Breakdown of Ona powinna segregować śmieci.
ona
she / it (f)
powinien
should, ought to
segregować
to sort
śmieć
garbage
Questions & Answers about Ona powinna segregować śmieci.
Why is the word for "should" powinna instead of powinien?
Why doesn't the verb segregować change its ending to match Ona?
Because it follows powinna. Just like in English where we say "she should sort" (not "she should sorts"), Polish requires the second verb to stay in the infinitive (the dictionary form) when it is paired with any form of powinien.
Why do we use the imperfective verb segregować here?
Sorting garbage is a habitual, ongoing responsibility rather than a one-time action that gets completely finished forever. Polish uses imperfective verbs for habits, routines, and general rules.
What case is śmieci in this sentence?
It is in the accusative case, because it is the direct object of the verb segregować (she is sorting what?). For this particular plural noun, the accusative form śmieci happens to look exactly the same as its nominative (dictionary) plural form.