Breakdown of I dag er han på biblioteket.
være
to be
han
he
i dag
today
på
on / at / in (a language) / of (after nouns like end or start)
Questions & Answers about I dag er han på biblioteket.
Why do we use på instead of i for the library?
In Danish, the preposition på is often used for public institutions or places where you go for a specific service, like a library, a hospital, or a train station. Even if he is physically inside the building, you say på biblioteket to mean "at the library".
Why is the word order er han (is he) instead of han er (he is)?
This happens because of the Danish V2 rule, which says the main verb must be the second piece of information in a sentence. Since the time phrase I dag (today) takes up the first spot, the verb er (is) must come next, pushing the subject han (he) to the third spot.
How does the word biblioteket mean "the library"?
In Danish, the word for "the" is usually attached to the end of the noun. The word for "a library" is et bibliotek (an et-word). To say "the library", you take that et and attach it to the end, making it biblioteket.
The lesson is about prepositions of location. Is the i in I dag also a preposition of location?
No, in this case, i is used as a preposition of time. I dag is a fixed phrase that simply means "today". You will see i used in many time expressions, like i morgen (tomorrow) and i aften (tonight).