The Grammaring Guide to English Grammar with Exercises

BE + TO-infinitive

Be + to-infinitive is used to express:

official arrangements: The Prime Minister is to visit India next month.

official orders: At the end of the course, all students are to take a written exam.

things that should be done: What am I to do?

a possible aim when saying what should be done to reach it: If you are to work here for more than three months, you must have a residence permit.

prohibition (only in the negative): You are not to do that again.

Be + to-infinitive can also be used in the past:

Mr Jones

was to speak

at the meeting.

(it was arranged and he did)

But was/were + to + perfect infinitive means that the arranged event did not actually happen:

Mr Jones

was to have spoken

at the meeting, but he had to cancel because of his illness.

Quotes:

Nothing in life is to be feared. It is only to be understood. - Marie Curie