Modal Auxiliaries

In English there are 11 modal auxiliaries.

Can, Could, Had better, May, Might, Must, Ought to, Shall, Should, Will, Would.

Modal auxiliaries generally express a speaker’s attitude or ‘moods’. For example, modals can express that speaker feels something is necessary, advisable, permissible, possible, or probable; and in addition, they can convey the strength of these attitudes.

Source: Betty Schrampfer Azar, UNDERSTANDING AND USING ENGLISH GRAMMAR SECOND EDITION

Polite Request (Permission) with ‘I’ as the subject

a.       May I borrow your phone? b.       Could I borrow your phone? c.       Might I borrow your phone?	a.       ‘May’ used when we don’t know what the answer is. b.       ‘Could’ is almost same with ‘May’ but in this case, we are sure that we will get permission. c.       ‘Might’ is quite formal and it used much less frequently than ‘May’ and ‘Could’
d.      Can I borrow your phone?	d.      ‘Can’ is used informally. It’s usually not considered as polite as ‘May’ or ‘Could’.
Typical Responses Formal: Yes, certainly. Of course. Yes, of course. Informal: Sure.	Often the response to a polite request consists of an action, a nod or shake of the head, or only saying “uh-huh.”

Polite Request (Permission) with ‘U’ as the subject

Would you explain it? Will you explain it?	‘Would’ is more common and is often considered more polite than ‘Will’. However, is often determined by the speaker’s tone of voice.
Could you explain it?	‘Could’ in this case, is almost same with Could with sb I. it is possible for you to do it
Can you explain it?	‘Can’ is used to informal.
Typical responses Formal: Yes, I’d (I would) be happy to. Yes, I’d be glad to. Certainly. Informal: Sure.	If a negative response is necessary, a person might begin by saying, “I’d like to, but …..” (e.g., I’d like to explain it, but I am in hurry.”

Polite Requeast with ‘Would you mind’

Asking Permission
a.       Would you mind if I opened the door? b.       Would you mind if I used the book?	Would you mind if I is followed by the simple past. However it doesn’t refer to past time, it refers to present or future time. *sometimes in informal spoken English, it is ok if the simple present is used (e.g., Would you mind if I open the door?” It means: May I open the door? Is it all right if I open the door? Will it cause you any trouble or discomfort if I open the door?
Typical Responses No, not at all. No, of course not. No, that would be fine. *it doesn’t mean its negative response.

Asking someone else to do something
c.       Would you mind opening the door? d.      Excuse me? Would you mind repeating that?	Would you mind is followed by –ing (a gerund). It means: I don’t want to cause you any trouble, but would you please open the door? Would that cause you any inconvenience?
Typical Responses No, I’d be happy to. Not at all. I’d be glad to.

Using Imperative Sentence to Make Polite Request

a.       Shut the door. b.       Be on time. c.       Don’t shut the door. d.      Don’t be late.	Imperative sentence has an understood subject (you), and the verb is the simple form. In the negative, don’t precedes the simple form of the verb.
e.       Turn left at the corner. f.       Please shut the door. g.      Shut the door, please. h.       Shut the door, could you? i.         Have a seat, won’t you?	Imperative sentence can be used to give an order, or direction. In polite request, word please is added. Would you/could you is added as a tag question. In formal situation, won’t you is added as tag question.

Requirement expression: must, have to, have got to.

a.       All vehicles must contain gasoline. b.       All vehicles have to contain gasoline.	In this case, must and have to for expressing necessary. It because it is necessary for every vehicles to contain the gasoline. There is no other choice. The gasoline is required.
c.       I have to go to toilet. d.      I must go to office now.	Have to is used more commonly than must. Must indicate urgency or stress important and it is stronger than have to.
e.       I have got to go now. f.       She has to go now.	Have got to and have to have the same meaning. Have got to is used to in spoken English and it’s informal. Have to is used to formal and informal.
Present or future: g.      I have to go tonight. h.       I have got to go tonight. i.         I must go tonight.	Past: j.       I had to go last night
In spoken (informal) Have to is usually pronounced “hafta” and Has to “hasta”. Have got to can pronounced “have gotta” and sometimes have is dropped in speech becomes “gotta” only.	Have to + V1 Has to Have got to Has got to Must Had to

Have to and must in negative form.

Lack of necessary a.       I don’t have to go to office in weekend. b.       I can hear you. You don’t have to shout.	Must and have to have different meaning when it used in negative form. Don’t have to has meaning ‘need not’.
Prohibition c.       You must not look in the closet. d.      You must not tell anyone my secret.	Must not = don’t do this. Mustn’t used to pronounced “muss-әnt”.

Should > Ought to > Had better

a.       You should try again. b.       You ought to try again. (rare) c.       You shouldn’t leave your phone. d.      You oughtn’t (to) leave your phone.	Should and ought to are for express advisability. Its strength from a suggestion about responsibility or duty. Ought to in negative form used to be oughtn’t and the to is often dropped.
e.       We had better go first. f.       You’d better take care of it. g.      You better take care of it. (speaking) h.       You’d better not be late.	Had better is usually stronger than should or ought to. Often had better a warning or a threat of possible bad consequences. Had better is followed by the simple form. (Present or future meaning) it’s more common in speaking.

Should in past tense

a.       I should have worked last night. b.       You should have given it to me.	Should have + past participle (V3) Should have is used to pronounced “should-of” or “shoulda”.
c.       I should not have pushed you. d.      You should not have gone to park.	Should not have is used to pronounced “shouldn’t-of” or “shouldn’t’a”.
Informal, rarely used in past form, and usually only in speaking.	Ought to > ought to have + past participle. Had better > had better have + past participle.

Expectation: be supposed to and be to

a.       She is supposed to take off at ten. b.       She is to take off at ten. c.       She is supposed to come tomorrow. d.      She is to come tomorrow.	Be supposed to and be to are followed by an intinitive (to + V1). Both are express expectations about scheduled event or correct procedures. Be to is stronger and more definite than be supposed to.
Compare: e.       I should go the meeting. I can get some information if I go. Going to the meeting is a good idea. f.       I am supposed to go to the meeting. My boss told me that he wants me to attend.	Be supposed to and be to express expectations about behavior. (give the idea to do something). The difference be supposed to with should: be supposed to gives the idea that someone else expects (require or request) the behavior.
Compare: g.      I must be at the meeting. The meeting can’t occur without me because I’m the only who has certain information. h.       I am to be at the meeting. My boss ordered me to be there. He will accept no excuses.	The difference be to with must: be to includes the idea that someone else strongly expects (demands or order) the behavior. Be to is used to state strong expectations: e.g., rules, laws, instructions, demand, orders.

*to be continue :)