To-infinitive

The meaning of "to be + infinitive" and "must + base verb" is very similar. The former is more impersonal and formal and is often seen in official warnings and instructions. It would be very unusual in a one-to-one situation, where "must" would be much more common.

Kind regards, Michael

That use of the infinitive can have either meaning. Context will usually determine which is intended.

lucas21c1. Can this sentence, "You are to clean your room", be interpreted as follows?(1) You are going to clean your room.(2) You must clean you room.2. Could you tell me the difference between "You are to finish the work by 4 pm" and "You must finish the work by 4 pm?"

You are to clean your room.
You are to finish the work by 4pm.

BillJI see these as a special kind of directive where I have the authority to tell you what you are going to do, and I leave you no choice.

I agree that that is very likely, but it's possible that somebody else has the authority:

Your mother has left me a list of your tasks for this evening. You are to clean your room, and then ...

To BillJ/fivejedjon:

Then, is "You are to clean your room" read only as "You must clean your room" to you?

lucas21c1. Can this sentence, "You are to clean your room", be interpreted as follows?(1) You are going to clean your room.(2) You must clean you room.

(1) No. (2) Yes.

But that doesn't mean that the is to idiom always means 'must'. It can occasionally mean "going to", especially in journalistic contexts (President Obama is to sign the