What are the different meanings of "to be to"? Just the ones that spring to my mind, Cyril.
obligation: I am to go by bus as my car is broken. arrangement (in advance) : A agreed I am to tell him tomorrow. future : The patient was to die by the end of the night.
"be to" followed by infinitive.
* About something that is LIKELY TO HAPPEN soon (what AhQ put as future): Due to the floods many homes are to collapse. With fires extension, some more Russians are to die. After last racketeerings cops are to search passers-by. By this time of vacations you'll be to wait a lot before managing to cross the St-Gothard. If you study a bit, you are to pass the exam.
* About a FUTURE FROM THE PAST The nurses took care of the patient but he was to die by the end of the night. (AhQ quoted) The patient was to recover due to a shock treatment. He was to win the medal as no one could challenge him. She was to get her husband under her thumb, so a paltry man he was.
* About FUTURE EVENTS THAT CAN BE CONTROLLED BY PEOPLE Obama is to make a speech tomorrow. (or: will make) Nobody know when the disease will appear again (not: 'is to appear' as the disease reappearance can't be controlled.)
* About FORMAL ARRANGEMENTS, OBLIGATIONS, ORDERS ... As agreed I am to tell him the truth. To abide by my wife's last wishes I am to die tonight. According to the law I am not to kill my neighbour. Dogs are not to run in the park unless kept on the leash.
* In IF-CLAUSES As something is to happen first before something else (in the if-clause): If I am to speak English fluently next week, I need to study today. If Jack is to win the race, he has to start quickly.
(Done with the help of a grammar. Is to be checked anyway. CW)
NB CW for 'corrections welcome'
A simple thing to help remember: insert the word 'expected' or 'allowed' between the 'be' verb (no matter what tense) and 'to', for example, 'to be (expected) to' or 'to be allowed to". If you go back through all the sentences Joe posted and insert the word 'expected' or 'allowed' (as context dictates), you'll see they make more sense.
The nurses took care of the patient but he was (expected) to die by the end of the night. Obama is (expected) to make a speech tomorrow. As agreed, I am (expected) to tell the truth. According to the law I am not (allowed) to kill my neighbour. Dogs are not (allowed) to run in the park.
Thank you, Kiera the Sixth, for confiding that trick. Pretty handy!