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Aren't "be supposed to" and "be to" the same?

  1. You are not to use the elevator.

  2. You are not supposed to use the elevator.

  3. You don't have to use the elevator

What's the main difference between "You are not to use the elevator." and "You don't have to use the elevator"?

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    Linking an older question with this. Chiefly because it is similar, and also because I was uncertain about my use of terminology, so an eventual reader of that question will benefit from taking a look at the answers here as well.
    – Jyrki Lahtonen
    Aug 26 at 20:34
  • Note that the first sentence is literally a command. Commands are quite different from other utterances.
    – Fattie
    Aug 28 at 13:56
  • Some here say they see all three examples as wholly natural, native English. I suggest that's more from reflex response and lack of consideration than anything else.
    – Robbie Goodwin
    Aug 31 at 22:50

3 Answers 3

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(1) is a direct command (you must not use it).

(2) means that, according to the rules, you should not use it (but the speaker didn't make the rules).

(3) means that you can use it, but you need not if you don't want to.

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    +1, but it may be worth noting that the *be*+infinitive construction isn't only for direct commands; for example, something like "It says here that we're not to leave it unattended" is closer in meaning to #2. (But obviously there's nothing like that in the OP's example.)
    – ruakh
    Aug 26 at 0:10
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    #2 also tends to carry an implicit "without good reason" wheras the first one is more of an absolute forbiddal.
    – Shadur
    Aug 27 at 13:23
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    An English learner who isn't sure of the meaning of "don't have to X" also may not know exactly what "need not (X)" means. Specifically: "need not X" does NOT mean the same as "need not to (X)" but rather more like "not need to (X)", that is, "are not required to do X".
    – LarsH
    Aug 28 at 13:27
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  1. ("You are not to use the elevator") means that you should not use the elevator; it is not allowed. Although the sentence is grammatically correct, it wouldn't usually be heard in everyday speech. It would be more natural to say "you must not use the elevator". Another alternative would be to say "using the elevator is forbidden".

  2. ("You are not supposed to use the elevator") is similar, although there's a bit of ambiguity. It means that there is a rule stating that one must not use the elevator. In spoken English, if 'supposed' was stressed, this could imply the speaker thinks there's a way around the rules ("you are not supposed to use the elevator...", but if you go in quietly without anyone noticing...)

  3. ("You don't have to use the elevator") means that there is no requirement to use the elevator (it is not compulsory to do so). However, the sentence implies that it is still perfectly permissible and within the rules. The focus of the sentence may instead be more on the options available, rather than the rules. It implies that there are alternatives available, so could be continued "you don't have to use the elevator", but can use the stairs or escalator if you prefer.

Finally, just to add that in British English, the word elevator is not used; 'lift' is the word for a machine that vertically transports people between floors of a building.

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    I thought Kate's Answer said it all but whv20 reminds me all three examples seem contrived; unnatural, unlikely to appear in real English. Where did they come from, please? To me it seems if you invented them yourself, that shows a fine imagination. If your teacher made them up that shows the same, but with a need for caution. If either of you found them published, can you say where?
    – Robbie Goodwin
    Aug 26 at 16:44
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    Interesting. As a native speaker of American English, I find all three examples to be perfectly natural. Not all of them are the most natural phrasing in all situations, but each has a situation in which using that sentence wouldn't raise an eyebrow. For example, #1 sounds rather formal and authoritarian, which is perfectly natural in certain situations but not in others.
    – LarsH
    Aug 28 at 13:33
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    "you are not to use the elevator" is a command. It means "I/we forbid you to use the elevator". In contrast "you must not use the elevator" is an opinion statement meaning "it is very important that you not use the elevator, something bad is likely to happen if you do".
    – David42
    Aug 28 at 15:01
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Here is my take on this as a UK speaker (with imagined context added in brackets)...

  • You are not to use the elevator (if there is a fire.)

This is a statement from someone in authority to someone junior. It is something that a teacher might say to a pupil. Or, as in my example, a safety notice. You are expected to obey.

  • You are not supposed to use the elevator. (But when you are carrying something heavy, it is hard to negotiate the fire-doors on the stairwell.)

This implies there is a rule or current practice that expects you to use the stairs, but the 'supposed' qualification suggests that (a) you are being addressed by an equal, and (b) the unspecified person that expects you to obey is probably someone else. It is likely the next word will be 'but' followed by an exception to the rule. There may be times and conditions when you are not expected to obey.

  • You don't have to use the elevator. (If you are only going up one floor it is faster to use the stairs.)

This could be taken as the reverse of the last statement: "You are supposed the elevator". It could be even milder. A hotel may have fancy lifts while the stairs are plain and hidden behind fire-doors, but you are free to use either. There is a suggestion that there is a common practice, and the speaker may be about to provide an exception to this.

None of this is in the grammar; all of this is in the use. Non-UK speakers may have a completely different take on this, as US speakers do with the phrase "I will do it presently".

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  • Sorry, Richard… all those logical caveats stopped that Answer having much to do with the examples in the Question.
    – Robbie Goodwin
    Aug 27 at 21:17
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    @RobbieGoodwin I could have written my answer differently: "The use of the passive exonerative are not supposed to distances the speaker from the one who supposes". This is the same argument but tarted up to look like grammar. I chose not to, because I feel the question was more about usage than exact grammar.
    – Richard Kirk
    Aug 28 at 7:46
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    I found the "logical caveats" to be very helpful in explaining the difference in meaning and typical usage of the three sentence patterns.
    – LarsH
    Aug 28 at 13:36
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    The difference between "you are not to" and "you don't have to" isn't just usage or assumptions; one is a command forbidding an action, and the other is permission to do other things, without forbidding the thing. You aren't required to use the elevator, but you still can if you want. (Other than that last paragraph, I think this answer is good, with likely contexts for usages of these phrasings.)
    – Peter Cordes
    Aug 28 at 17:03

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