Questions & Answers about Hän vammautui ja hänen täytyi jäädä sänkyyn.
This lesson focuses on the -ntua / -ntyä suffix for "becoming" something. Why does this sentence use vammautui?
You actually could use a -ntua verb here! The verbs vammaantua and vammautua are direct synonyms. They are both derived from the noun vamma (injury), and both mean "to get injured." Finnish frequently uses parallel inchoative ("becoming") suffixes like -ntua and -utua to accomplish the exact same thing.
Why does the second half of the sentence use the genitive hänen instead of the nominative hän?
The verb täytyä (to have to) is a necessity verb. In Finnish, necessity verbs strictly require their subject to be in the genitive case. Even though the verb is in the past tense (täytyi), the rule remains the same, so hän becomes hänen.
In English, we can just say "He got injured and had to stay in bed," omitting the second "he." Why must we include hänen in Finnish?
In Finnish compound sentences, you can generally only drop the pronoun in the second clause if the grammatical case of the subject remains exactly the same. Because the first clause takes a nominative subject (hän) and the second clause demands a genitive subject (hänen), you are forced to explicitly state the pronoun again.
Since he is staying "in" bed, why is the word sänkyyn in the illative ("into") case instead of the inessive ("in") case?