Page 308 - English Grammar in Use

Appendix 4

Modal verbs (can/could/will/would etc.)

This appendix is a summary of modal verbs. For more information, see Units 21–41.
4.1 Compare can/could etc. for actions:
can I can go out tonight. (= there is nothing to stop me)
I can’t go out tonight.
could I could go out tonight, but I’m not very keen.
I couldn’t go out last night. (= I wasn’t able)
can or Can ⎫ ⎬ I go out tonight? (= do you allow me?)
may May ⎭
will/won’t I think I’ll go out tonight.
I promise I won’t go out.
would I would go out tonight, but I have too much to do.
I promised I wouldn’t go out.
shall Shall I go out tonight? (= do you think it is a good idea?)
should or should
I go out tonight. (= it would be a good thing to do)
ought to ought to
must I must go out tonight. (= it is necessary)
I mustn’t go out tonight. (= it is necessary that I do not go out)
needn’t I needn’t go out tonight. (= it is not necessary)
Compare could have … / would have … etc. :
could I could have gone out last night, but I decided to stay at home.
would I would have gone out last night, but I had too much to do.
should or I should have gone out last night. I’m sorry I didn’t.
ought to ought to
needn’t I needn’t have gone out last night. (= I went out, but it was not necessary)

4.2 We use will/would/may etc. to say whether something is possible, impossible, probable, certain etc.
Compare:

will ‘What time will she be here?’ ‘She’ll be here soon.’
would She would be here now, but she’s been delayed.
should or She ⎫ should ⎫ ⎬ be here soon. (= I expect she will be here soon)
⎬
ought to ⎭ ought to ⎭
may or ⎫ may ⎫
⎪ ⎪
might or She ⎬ might ⎬ be here now. I’m not sure. (= it’s possible that she is here)
⎪ ⎪
could ⎭ could ⎭
must She must be here. I saw her come in.
can’t She can’t possibly be here. I know for certain that she’s away on holiday.
Compare would have … / should have … etc. :

will She will have arrived by now. (= before now)
would She would have arrived earlier, but she was delayed.
should or should
I wonder where she is. She have arrived by now.
ought to ought to
may or ⎫ may ⎫
⎪ ⎪
might or She ⎬ might ⎬ have arrived. I’m not sure. (= it’s possible that she has arrived)
could ⎪ ⎭ could ⎭ ⎪
must She must have arrived by now. (= I’m sure – there is no other possibility)
can’t She can’t possibly have arrived yet. It’s much too early. (= it’s impossible)
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