Modal Verbs (Expressing Necessity. Expressing lack of necessity. Expressing future, present or past ability)

    Expressing  Necessity

(a) Must means that something is very necessary; there is no other choice. It is a “strong” word

(b) Have to has basically the same meaning that something is necessary. 

(c) Has got to is generally used only in informal speech and writing and usually pronounced like “gotta”

(d)  The past form of must and have to is had to.

Expressing  lack  of Necessity

The idea that something is not necessary is expressed with {don’t/doesn’t} have to (1) or with needn’t (2):

1. Tomorrow is a holiday. Mary doesn’t have to go to class.

2. You needn’t learn this poem.

Expressing future, present or past ability

(a) We use can (and sometimes am/ is/ are able to) to describe natural (1) or learned (2) ability:

1. I can (I am able to) run 1500 metres in 5 minutes. 2. I can’t (I am not able to/ I am unable to) drive.

(b) We use could, couldn’t or was/ were (not) able to to describe “general ability in the past”:

I could (I was able to) run very fast when I was a boy.

(c) We use was/ were (not) able to or managed to (not could) to describe the successful completion of a specific action: We were able to (we managed to) get tickets for the match yesterday. (Not could)

(d) However, we can use couldn’t to describe a specific action not successfully completed:

We couldn’t get tickets for the match yesterday.

Or: We were not able to (we didn’t manage to) get tickets for the match yesterday.

(e) Can and could are not “complete verbs” so we use be able to and sometimes managed to if, for example, we want to express the future or the present perfect:

I’ll be able to pass my driving test after I have had a few lessons. Not “I can/ I will can”

Can/ could with verbs of perception

We do not use progressive with verbs of perception (see, hear, smell, etc.) when we are describing something that is happening now: I see a bird in that tree.

(a) We often use can + verb in place of the simple present with verbs of perception:

I can see a bird in that tree. (= I see...) Can you see it? (= Do you see…)

(b) We often use could + verb in place of the simple past with verbs of perception:

I looked up, but couldn’t see anything. (= didn’t see…)

Uses of modals (etc.) to express permission and prohibition

1. We use can, could, may, might to ask for permission, depending on the situation

(a) Can is the commonest and most informal: Can I borrow your umbrella (please)?

(b) Could is more polite than can: Could I borrow your umbrella (please)?

(c) May is more respectful than can and could: May I borrow your umbrella (please)?

(d) Might is the most polite but the least common: Might I borrow your umbrella (please)?

2.  We personally give or refuse permission in everyday situations in the following way:

(a) You {can (not)/may (not)}watch TV for as long as you like. (Not could or might)

(b) We refer to “some other authority” that gives/ refuses to give permission like this:

You     can (cannot)/ are allowed to (not allowed to)/ are permitted to (not permitted to)            smoke here.

mustn’t/ are forbidden to

(c)    May and must are not “complete verbs” so we use to be allowed to tomake up their missing parts in tenses other than present and future: The children were allowed to watch TV last night. (Not could)

Can (=ability) and can/could (=have permission, be free to)

(a) We use can/could in the sense of “am/is/are free to” to refer to the future:

Mr. Jones can/could see you tomorrow, if you are free. Or Mr. Jones is able to see you…

(b) But we must use will be able to (not can/could) to describe future ability:

Baby will be able to stand up in two weeks’ time. (not can/could)

                                            Certainty and possibility for the past and present

If we are referring to possibility, we use may, might, can or could + verb:

(a) To be: Jane may/might/can/could be at home now. Jane may/might/can/could have been at home yesterday.

(b) Any full verb: For the present  Jane may/might/can/could work (or… be working) at home now.                   

For the past    Jane may/might/can/could have worked (or… have been working) at home yesterday.

Deduction

We express deduction with must have Ven, can’t/couldn’t have+Ven  (for the past) or must+verb/can’t+verb

He must be at home. He can’t be out. (now)               He must have been at home yesterday.

He must live abroad. (now)          He must have lived abroad (before)