Learn Icelandic: Hefur þú aldrei séð norðurljósin? - Have you never seen the northern lights?

In Icelandic present perfect questions, adverbs like aldrei (never) or ekki (not) are placed right after the subject (þú) and before the main verb's past participle (séð). Notice that this matches the English word order perfectly: "Have you never seen...".

If I wanted to make this a statement instead of a question, where would aldrei go?

If you say "You have never seen the northern lights", the subject and the helper verb swap places, but the adverb stays safely sandwiched between the helper verb and the main verb. It becomes: Þú hefur aldrei séð norðurljósin.

Why do we use the form séð here?

séð is the past participle of the verb sjá (to see). Whenever you form the present perfect tense with the helper verb hafa (to have), the main verb must be in this specific neutral form, which is often called the supine.

How does the word norðurljósin break down to mean "the northern lights"?

It is a compound word made of norður (north) and ljós (lights). The -in at the very end is the attached definite article for neuter plural nouns, which translates to "the" northern lights instead of just "northern lights".