The V2 rule

In a Swedish main clause (huvudsats), the finite verb is always in second position. This is the most important word order rule. When something other than the subject starts the sentence, the subject moves after the verb (inversion).

Huvudsats (main clause)

Schema: Fundament — V1 — Subjekt — Satsadverbial — V2 — Objekt — Adverbial. The fundament (first position) can be filled by the subject, an adverbial, or an object.

Compare main clause (huvudsats) and subordinate clause (bisats) patterns.

Bisats (subordinate clause)

In a bisats, the satsadverbial comes before the verb: bisatsinledare — Subj — Satsadv. — V1 — V2 — Objekt — Adverbial.

Key differences

Huvudsats: Subj — V1 — inte — V2 (satsadv. after first verb).
Bisats: Subj — inte — V1 — V2 (satsadv. before first verb).
Compare: Jag förstår inte vs ...att jag inte förstår.