Breakdown of Nie powinniście wyrzucać śmieci w lesie.
nie
no / not
w
in / on (a day)
las
forest
powinien
should, ought to
Questions & Answers about Nie powinniście wyrzucać śmieci w lesie.
Why is it powinniście and not just powinni or powinieneś?
The word powinniście is the "you all" (plural) form of powinien used for a group that includes at least one male. It combines powinni (the masculine personal plural form) with -ście (the ending for "you" plural). If you were speaking to just one man, it would be powinieneś.
Does powinniście need to be followed by a specific verb form?
Yes, just like "should" in English, forms of powinien act as helper verbs. They are always followed by a verb in its dictionary form (the infinitive). Here, that infinitive is wyrzucać (to throw away).
Why use the imperfective verb wyrzucać here instead of the perfective form wyrzucić?
The imperfective wyrzucać is used because this sentence is expressing a general rule (you should never throw garbage in the forest). If you were giving advice about one specific, completed action (like throwing away a single wrapper right now), you would use the perfective form.
Because the sentence is negative, does the word śmieci (garbage) change its case?
Yes, but you can't see the change! Normally, adding Nie before the verb forces the direct object to change into the Genitive case. However, for the plural word śmieci, both its standard object form (Accusative) and its negative object form (Genitive) are spelled exactly the same.