Henni finnst kjóllinn ljótur.

Because finnast often takes the experiencer in the dative case, not the nominative.

So in this sentence:

• henni = to her / she as the person having the opinion
• kjóllinn = the thing being judged
• ljótur = ugly

A very literal breakdown is:

• Henni = to her
• finnst = seems / is found
• kjóllinn = the dress
• ljótur = ugly

So the structure is closer to To her, the dress seems ugly than to ordinary English She thinks the dress is ugly.

Here finnst means something like:

• seems
• is considered
• is found
• idiomatically, thinks

So Henni finnst kjóllinn ljótur means She thinks the dress is ugly.

A more literal translation would be The dress seems ugly to her.

This is a very common Icelandic way to express opinions, impressions, and personal judgments.

Because the dictionary form is finnast, not finna.

These are different verbs in use:

• finna = to find, feel, discover
• finnast = to seem, be thought, be felt

The -st form is related to the Icelandic middle voice, but in many common verbs it is best learned as part of the verb itself.

So:

• ég finn = I find / I feel
• mér finnst = I think / it seems to me

In this sentence, finnst is the 3rd person singular present form of finnast.

Because with finnast, the thing that seems a certain way is the grammatical subject.

In this sentence:

• henni is the experiencer in the dative
• kjóllinn is the grammatical subject in the nominative

That is why kjóllinn is in the nominative form, and why the adjective ljótur agrees with kjóllinn, not with henni.

So even though English says she thinks..., Icelandic grammar is built more like:

To her, the dress seems ugly.

Because kjóllinn means the dress.

In Icelandic, the definite article is usually attached to the end of the noun:

• kjóll = a dress / dress
• kjóllinn = the dress

So the sentence is specifically talking about the dress, not just a dress in general.

Because ljótur has to agree with kjóllinn.

Kjóllinn is:

• masculine
• singular
• nominative

So the adjective also appears in the:

• masculine
• singular
• nominative

form: ljótur

This is called adjective agreement.

Because ljótur is not a direct object form here. It is a predicate adjective.

In other words, it is describing what kjóllinn is like, not acting as a separate object.

So:

• kjóllinn = nominative subject
• ljótur = predicate adjective agreeing with the subject

That is why both are nominative.

This is similar in function to English The dress is ugly, where ugly describes the subject.

Not exactly. Icelandic does not need an extra to be verb here.

The verb finnast can directly combine with a noun phrase and an adjective:

• Henni finnst kjóllinn ljótur.

This already means She thinks the dress is ugly.

So you should learn this as a normal Icelandic sentence pattern, not as a shortened version with a missing er.

Icelandic main clauses usually follow a verb-second pattern.

Here the order is:

1. Henni
2. finnst
3. kjóllinn
4. ljótur

The first element is henni, and then the finite verb finnst comes second.

This is a very natural order because henni is the person whose opinion matters, so it is a good topic for the start of the sentence.

You can also move things around for emphasis, but the verb still tends to stay in second position in main clauses.

It is very close in meaning, but the Icelandic structure feels a bit more like:

• The dress seems ugly to her
• She finds the dress ugly

So it expresses her personal impression or opinion.

In normal translation, She thinks the dress is ugly is the best natural English equivalent, but the Icelandic grammar is built differently.

You keep the same pattern and change the dative pronoun:

• Mér finnst kjóllinn ljótur. = I think the dress is ugly.
• Þér finnst kjóllinn ljótur. = You think the dress is ugly.

So a very useful pattern to memorize is:

• Mér finnst ...
• Þér finnst ...
• Henni finnst ...
• Honum finnst ...

This pattern is extremely common in Icelandic.