Would you be kind enough tell me whether there is a sensible difference between the following sentences?
1.1. You mustn’t get your feet wet.
1.2. You are not to get your feet wet.
2.1. You must take one tablet before each meal.
2.2. You are to take one tablet before each meat.
3.1. You mustn’t say such things.
3.2. You are not to say such things.
4.1. They must know him.
4.2. They must have known him. restricts the situation to the past so implies the person they must have known is now no longer alive.
5.1. They must be waiting for you now (they are still waiting for you)
5.2. They must have been waiting for you yesterday/last week etc. (they are no longer waiting for you.)
Thank you in advance foir your efforts.
Re your first three pairs of sentences:
You are (not) to is much stronger than must. It corresponds to an order, whereas must (as you know) means it is necessary to... In fact, you have to be careful when you use this structure (You are (not) to) because it can cause offence. Particularly strict, overbearing parents sometimes use it when speaking to their children; teachers can use it when giving instructions to pupils; a doctor when explaining a prescription. It amounts to laying down the law.
Last edited by naomimalan; 21-May-2008 at 10:29.
Excuse me, but I think that
"you have to be careful when you use this structure (You are (not) to) because it can cause offence",
does not mean that "it is an offensive phrase which should be avoided by all means".