Learn Hardcore Norwegian: Jeg må bytte kontorstol fordi den gamle ikke gir nok ryggstøtte. - I have to change office chair because the old one does not give enough back support.

må focuses on obligation or something that really must happen (for health, rules, situation).
trenger focuses on the fact that something is needed or lacking.

You could say:

Jeg trenger å bytte kontorstol.
This is grammatically fine, but in everyday Norwegian Jeg må bytte kontorstol is more natural when you’re talking about a necessary action you will actually take.

Why is it kontorstol and not kontor stol? How do these compounds work?

Norwegian, like other Germanic languages, loves compound nouns:

kontor = office
stol = chair
kontorstol = office chair

When two nouns together form a new, fixed concept, they are usually written as one word in Norwegian. Writing kontor stol would be wrong and look like two separate words: office and chair, not the combined concept office chair.

Other similar examples:

skrivebord (skriv + bord) = desk
solbriller (sol + briller) = sunglasses
badehåndkle (bade + håndkle) = bath towel

Why is it kontorstol and not kontorstolen (with the definite ending)?

Norwegian marks definiteness on the noun:

en kontorstol = an office chair
kontorstolen = the office chair

In Jeg må bytte kontorstol, we’re talking about the type of thing you’re replacing, not about a specific, already‑identified chair. This is similar to English:

English: I have to change *office chair.* (no article)
Norwegian: Jeg må bytte kontorstol.

If you wanted to be specific, you could say:

Jeg må bytte kontorstolen
= I have to change the office chair (a particular one both speaker and listener know about).

Why is it den gamle and not det gamle?

Den is the pronoun used for masculine and feminine nouns.
Det is used for neuter nouns.

The word stol (and kontorstol) is masculine:

en stol / en kontorstol (a chair / an office chair)
stolen / kontorstolen (the chair / the office chair)
den gamle (the old one) – referring back to (kontor)stol

So we say:

Jeg må bytte kontorstol fordi den gamle ikke gir nok ryggstøtte.
= …because the old one (masc. = the old chair) doesn’t give enough back support.

If the noun had been neuter, for example bord (table):

et bord – det gamle (the old one, neuter).

Why is the adjective gamle and not gammel in den gamle?

Norwegian adjectives have two main forms in the singular:

Strong form (no article/demonstrative):
- en gammel stol = an old chair
Weak form (with a determiner like den, det, de, min, denne, etc.):
- den gamle stolen = the old chair
- den gamle = the old one

In den gamle, the pronoun den functions like a determiner, so the adjective takes the weak form gamle.

Compare:

en gammel kontorstol (a old office chair)
den gamle kontorstolen (the old office chair)
den gamle (the old one – chair understood from context)

How does den gamle work without repeating kontorstol? Is that normal?

Yes, this is very normal and very common. Den gamle here is a pronoun + adjective combination that stands for den gamle kontorstolen:

Full version: …fordi den gamle kontorstolen ikke gir nok ryggstøtte.
Natural shortened version: …fordi den gamle ikke gir nok ryggstøtte.

Norwegian does this a lot to avoid repetition, exactly like English the old one:

English: I bought a new chair because *the old one was broken.*
Norwegian: Jeg kjøpte en ny stol fordi den gamle var ødelagt.

Why is it fordi den gamle ikke gir… and not fordi ikke den gamle gir…? Where does ikke go?

In Norwegian subordinate clauses (clauses starting with fordi, at, hvis, etc.), the basic word order is:

[subordinator] + subject + (adverb like ikke) + verb + …

So:

fordi den gamle ikke gir nok ryggstøtte
- fordi = because
- den gamle = subject
- ikke = negation
- gir = verb

That follows the rule: subject → ikke → verb.

Compare with a main clause, where the finite verb is in second position and ikke normally comes after the verb:

Main clause: Den gamle gir ikke nok ryggstøtte.
(subject – verb – ikke – rest)
Subordinate clause: …fordi den gamle ikke gir nok ryggstøtte.
(subordinator – subject – ikke – verb – rest)

Putting ikke before the subject, fordi ikke den gamle gir…, would sound wrong in standard Norwegian.

What is the difference between fordi and for when they mean “because”?

Both can be translated as because, but they’re not interchangeable.

fordi = because (neutral, most common, used everywhere)
for = because (more like for / for in older or more literary English; also often comes after a pause, sometimes with a comma)

Examples:

Jeg må bytte kontorstol fordi den gamle ikke gir nok ryggstøtte.
(completely normal, neutral)
Jeg må bytte kontorstol, for den gamle gir ikke nok ryggstøtte.
(also correct, but feels a bit more written/literary or explanatory; there’s usually a comma before for)

As a learner, default to fordi for “because” in most situations.

What does nok mean in ikke gir nok ryggstøtte, and why is it placed there?

Nok here means enough:

nok ryggstøtte = enough back support

The structure is:

ikke gir nok ryggstøtte
= does not give enough back support

So:

gir nok ryggstøtte = gives enough back support
ikke gir nok ryggstøtte = does not give enough back support

The ikke negates the verb gir (gives), not nok directly. Sounds like:

[the old one] does not [give enough back support].

You would not normally say gir ikke nok ryggstøtte inside this subordinate clause, because inside a subordinate clause the pattern is subject – ikke – verb:

den gamle ikke gir nok ryggstøtte (correct in a fordi-clause)

In a main clause, you’d say:

Den gamle gir ikke nok ryggstøtte.
(subject – verb – ikke – …)

What exactly is ryggstøtte, and how is it formed?

Ryggstøtte is another compound noun:

rygg = back (body part)
støtte = support

Together:

ryggstøtte = back support / lumbar support

It can mean either the physical backrest on a chair or back support in a more general sense, depending on context. In this sentence it clearly refers to the back support of the office chair.

Grammar:

en ryggstøtte = a back support
ryggstøtten = the back support

Could I say gir nok støtte til ryggen instead of gir nok ryggstøtte?

Yes, that’s possible and understandable:

…fordi den gamle ikke gir nok støtte til ryggen.
= because the old one doesn’t give enough support to the back.

But ryggstøtte is shorter and more idiomatic when talking about chairs and ergonomics. A native speaker would usually say:

god ryggstøtte = good back support
dårlig ryggstøtte = bad back support
nok ryggstøtte = enough back support

Why is there no possessive like min in Jeg må bytte kontorstol? How would I say “my office chair”?

Norwegian often leaves out the possessive when it’s obvious from context that you’re talking about your own item:

Jeg må bytte kontorstol.
= I have to change (my) office chair.
(It’s normally understood that it’s your chair.)

If you really want to emphasize my, the most natural way is to put the possessive after the noun:

Jeg må bytte kontorstolen min.
= I have to change my office chair.

Using min before the noun is possible but often sounds more marked/emphatic or even a bit un‑Norwegian in everyday speech:

Jeg må bytte min kontorstol. – grammatically okay, but not how people usually say it.

So the three main options, from most to least common here, are:

Jeg må bytte kontorstol. (possessor understood)
Jeg må bytte kontorstolen min. (my office chair)
Jeg må bytte min kontorstol. (emphatic, less natural in this everyday context)