Должен играть, и на компьютере, а не на скрипке? Это что-то новенькое.

да уж 🙄

HAVE TO. If you use must, it means должно быть

Thank you!
"FOR four hours a day" - is it correct?

If you use must, it means должно быть

Что значит "должно БЫТЬ" в данном контексте и что тогда такое must be?

FOR is correct

I thought должно быть meant MUST in assumptions

Да, но почему нельзя сказать he must play? Я думал, это то же самое, что и he has to, только сильнее.
Are you saying that this sounds like assumption?

Absolutely. In Modern English, we don’t use MUST as often as we use HAVE TO - in fact, we almost exclusively use it to express assumptions.

So if this kid wasn’t sure exactly how long he plays every day, but he knows it’s a long time, he can guesstimate by saying “I must play for four hours at a time” with a meaning of PROBABLY.

интересно...
Для меня he has to - это что-то вроде "ему следует", т.е. не совсем обязательно

That would be HE SHOULD

HAVE TO implies that you have no choice

The only time we use MUST for “have to” is when we emphatically recommend something: “You MUST see this movie!”

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спс за перводы