The modal verb “to Be to” in English

То be to as a modal verb has two tenses: the Present and Past Indefinite. It expresses the following meanings:

• Necessity due to a plan or some kind of previous ar­rangement
  • He is to come at exactly five
  • She was to phone after dinner

NOTE: A perfect infinitive after the verb to be shows that the action had been planned but wasn’t carried out

• • He was to have come at seven and now it’s already nine (He didn’t come)
• Strict orders, formal commands or formal instruc­tions
  • You are to report to the Captain.
• Strict prohibitions
  • You are not to tell anybody about it
• Something that is destined to happen
  • It was to happen. She was to become his wife
  • If we are to be neighbours for life, we should be on friend­ly terms
• Asking for instructions
  • What are we to do?
  • Where am I to go?
• It is very close to can and may
  • Where is he to be found?
  • Nothing was to be done