12 MODALS AND RELATED VERBS 2 55
To talk about permission in the past, we use could, was allowed to.
In my last job I could/was allowed to use the phone for personal calls.
To talk about prohibition in the past, we use couldn't, wasn't allowed to.
In my last job I couldn't/wasn't allowed to use the phone for personal calls.
D Opinions and advice
I We use should, should not {shouldn't), ought to and ought not to (oughtn't to) to give an opinion or recommendation about what is the best thing to do. We should/ought to invest more heavily in marketing.
By midnight Kennedy had 265 electoral votes, just jour short of victory. Nixon wasn't ready to concede, but he thought he should make some kind of statement to his supporters in the ballroom downstairs. Kennedy watched this on TV 'Wliy should he concede?' Kennedy said to his aides. 'I wouldn't.' (Washington Post website)
When we use you speaking to someone else our opinion becomes advice. You should speak to your boss, (it's my advice to you)
Note that advice is like a weak type of necessity (section A).
You should/ought to go to the doctor, (advice: it's the best thing to do)
You must/have to go to the doctor.     (strong advice: it's really necessary)
had better (not) is used for strong opinions. Had is usually contracted. I'd better not interrupt him while he's on the phone. I think you'd better call them straightaway.
E Past criticism
When we use the verbs in section D in the past (+ have + past participle) we mean that we
didn't do the right thing and now we are making a criticism.
We should have seen the dangers a long time ago.
We shouldn't have spent all the advertising budget on television spots.
You ought to have mentioned that earlier.
F Need to
Need to means the same as have to (sections A/B).
You have to Ineed to sign this form in two places, here and here.
If you're going to jump into the UK market and become an important player, you need to have wine that retails in the £,6-£7 price range. (NewYork Times website)
Notice the two possible negative forms.
You don't need to/needn't wait for me - /'// come along later.
In strict grammar the two negative forms have different meanings in the past.
/ didn't need to arrive at seven, (we don't know when I arrived - maybe seven or later)
/ needn't have arrived at seven, (we know when I arrived - seven - but it wasn't necessary)
But in everyday speech we often use didn't need to for both cases.