Modal Auxiliaries

      
I. INTRODUCTION
The modal auxiliaries in English are: can, could, had better, may, might, must, ought to, shall, should, will and would. 
Modal auxiliaries generally express a speaker's attitude's, or 'moods'. For example, modal can express that a speaker feels something is necessary, advisable, permissible, possible or probable; and in addition, they can convey the strength of these attitudes.
Each modal has more than one meaning or use.
Here are the rules for modals:
1. Modal do not take take a final -s, even when the subject is he, she or it.
He can do it   (correct)
He cans do it  (incorrect)
2. Modals are followed immediately by the simple form of verb.
He can do it  (correct)
He can to do it/ He can does it / He can did it (incorrect)
3. The only exception is ought, which is followed by infinitive (to+the simple form of verb)  
She ought to go to the meeting (correct)

Similar expressions for modal
This is a list of some common expressions whose meanings are similar to those of some of the modal auxiliaries.
be able to   
be going to
be supposed to
be to
have to
have got to
used to
For example: be able to is similar to can; be going to is similar to will.
An infinitive (to + the simple form of a verb ) is used in these similar expressions.

II. POLITE REQUESTS WITH 'I' AS THE SUBJECT
a. May I (please) borrow your pencil?
    May I and Could I are used to request permission. They are equally polite.
b. Can I borrow your pencil?
Can I is used informally to request permission, especially if the speaker is talking to someone she/he knows fairly well. Can I is usually not considered as polite as may I or could I.

III. POLITE REQUESTS WITH 'YOU' AS THE SUBJECT
a. Would you pass the salt (please)?
b. Will you (please) pass the salt?
The meaning of would you and will you in a polite request is the same. Would you is more common and is often considered more polite. The degree of politeness, however, is often determined by the speaker's tone of voice.
c. Could you pass the salt?
Basically, could you and would you have the same meaning. The different is slight:
Would you = do you want to do this please?
Could you = do you want to do this please, and is it possible for you to do this?
Could you and would you are equally polite.

d. Can you pass the salt?
Can you is often used informally. It usually sounds less polite than could you or would you.

IV. POLITE REQUESTS WITH 'WOULD YOU MIND'
Asking Permission
a. Would you mind if I closed the window?
(Please notice! Would you mind if I is followed by the simple past.)
Means: May I close the window? Is it all right if I close the window? Will it cause you any trouble or discomfort if I close the window?
But, sometimes, in informal spoken English, the simple present is used: Would you mind if I close the window?

Asking someone else to do something
b. Would you mind closing the window?
(Please notice! Would you mind is followed by -ing ( a gerund )
Means: I don't want to cause you any trouble, but would you please close the window? Would that cause you any inconvenience?

V. EXPRESSING NECESSITY (MUST, HAVE TO, HAVE GOT TO)
a. All applicants must take an entrance exam
b. All applicants have to take an entrance exam
( Must and have to both express necessity. It is necessary for every applicant to take an entrance exam. There is no other choice. The exam is required )
In everyday statements of necessity, have to is used more commonly than must. Must is usually stronger than have to and can indicate urgency or stress importance. For example:
c. Where is Sue? I must talk to her right away. I have an urgent message for her. 

d. I have got to go now. I have a class in ten minutes.
e. I have to go now. I have a class in ten minutes.
Sentence d and e have the same meaning. Have got to is informal and used primarily in spoken English. Have to is used in both formal and informal English.

Note: The idea of past necessity is expressed by had to. There is no other past form for must ( when it means necessity) or have got to. Example:
I have to/ have got to / must study tonight. (present/future)
I had to study last night (past)

VI. ADVISABILITY: SHOULD, OUGHT TO, HAD BETTER
a. You should study harder  ( This is a good idea. This is my advise)
b.You ought to study harder  ( This is an important responsibility)

Should and ought to have the same meaning: they express advisability. The meaning ranges in strength from a suggestion ("This is a good idea") to a statement about responsibility or duty ("This is very important to do ").

c. The gas tank is almost empty. We had better stop at the next service station.
In meaning, had better is close to should/ought to, but had better is usually stronger. Often, had better implies a warning or a threat of possible bad consequences. In the sentence above: If we don't stop at service station, there will be a bad result. We will run out of gas.

