Learn Icelandic: Það er dimmt inni.

In Icelandic, það (it) is used as a "dummy subject" for general conditions, atmosphere, and weather. Just like in English when we say "it is dark," there isn't a specific object doing the action. Það simply steps in to give the sentence a subject.

Why is the adjective spelled dimmt instead of dimmur?

Adjectives in Icelandic have to match the gender of the word they describe. Because the dummy subject það is a neuter pronoun, the adjective has to be in the neuter form. The neuter form of dimmur (dark) is dimmt.

Why use inni instead of í for "inside"?

Í is a preposition meaning "in", and it needs to be followed by a noun (like "in the room"). Inni is an adverb meaning "inside" or "indoors". Since we are just describing a location without pointing to a specific object, we use inni on its own.

What happens to það if I change the word order to say "Inside, it is dark"?

If you put inni at the start of the sentence, the verb er must come right after it to follow the strict Icelandic "verb-second" rule. When the dummy subject það gets pushed out of the first position, it is usually dropped completely. The sentence becomes: Inni er dimmt.