I like the learning English section of the BBC web pages so much. Please, can you explain the use of the verb to be + to in these examples:
- You are not to smoke
- They are to be married soon
We use be to + infinitive when discussing formal or official arrangements or to give formal instructions or orders and your examples illustrate these aspects very well. Further examples might be:
- The Prime Minister is to make a further visit to Devon next week.
- We are to receive a pay rise in line with inflation in September.
- I don't mind her going to Ruth's party but she's not to be back late.
- You are not to leave this house without my permission. Is that clear?
The be to + infinitive structure is also frequently used in newspaper, radio and television reports to refer to future events. It expresses near certainty that what is forecast will happen. Study the following:
- A man is to appear in court later this morning charged with the murder of the footballer, Darren Gough.
- The Ministry of Trade and Industry has announced that it is to move three thousand jobs out of the capital and re-locate them in the North East.
- Work is to begin this week on the new bridge across the Nile north of Aswan.
We often use be to + infinitive in the if-clause in conditional sentences when talking about preconditions for something to happen. Study the following:
- If we are to catch that train, we shall have to leave now.
- If I were to increase my offer from five hundred to five hundred and fifty pounds, would you be interested in selling me your car then?
- If we are to solve the world's pollution problems, we must address environmental issues now.
Be to + passive infinitive is often used when giving instructions. It is noticeable always on medicine bottles and can be seen on other official notices too:
- To be taken three times a day after meals.
- These benches are not to be removed from the changing rooms.
- No food of any kind is to be taken into the examination room.
Note that although this structure is used to talk about current and future arrangements and events, it is configurated in present and past tenses - see the above examples. However, be to + perfect infinitive is sometimes used to show that a planned event did not materialise:
- He was to have appeared in the West End show but broke his collar bone during rehearsals.
- They were to have picked strawberries this morning, but the torrential overnight rain made the field too muddy.
- Sammy was to have married Sarah but then Jamie came along and the engagement ring he had given her was returned.