Learn Swedish: Familjen somnar tidigt på kvällen. - The family falls asleep early in the evening.

The verb somnar is a classic inchoative verb, which means it describes entering a new state. It is related to the noun sömn (sleep). The -na ending indicates the process of transitioning into that state, which is why it translates to falling asleep.

Could I use sover instead of somnar in this sentence?

You could, but it would change the meaning. Sover describes the ongoing state of sleeping. If you said Familjen sover tidigt, it would mean the family sleeps early. Somnar specifically highlights the transition of falling asleep.

Why does tidigt have a -t at the end?

Here, it acts as an adverb modifying the verb somnar, telling us when the action happens. In Swedish, adverbs are typically formed by adding a -t to the base adjective tidig.

Why do we use the definite form kvällen in the phrase på kvällen?

When referring to a general or recurring part of the day, Swedish uses the preposition på plus the definite form of the noun. So på kvällen naturally translates to 'in the evening' or 'in the evenings'.