouble or discomfort if I close the door? Typical responses: No. No at all. Unh-unh = No. 4.3.2. Asking somebody else to do something Would you mind closing the door? "Would you mind if`" I is followed by a gerund. The meaning is: I don’t want to cause you any trouble, but would You please close the door? Would that cause you any inconvenience?