VII. THE PAST FORM OF SHOULD
a. I had a test this morning. I didn't do well on the test because I didn't study for it last night. I should have studied last night. 
Past form: should have+past participle
In a: "I should have studied" means that studying was a good idea, but I didn't do it. I made a mistake
b. I hurt my back. I should not have carried that heavy box up two flights of stairs. ( I carried the box and now I am sorry).
In b: "I should not have carried ", means that I carried something, but it turned out to be a bad idea. I made a mistake.
Note: The past form of ought to is ought to have + past participle.
I ought to have studied, it has same meaning as the past form of should. In the past, should is used more commonly than ought to. Had better is only rarely used in a past form (e.g. He had better have taken care of it ) and usually only in speaking, not writing.

VIII. EXPECTATIONS: BE SUPPOSED TO AND BE TO
a. The game is supposed to begin at 10:00
b. The game is to begin at 10:00
Be supposed to and be to ( a form of  be followed immediately by infinitive, e.g., is to begin ) express the idea that someone ( I, we, they, the teacher, lots of people, my father, etc ) expects something to happen. Be supposed to and be to often express expectation about scheduled events or correct procedures. In a and b: The speaker expects the game to begin at 10:00 because that is the schedule. Be to is stronger, more definite, than be supposed to.

IX. DEGREES OF CERTAINTY
"Degree of certainty" refers to how sure we are- what we think the chances are- that something is true. If we are sure something is true in the present, we don't need to use a modal. For example, if we say, "Anna is sick",  I am sure, I am starting a fact that I am sure is true. My degree of certainty is 100%.

Present time:
Why isn't Anna in class?
100% ------> She is sick
95%--------> She must be sick
Less than 50%-----> She may be sick
                                 She might be sick
                                 She could be sick

Past time:
Why wasn't Anna in class?
100% -------> She was sick
95% ---------> She must have been sick
Less than 50%------> She may have been sick
                                   She might have been sick
                                   She could have been sick

Future time:
100% ----------> Anna will do on the test well
95% -----------> Anna should do well on the test
                            Anna ought to do well on the test
Less than 50%---> Anna may do well on the test
                              Anna might do well on the test
                              Anna could do well on the test
Note: Should/ought to can be used to express expectations about future events.
In sentence: Anna should/ought to do well on the test tomorrow, I expect her to do well. That is what I think will happen.

X. PROGRESSIVE FORM OF MODAL
Progressive form,present time: modal +be+ -ing
Meaning: in progress right now
Example:
Let's just knock at the door slightly. Tom may be sleeping. (right now)
Progressive form, past time: modal + have been + -ing
Meaning: in progress at a time in the past.
Example:
Suzan wasn't at home last night when we went to visit her. She must be have been going to the market.

XI. USING WOULD TO TO EXPRESS A REPEATED ACTION IN THE PAST



a. When I was a child, my mother would read me a story before going to bed.
b. When I was a child, my mother used to read me a story before going to bed.
Would can be used toexpress an action that was repeated regularly in the past. When would is used to express this idea, it has same meaning as used to (habitual past)

XII. USING USED TO TO EXPRESS HABITUAL PAST AND BE USED TO
a. Jenny used to lived in Bangkok
Meaning : At a time in the past, Jenny lived in Bangkok, but he does not live in Bangkok now. Used to to expresses a habit, activity or situation that existed in the past but which no longer exists.

b.Sam is used to cold weather.
c. Sam is accustomed to cold weather.
Meaning : Be used to means be accustomed to.
In b and c have the same meaning: living in cold weather is usual and normal to Sam. Cold weather, snow and ice do not seem strange to Sam.

d. Sam moved to Canada. After a while she got used to / got accustomed to living in a cold climate.
In the expressions get used to and get accustomed to, get means become.

Now compare 2 sentences below:
e. Lateefa used to live in Indonesia.
f. Sam is used to living in a cold climate. She is accustomed to living there.
To express habitual past, used is followed by an infinitive, e.g., to live as in sentence e.
Be used to and be accustomed to are followed by an -ing verb form ( a gerund ), e.g., to living as in sentence f.


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