Page 112 - Practical English Usage 3ed - Michael Swan, Oxford

90
Who's being a silly baby, then?
- I'm happy just now. (NOT tnt being httppyjf:tSt 1l8W.)
I was depressed when you phoned. (NOT ,r WtfS being depressed . ..)
Note the difference between He's being sick (BrE = He's vomiting - bringing food up from the stomach) and He's sick (= He's ill).
For the use of am being etc in passive verb forms. see 412.2.
be with auxiliary do
Normally, be is used without the auxiliary do. I'm not often sick. (NOT 1 tltm't qften be sick)
But do is used to make negative imperative sentences with be (when we tell somebody not to do something).
Don't be silly! Don't be such a nuisance! And do be can begin emphatic imperatives.
Do be careful! Do be quiet, for God's sake!
In an informal style, people sometimes use do with be in one or two other structures which have a similar meaning to imperative sentences.
Why don't you be a good boy and sit down? Ifyou don't be quiet you'll go straight to bed.
For other auxiliary uses of do. see 159.
be + infinitive: I am to ..., you are to ... etc plans and arrangements: He is to visit Nigeria
We use this structure in a formal style to talk about official and other plans and arrangements.
The President is to visit Nigeria next month.
We are to get a 10 per cent wage rise in June.
I felt nervous because I was soon to leave home for the first time.
A perfect infinitive can be used to show that a planned event did not happen.
I was to have started work last week, but I changed my mind. 'fate': We were to meet again
Another use is to talk about things which are/were 'hidden in the future', fated to happen.
I thought we were saying goodbye for ever. But we were to meet again. many years later, under very strange circumstances.
pre-conditions: If we are to get there in time ...
The structure is common in if-clauses, when the main clause expresses a pre-condition - something that must happen first if something else is to happen.
Ifwe are to get there by lunchtime we had better hurry.
He knew he would have to work hard ifhe was to pass his exam.
91 1
2
3
be with auxiliary do 90
page 80