Learn Swedish: Vi måste hämta boken tidigare. - We must fetch the book earlier.

Just like in English, Swedish modal verbs like måste (must) are followed directly by the infinitive form of the next verb without using att (to). You say måste hämta (must fetch), never måste att hämta.

How does the word tidigare fit into our lesson on time adverbs?

Tidigare means 'earlier' and is the comparative form of the time adverb tidigt (early). Like idag (today) or nu (now), it often goes at the end of a simple sentence to describe when an action happens.

Why does the sentence use boken instead of just bok?

Bok is the base word for 'book'. To say 'the book', Swedish attaches the article to the end of the word. Because bok is an 'en-word', we add -en to the end to get boken.

If the subject was 'jag' (I) instead of 'vi' (we), would måste change its form?

No, Swedish verbs do not change based on the subject. Whether it is vi måste (we must) or jag måste (I must), the verb stays exactly the same.