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1) SHOULD
- OUGHT TO
Should and ought to are interchangeable for advice and
conclusions :
♦ You should / you ought to write to your grandmother.
♦ He has revised all day; he should / he ought to be ready for his
exam.
Should is also used :
◊ In hypothetical situations :
♦ Should anyone call, please take a message.
♦ Should you need any help, just call me.
♦ If I were you, I should leave. (In this last example, 'would'
is often used today.)
◊ With imagine, say, think to give tentative opinions
:
♦ I should think the journey will take about two hours.
2) NEED
Need expresses necessity.
♦ In summer, we need to drink more often. (= it is necessary for us
to drink water)
♦ You needn't / you don't need to take notes. You'll get a
summary.
(= it isn't necessary to take notes)
♦ Need I / Do I need to do this? (= is it necessary for me to do
this?)
3) NEEDN'T HAVE - DIDN'T NEED TO
◊
Needn't have is used to refer to an action which
was performed
but later turned out to be unnecessary.
♦ We needn't have rushed to the airport; the flight was delayed.
♦ He needn't have taken a sweater; the weather was warm.
◊ Didn't need to is used to refer to an action in
the past which was not performed
because there was no need for it.
♦ We didn't need to show our passports - ID cards were accepted.
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