In English, we differentiate between “must” and “have to”. “Must” is generally considered more formal and authoritative, whereas “have to” may be interpreted more colloquial and less hard.

Swedish, on the other hand, uses måste in all contexts. For Swedes, it’s just an ordinary, statusless modal verb. Måste used in the same way as “must” or “have to” in English:

Jag måste skynda mig!
I have to hurry!

Du måste lämna in din nyckel senast den första februari.
One must hand in your key on the first of February at the latest.

Negatives:  In the negative, måste inte does not mean “must not” – it means “do/does not have to”:

Du måste inte åka om du inte vill.
You don’t have to go if you don’t want to.

Medborgare uppmanas att lämna information till polisen, men de måste inte.
Citizens are requested to leave information to the police, but they aren’t required to.

Past tense:  Technically, måste has a past form, which is also måste – but in modern Swedish, it is more common to use blev tvungen as the past form of måste. Tvungen is an outdated past participle form of att tvinga “to force” which has survived in blev tvungen.¹ Tvungen is declined (i.e., its form is changed) based on gender and number of the subject “having to” do something:

Jag blev tvungen att skynda mig.
I had to hurry.

Barnet blev tvunget att äta sina grönsaker trots allt.
The child had to eat her vegetables despite everything.

Blev ni tvungna att betala fullt pris?
Did you guys have to pay full price?

Tvungen, tvunget and tvungna are the only three forms of tvungen – tvungna is plural for both en-words and ett-words.

(¹Note: The modern past participle form of att tvinga “to force” is tvingad/tvingat/tvingade. If you say Jag blev tvingad, the meaning is “I was forced (to)”.)

“Have had to” and “had had to”:  Finally, the perfect forms of måste are har/hade blivit tvungen:

Vi har tidigare blivit tvungna att visa upp leg.
We have earlier had to present ID.

Han hade inte blivit tvungen att posta den.
He hadn’t had to send it by post.

Simple enough! Have fun 🙂