Sjåføren må være edru.

Because Norwegian usually puts the definite article at the end of the noun instead of using a separate word like the.

• sjåfør = driver
• sjåføren = the driver

So -en is the definite singular ending here.

Må is a modal verb, like must, have to, or sometimes need to in English. Its infinitive form is måtte.

In this sentence, må expresses necessity or obligation: the driver is required to be sober.

Because after a modal verb like må, the next verb normally appears in the infinitive.

So:

• er = is / am / are
• være = to be

After må, Norwegian uses være:

• må være = must be

Not må er.

In Norwegian, modal verbs such as må, kan, skal, vil, and bør are normally followed by an infinitive without å.

So:

• å være = to be
• but må være = must be

This is similar to English, where we say must be, not must to be.

Edru is an adjective. It describes the state of the driver.

In this sentence it comes after være, so it is a predicate adjective:

• Han er trøtt = He is tired
• Sjåføren må være edru = The driver must be sober

So edru is not an adverb or a verb; it is describing the subject.

Yes, but it means something different.

• Sjåføren er edru = The driver is sober
• Sjåføren må være edru = The driver must be sober

The first sentence states a fact. The second expresses a requirement, rule, or necessity.

Yes. In Norwegian, må være can sometimes express a logical conclusion, not just an obligation.

For example:

• Han må være hjemme nå. = He must be at home now.

That could mean I conclude that he is at home, not he is required to be at home.

In Sjåføren må være edru, the most natural meaning is usually obligation/requirement, especially because of the word edru and the real-world context.

This is normal Norwegian main-clause word order:

• Sjåføren = subject
• må = finite verb
• være = infinitive
• edru = complement

Norwegian main clauses usually follow the verb-second pattern, meaning the finite verb is in the second position. Here, the subject comes first, so the finite verb må comes next.

A rough English-style guide would be:

SHAW-fuh-ren moh VAIR-uh EH-droo

A few useful notes:

• sj in sjåføren sounds like sh
• å sounds somewhat like the vowel in saw
• ø has no exact English equivalent; it is a rounded front vowel
• edru has stress on the first syllable

This is only an approximation, but it can help you get started.