Learn Hardcore Dutch: In het artikel zegt de journalist dat open debat belangrijk is voor een vrije samenleving. - In the article the journalist says that open debate is important for a free society.

The basic order is: Subject – Verb – ...
De journalist zegt dat open debat belangrijk is...
If you move something to the front for emphasis (here: In het artikel), that takes the first position, and the verb still has to be in second position, so the subject moves after the verb:
- In het artikel (1st) zegt (2nd) de journalist (3rd) …

So zegt de journalist is just the result of verb-second word order, not a special stylistic inversion like in old-fashioned English.

Can I also say De journalist zegt in het artikel dat open debat belangrijk is...? Is there any difference?

Yes, that sentence is also correct. The difference is mainly one of emphasis and rhythm:

De journalist zegt in het artikel dat…
→ neutral; focuses first on who is saying it (the journalist).
In het artikel zegt de journalist dat…
→ slightly more emphasis on in the article (as opposed to on TV, in an interview, etc.).

Grammatically, both are fine. It’s common in Dutch to move time/place phrases like in het artikel, gisteren, op school to the front to vary the style.

Why is it het artikel and not de artikel?

In Dutch, nouns are either de-words (common gender) or het-words (neuter).

artikel is a het-word: het artikel
singular:
- het artikel
plural:
- de artikelen

There is no fixed rule that lets you always predict de vs het; you usually have to learn it with the noun. A dictionary will mark artikel as het artikel.

Why is it open debat without een? Could I say een open debat?

Both are possible, but they have different nuances:

open debat (no article)
→ talking about open debate in general, as a concept. Like English “open debate is important”.
een open debat
→ refers to one specific debate or a type of individual debate that is open:
We willen een open debat voeren (we want to have an open debate).

In your sentence, the idea is more general: the concept of open debate is important for a free society, so leaving out the article is natural.

What exactly is the function of dat in zegt de journalist dat open debat belangrijk is?

Here dat is a subordinating conjunction (a complementizer), similar to English that in “says that open debate is important”.

Main clause: In het artikel zegt de journalist …
Subordinate clause introduced by dat:
dat open debat belangrijk is voor een vrije samenleving

Important points:

This dat does not mean that one / that thing; it is not a pronoun here.
It introduces a clause which functions as the object of zegt (what does he say? → that open debate is important …).

Why is the verb is at the end of dat open debat belangrijk is? In English we say “that open debate is important”, not “important is”.

In Dutch subordinate clauses (clauses introduced by dat, omdat, als, wanneer, etc.), the conjugated verb goes to the end.

Main clause word order: Subject – Verb – (Other stuff)
Open debat is belangrijk.
Subordinate clause after dat: verb at the end
… dat open debat belangrijk is.

So belangrijk is is normal Dutch word order in a dat-clause. Putting is earlier would make it ungrammatical:
✗ dat open debat is belangrijk (wrong in standard Dutch).

Could I say dat open debat is belangrijk voor een vrije samenleving instead?

No, not in standard Dutch. Once you introduce the clause with dat, you must use subordinate clause word order, so the verb goes to the end:

✅ dat open debat belangrijk is voor een vrije samenleving
❌ dat open debat is belangrijk voor een vrije samenleving

If you want is right after open debat, you have to remove dat and make it a main clause:

Open debat is belangrijk voor een vrije samenleving.
(Here is is in the normal second position of a main clause.)

Why is it belangrijk and not belangrijke?

Dutch makes a distinction between:

Predicate adjectives (after zijn, worden, blijven, etc.)
→ usually no -e ending
- Het debat is belangrijk.
- Open debat is belangrijk.
Attributive adjectives (directly before a noun)
→ often with -e ending
- een belangrijk debat
- het belangrijke debat

In your sentence, belangrijk comes after the verb is and describes the subject open debat, so it’s a predicate adjective → belangrijk without -e.

Why does vrije have an -e, but belangrijk doesn’t?

Because they play different roles in the sentence:

belangrijk is a predicate adjective after is:
open debat (subject) – is – belangrijk (predicate)
→ no -e.
vrije comes directly before a noun (samenleving) and describes it, so it is an attributive adjective:
een vrije samenleving
→ here you normally add -e.

General rule (with some exceptions):
Attributive adjective in front of de-words and indefinite het-words → add -e: een vrije samenleving, de vrije samenleving, de belangrijke tekst.

Why is it een vrije samenleving and not een vrij samenleving?

Two reasons:

Word gender and article
samenleving is a de-word: de samenleving.
With a de-word in the singular after een, the attributive adjective takes -e:
- een vrije samenleving
- een grote samenleving
The rule is:
- de
  - adjective → adjective gets -e (de vrije samenleving)
- een
  - de-word
    - adjective → adjective gets -e (een vrije samenleving)
- het
  - adjective → adjective gets -e (het vrije land)
- een
  - het-word (singular, indefinite, no extra modifier) → often no -e (een vrij land)

Since samenleving is a de-word, you must say een vrije samenleving.

What does voor do in belangrijk is voor een vrije samenleving? Can I use another preposition?

Here voor means “for / in relation to / for the benefit of”, just like in English “important for a free society”.

belangrijk voor iemand/iets = important for someone/something
- belangrijk voor een vrije samenleving
- belangrijk voor de economie
- belangrijk voor mij

You cannot replace voor with aan, naar, or tegen here. belangrijk voor is the fixed and natural combination.