Hi Sergey, this is one of those situations where English people tend to 'break the rules'! We use 'must' as a strong 'obligation', either as something we have committed ourselves to doing, or perhaps as an order, e.g. 'I must get on with my work.' 'You must get that ceiling fixed.' 'You must be careful when you drive in the dark.' So we use it as an imperative. But, we also use it as an assumption, e.g 'You must think I'm mad!' "You must be cold if the heating is broken.' This breaks the grammar rule of only using it when we have clear evidence that something is true. (So for instance, although the heating is broken, it is not necessarily true that you are cold, therefore it would be grammatically incorrect to use 'must' in this instance, even though we do actually use it this way in speech.) Likewise, we break the grammar rule with 'have to'. As with 'must' we use it as a way of talking about something we have committed ourselves to do, e.g. I have to go shopping (- or else we'll have nothing to eat tonight.) This again goes against the grammar rule, which states that 'have to' indicates an external demand, and is usually an imperative :-( Also, when used in speech, there is an implication of 'time' when we reverse the given grammar rules. We tend to use 'must' when something absolutely has to happen & has to happen soon, and 'have to' when it has to be done but can happen at an undefined time. E.g. 'I must leave now, to pick my son up from school' = urgent/defined time. 'I have to go shopping, or we'll have nothing to eat tonight' = not so urgent, as long as I do actually do the shopping before dinner time. I hope that helps, if not, please feel free to contact me for more explanation/examples. (An idiomatic expression for when we are confused about something: 'It's as clear as mud!' - meaning, it really isn't very clear at all!)

Hello Sergey, As you say this is an often asked question and in my training I remember being taught that actually these days (with very few exceptions) they can be used interchangeably. 'Must' tends to be more common in written English and 'have to' in spoken English. Hope this helps Bob

To me, the difference between "must" and "have to" in modern English comes down to formal vs. informal speech. "Must" sounds stronger and seems more formal but it is used much less than "have to" in everyday speech. I rarely hear "must" being used in the spoken word except, perhaps, when someone is emphasizing the obligation to do so something: "You have to do this." vs. "You must do this." The first is informal language and common. The second example sounds more formal and forceful. However, they are identical in meaning. Perhaps a linguistics expert has a more in-depth explanation, but my intuition as a native-speaker should be valid.

https://www.englishgrammarsecrets.com/musthaveto/menu.php Hi, I found the link above, hope it helps. If you use them in positive present form, differences are subtle, I wouldn't worry much about it!