Learn Hardcore Norwegian: Hun viser sin sårbare side, og det styrker tilliten mellom oss. - She shows her vulnerable side, and it strengthens the trust between us.

sin – with masculine or feminine singular nouns
- sin bil (his/her car)
- sin side (his/her side)
sitt – with neuter singular nouns
- sitt hus (his/her house)
sine – with all plural nouns
- sine venner (his/her friends)

So in Hun viser sin sårbare side, we use sin because side is feminine singular, not because hun is feminine.

Why is it sårbare and not sårbar in sin sårbare side?

In Norwegian, when an adjective stands in front of a noun with a preposed possessive (like min, din, sin, vår), the adjective normally takes the definite form (ending in -e for most adjectives).

Compare:

en sårbar side – a vulnerable side (indefinite, no possessive)
den sårbare siden – the vulnerable side (definite, with article)
min sårbare side / sin sårbare side – my/her vulnerable side (with possessive before the noun)

So:

en sårbar side
sin sårbare side ← adjective gets -e because of the possessive in front

Sin sårbar side would be ungrammatical in standard Norwegian.

What gender is side, and how would it look with an article?

Side is grammatically feminine, but in Bokmål it is often treated as common gender (like masculine). So you normally see both patterns:

Feminine pattern:
- ei side – sida
Common/masculine pattern:
- en side – siden

With a possessive in front, the article disappears, so we get:

sin sårbare side

From this sentence alone, you cannot see whether the speaker normally prefers ei side or en side.

In og det styrker tilliten mellom oss, what does det refer to, and why is it neuter?

Here det refers to the whole action or situation described in the first clause: the fact that she shows her vulnerable side.

Norwegian uses neuter det as a pronoun for an entire statement, situation, or idea, similar to English “that” or sometimes “it”:

Hun viser sin sårbare side, og det styrker tilliten mellom oss.
= She shows her vulnerable side, and that strengthens the trust between us.

We don’t use den here because we are not talking about the specific noun side anymore, but about the situation as a whole.

Could I say Hun viser hennes sårbare side, and what would that mean?

You can say Hun viser hennes sårbare side, but it changes the meaning:

Hun viser sin sårbare side.
= She shows her own vulnerable side.
Hun viser hennes sårbare side.
= She shows another woman’s vulnerable side.

So you only use hennes (or hans) when the possessor is someone other than the subject in that clause. For something that belongs to the subject, you use sin/sitt/sine.

Why is it tilliten and not just tillit? What nuance does the definite form give in styrker tilliten mellom oss?

Tillit = trust (in general).
Tilliten = the trust (some specific trust that exists or is being talked about).

In styrker tilliten mellom oss, the definite form suggests:

there is already some relationship and some trust between oss,
that particular mutual trust is what is being strengthened.

Saying just styrker tillit mellom oss would sound strange and unidiomatic; after mellom oss you nearly always use the definite: tilliten mellom oss (“the trust between us”).

Does tillit have a plural? How would I talk about “trusts” or “levels of trust”?

In normal usage, tillit is an uncountable noun and is not used in the plural. You basically keep it in the singular:

mye tillit – a lot of trust
lite tillit – little trust
tilliten mellom oss – the trust between us

If you need to talk about different kinds or degrees of trust, you usually rephrase:

ulike former for tillit – different forms of trust
forskjellige nivåer av tillit – different levels of trust

A plural like *tilliter is not used in standard language.

What is the difference between mellom oss, blant oss, and oss imellom?

They all involve more than one person, but the usage differs:

mellom oss – between us
- Used for relationships, interaction, or something that exists between specific people.
- tilliten mellom oss – the trust between us.
blant oss – among us
- Used for something distributed within a group.
- Det er mye mistillit blant oss. – There is a lot of distrust among us (in our group).
oss imellom – literally “us between”, idiomatic “between you and me / between us two”
- Slightly more idiomatic/colloquial, often with a nuance of confidentiality.
- Dette blir mellom oss / oss imellom. – This stays between us.

In tilliten mellom oss, mellom oss is the normal and natural choice.

Why is the word order det styrker tilliten and not something like det tilliten styrker?

Norwegian main clauses follow the V2 rule: the finite verb must be in second position in the clause.

In det styrker tilliten:

det – subject (first element)
styrker – finite verb (must be second)
tilliten – object (comes after the verb)

So the normal order is subject – verb – object:

Det styrker tilliten (mellom oss).

Forms like det tilliten styrker would be ungrammatical in a normal statement. Only in questions or some special emphasis structures do you move the verb to the very front:

Styrker det tilliten mellom oss? – Does it strengthen the trust between us?

Why is there a comma before og in this sentence?

Norwegian usually puts a comma between two independent main clauses joined by og:

Hun viser sin sårbare side, og det styrker tilliten mellom oss.
- Clause 1: Hun viser sin sårbare side.
- Clause 2: Det styrker tilliten mellom oss.

Each clause has its own subject and verb, so they are grammatically complete on their own. In that case, the standard rule is: comma before og.

If og just connects parts inside one clause (e.g. two nouns or two verbs with one subject), you do not use a comma:

Hun viser styrke og sårbarhet. (no comma)

If the subject were jeg instead of hun, how would the first part of the sentence change?

Then you would no longer use the reflexive sin, because that form only exists for the 3rd person. For jeg, you use min:

Hun viser sin sårbare side …
→ Jeg viser min sårbare side, og det styrker tilliten mellom oss.

So:

3rd person subject: Hun viser sin sårbare side.
1st person subject: Jeg viser min sårbare side.