22. Means of expressing permission, emphatic advice, prohibition, obligation

22. Means of expressing permission, emphatic advice, prohibition, obligation

FUNCTION	VERB	INFINITIVE	USAGE	EXAMPLES
permission	can	simple		You can go to the party.
could	simple	in reported speech due to sequence of tenses	He said she could take his car, but asked her to return it as soon as possible.
may	simple		You may take this.
might	simple	used in the reported speech	He said I might take this.
emphatic advice	must	simple	+ / --	He must find this information himself. Then he’ll remember it better.
prohibition
must	simple	--	You mustn’t turn the radio on so loudly.
may	simple		You may not take this.
might	simple	strict prohibition	No, you might not.
can	simple		You can’t go to the party.
could	simple		He said she could take his car.
obligation	shall (compulsion, strict order)		2^nd and 3^rdpersons	What a mess! You shall do up now!
should (advisability, desirability)	+ / -- /?	simple	reference to the future	We should discuss the matter over.
simple / continuous	reference to the present (stative / durative verbs)	You should be doing up accurately.
+	perfect	desirable action wasn’t fulfilled	You should have accepted the offer.
--	perfect	undesirable action was fulfilled	You shouldn’t have bought this awful sofa.
have to (imposed by the circumstances)	simple	+ /?	We have to hurry up a bit.
be to (due to the arrangement)	+ /?	simple	present or past actions	I am to be there at 10.
perfect	unfulfilled plan	He was to have been there at 10.
ought to (advisability, desirability)	+ / -- /?	simple	reference to the future	You ought to visit granny.
simple / continuous	reference to the present (stative / durative verbs)	You ought to be studying hard.
+	perfect	desirable action wasn’t fulfilled	You ought to have kept this secret to yourself.
--	perfect	undesirable action was fulfilled	You oughtn’t to have shouted at your mother.
must (from the speaker’s point of view)	+ /?	simple	duty, necessity	You must study hard to get a good job.

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