Questions & Answers about Det börjar mörkna i skogen nu.
How does the verb mörkna relate to the adjective mörk?
The suffix -na is used to turn adjectives into verbs that describe a change of state. By adding -na to mörk (dark), we get the inchoative verb mörkna, which means 'to become dark' or 'to darken'.
Why isn't there an att (to) before mörkna here?
The verb börja (to begin/start) is often followed directly by an infinitive verb without the particle att. You can absolutely say börjar att mörkna, but dropping the att is extremely common and natural in both spoken and written Swedish.
Why do we use det at the beginning of this sentence?
Swedish uses det as a 'dummy subject' for weather, time, and environmental conditions, exactly like how we say 'it is raining' or 'it is dark' in English. Since there is no specific person or thing making the forest dark, det fills the required subject spot in the sentence.
Why does the Swedish sentence use börjar instead of a direct translation for 'is starting'?
Swedish does not have a direct equivalent to the English present continuous tense (the 'is doing' form). The simple present tense börjar covers both 'starts' and 'is starting', and the ongoing nature of the action is made clear here by the context word nu (now).