According to my book "English Grammar in Context" by Michael Vince "must" and "have to" can both be used but it does not say if in these examples either can also be used.

I read that in duties either "must" or "have to" can be used for example, "Everyone must/have recycle as much as possible." But in other examples "You must keep this door locked", an order "You must be more careful" and "You must return the books on time" (said by a librarian)and "visitors must report to reception on arrival" "must" is used because it's said by the person present. But "have to" can also be used if it's not said by the speaker present but if it's because of someone else or it is a law/rule. Is this right?

1 Answer 1


In terms of grammar, must or has/have to can be used in any of those examples, whether said by someone present or not.

The word must has a more formal, official feeling, and would likely be used in a written notice.

The phrase have to sounds less official, and could be more of a description or recommendation.

(In your example
"Everyone must/have recycle as much as possible."
the word have is incorrect. The form would be has to.)

  • Is "have to" used only if the speaker is not present in this situation? For example, (Doctor to patient) "It's really important to take this medicine three times a day " Should I use "must" or "have to"? "You must/have to take this medicine three times a day." Jun 11, 2021 at 6:26
  • It's from "English Grammar in Context" by Michael Vince. It's also mentioned in "Practical English Usage" by Michael Swan that if the obligation comes from someone else then "have to" is used but in modern English "must" is still used in such situations. But in the quoted example "the speaker" as Michael Vince says thinks it's important to take the medicine and suggests using "must". Can both be used here as well? Jun 11, 2021 at 6:26
  • The only correct answer it suggests is "You must take this medicine three times a day." Jun 11, 2021 at 6:34
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    As I suggested in my answer, "have/has to" could be a description or recommendation rather than an order. "Must" has the connotation of an order. In the doctor/patient example, the doctor could use either phrase. In a conversation, "you have to" is more likely. Jun 11, 2021 at 9:07
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    @AntoniaA I don't think the lines for "must/have to" are as sharp as that, at least not to me. If you want to see real examples of the uses, check google books. Jun 12, 2021 at 12:53

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