Breakdown of Oddałem ten prywatny list swojemu współlokatorowi.
ten
this (m)
list
letter
swój
one's own
oddać
to give back / to cast (a vote)
Questions & Answers about Oddałem ten prywatny list swojemu współlokatorowi.
Why is the word swojemu used here instead of mojemu?
You could actually use mojemu here, but swojemu is the reflexive possessive pronoun, meaning one's own. Whenever the owner of the noun is also the subject doing the action (in this case, I), Polish strongly prefers using a form of swój. Because it is your own flatmate, swój is the most natural choice.
What case is swojemu in, and why does it end in -emu?
It is in the dative case. The verb oddać (to give back) requires the dative case for the recipient of the action (the flatmate). The pronoun swój declines just like an adjective. For masculine and neuter words in the dative case, adjectives and possessive pronouns take the -emu ending, matching the dative noun współlokatorowi.
Why doesn't the direct object ten prywatny list change its spelling if it is receiving the action?
It actually is in the accusative case! However, list is a masculine inanimate noun (an object, not a person or animal). In Polish, the accusative form for masculine inanimate nouns looks exactly the same as the nominative (dictionary) form. Therefore, ten prywatny list does not get a new ending.
How does the prefix od- in oddałem affect the verb's meaning?