You must drive on the left in Great Britain.

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New Member
Hello everyone, this is my first message here but this place has been really usefull for me for a long time so thank you!

I thought the main difference between "have to" et "must" was that "have to" is about an external obligation and "must" an internal obligation.
But I've seen this sentence " You must drive on the left in Great Britain ". Yet it is an obligation caused by the law, so an external obligation isn't it?

I'm a bit confused on that point can you help?
  • Omelette

    Senior Member
    UK English
    This seems to cause a lot of confusion and it's discussed elsewhere on the English-only forum
    Must vs have to

    Though there can be times when 'have to' and 'must' have different uses, I would say in sentence like that - when you are talking about a rule - then they are interchangeable.
    'You must/have to drive on the left'.
    'Citizens must/have to pay their taxes'.
    'You must/have to pass your exams or you can't go to university'
    Last edited:


    Senior Member
    English UK
    Hello limitless92: welcome to the forums!

    I think there's more than a degree of truth in the distinction drawn by 'English as a Second Language' textbooks between have to = external compulsion and must = internal compulsion.

    But I think you should see it only as a guideline, not as a hard-and-fast 'rule'.

    That said, I find the sentence "You must drive on the left in Great Britain" rather odd - or antiquated. I can't imagine ever saying or writing it.


    Signal Modulation
    English - Scotland
    Passengers must not put their feet on the seats. I have to think. You must come with me. I have to try harder. When I said that they were interchangeable I meant simply in terms of internal/external obligation.


    Senior Member
    English UK
    Do you also find "You must drive on the left in Great Britain" odd?

    Keith Bradford

    Senior Member
    English (Midlands UK)
    I've just Googled "highway code" "drivers must" and got 53,000 hits, originating from both the UK and USA. And until today I'd never heard of the "rule" about internal/external compulsion.

    Conclusion: like most so-called "rules" of English, it's a statistical probability, not a dictum that must be followed.


    Senior Member
    English - British
    The distinction between internal and external compulsion for "must" and "have to" is completely new to me too. I don't recognise it in my own experience. What about "got to"? They are all used as equivalents in basic meaning, but they have differences of tone and register. Context, as ever, makes all the difference.


    Senior Member
    UK English
    I think 'must' and 'have to' can be used differently in certain sentences, even if the difference is relatively subtle.
    'I must remember to call my mother' is likely to mean 'I don't want to forget to call my mother' - it's my wish not to forget.
    'I have to remember to call my mother' is more likely to mean 'I feel obliged to call my mother' - whether I want to or not.
    This seems to be the origin of the 'rule' referred to in the initial question, but as others have stated, the two options are often interchangeable.


    Senior Member
    I think "must" works best with things that are absolute and not subject to change, whereas "have to" is more "ad hoc", or related to circumstances.

    "You must drive on the left in Great Britain" seems like an odd sentence to me, but I am not sure why. I would probably just say "In Great Britain you drive on the left."

    Compared with "You have to drive on the left in Great Britain", "You must..." seems to suggest that you have to drive whenever you are there, but "seems to suggest" is not saying much in this case.

    Pedro y La Torre

    Senior Member
    English (Ireland)
    This is a sign to be found on many Irish roads, advising foreigners to drive on the left. No ''must'' or ''have to'' there, but it still wouldn't shock me to see a sign stating, ''You must drive on the left in Ireland''.


    Senior Member
    I think 'must' and 'have to' can be used differently in certain sentences.
    I fully agree with this, and would like to give some example.

    This party is marvelous, so I must ("have to'" doesn't suit here) stay until it finishes.
    But my wife has been calling me for hours, so I have to ("must" also suits here) leave now.


    Senior Member
    British English
    With no further context I see this possible distinction:

    You must drive on the left in Great Britain
    is a command that you do so; a rule.

    You have to drive on the left in Great Britain means that you are physically compelled/constrained to do so by virtue of the road system and/or because it is a rule.

    In fact, the two mostly mean the same with regard to driving: a rule. 'Have to' does not necessarily mean that it is a rule or law but in the context of driving it almost always will.
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