Breakdown of Pod wieczór zaczyna się ściemniać.
zaczynać
to start (imperfective)
wieczór
evening (noun)
pod
towards / approaching (+ Accusative)
ściemniać się
to get dark
Questions & Answers about Pod wieczór zaczyna się ściemniać.
Why is pod used here, and what case is wieczór?
In this context, the preposition pod combined with the Accusative case is used for temporal approximation. It means 'towards', 'approaching', or 'just before' a certain time. The word wieczór is in the Accusative case, which looks identical to its Nominative form here because it is an inanimate masculine noun.
Which verb does the się actually belong to in this sentence?
It belongs to ściemniać. The reflexive verb for 'to get dark' is ściemniać się. While zaczynać się (to start) also exists, here zaczyna is just the active 'starts' followed by an infinitive. The się naturally floats between the two verbs, which is its most common position in sentences with an infinitive.
What happens if I forget the się and just say zaczyna ściemniać?
It completely changes the meaning! Without się, ściemniać is a transitive verb meaning to darken something (like dimming a screen). Even more importantly, in everyday colloquial Polish, ściemniać is a very common slang word for 'to lie', 'to bluff', or 'to talk nonsense'. Without the się, native speakers might think someone is starting to lie!
Why is there no Polish equivalent of the word 'it' in this sentence?