Be to+infinitive is used:
1) – to talk about formal or official arrangements, formal instructions, and to give orders. It is particularly common in news reports to talk about future events.
Example: You are not to leave the school without my permission.
We only use to be+infinitive to talk about things that can be controlled by people:
Example: We don’t know where the meteorite is going to land. (not ... the meteorite is to land.) I suppose we will all die eventually. (not... we are all to die.)
2) – in if-clauses to say that something must take place first (in the main clause) before something else can take place (in the if-clause):
Example: If humans are to survive as a species, we must address environmental issues now.Compare: a) Jones needs to improve his technique if he is to win gold at the next Olympics. b) Jones has said that he will retire from athletics if he wins gold at the next Olympics.
Ex. 1
Complete these sentences on the news. Some are spoken by the newsreader in the studio and some by reporters on the spot. Use to be or to be about with the verbs in brackets.
1. The new museum _______ (open) in the autumn. 2. The Prime Minister is at the microphone now. He ________ (start) speaking. 3. The leading runner is nearly there now. She _______ (win) the race. 4. Taxes ______ (go) up from next April. 5. The US President _______ (visit) Ireland in the new year. 6. The riot isn’t over yet, but the police are here. They _____ (move) in. 7. The talks on world trade ________ (take) place later this year.
Ex.
Ex. 2
Use to be + Infinitive if possible, and will if not: