Hun må sy inn jakken.

Sy inn is a set expression meaning to take in a piece of clothing by sewing it so it becomes narrower or smaller.

So Hun må sy inn jakken means she needs to alter the jacket because it is too big or too loose in some way.

Because after a modal verb like må (must / have to), Norwegian normally uses the next verb in the bare infinitive, without å.

So:

• Hun må sy inn jakken = correct
• Hun må å sy inn jakken = not correct

This is similar to English:

• She must sew it in
• not She must to sew it in

Here, inn is not just the literal word in. It is part of the particle verb sy inn.

Together, sy inn has a specific meaning: alter by sewing inward / take in.

A lot of Norwegian verbs work like this, where a small word such as inn, ut, opp, or på changes the meaning of the verb:

• sy = sew
• sy inn = take in by sewing
• sy på = sew on

So in this sentence, you should learn sy inn as a unit.

Jakken means the jacket, with the definite ending -en.

Norwegian often uses the definite form when talking about a specific, known object. So this sentence is about a particular jacket, not just any jacket.

Compare:

• jakken = the jacket
• en jakke = a jacket

In this sentence, the speaker assumes both people know which jacket is meant.

The structure is:

• Hun = subject
• må = finite modal verb
• sy = infinitive main verb
• inn = particle
• jakken = object

So the pattern is:

subject + modal verb + infinitive + particle + object

This is a very common Norwegian structure.

Not always exactly, but in many sentences it can be translated as either must or has to.

In this sentence, må expresses necessity/obligation:

• Hun må sy inn jakken = She must take in the jacket / She has to take in the jacket

In natural English, has to is often the more everyday translation, while must can sound a bit stronger or more formal.

Because inn belongs closely with sy as part of the particle verb sy inn.

With a full noun like jakken, this order is very natural:

• sy inn jakken

If the object is a pronoun, Norwegian usually puts the pronoun before the particle:

• Hun må sy den inn = She has to take it in

So:

• sy inn jakken = normal with a noun
• sy den inn = normal with a pronoun

Because after må, the main verb stays in the infinitive.

• infinitive: sy
• present tense: syr

Compare:

• Hun syr. = She sews / is sewing.
• Hun må sy. = She must sew.

So the modal verb må is the conjugated verb, and sy stays in the infinitive.

These two words can be tricky for English speakers.

• må has a long vowel somewhat like the vowel in British more, but not exactly the same.
• sy has the Norwegian y sound, which does not exist in standard English. It is a rounded front vowel.

A useful trick for y:

1. Say ee as in see
2. Keep your tongue in that position
3. Round your lips

That gives you something close to the Norwegian y.

So:

• må ≈ moh
• sy ≈ a rounded-lips version of see

Taken literally, yes: Hun må sy inn jakken means she must sew the jacket in herself.

If you want to say that she needs to have it altered by someone else, Norwegian often uses a different structure, for example with få:

• Hun må få sydd inn jakken = She has to have the jacket taken in

So your sentence most naturally suggests that she herself is the one doing the sewing.