Learn Hardcore Polish: Oni znów czekają na pociąg. - They are waiting for the train again.

In Polish the verb ending already shows the subject: czekają is 3rd person plural, so you know “they.” We include Oni for emphasis, contrast (e.g. “they, not someone else”), or clarity if context is unclear. Dropping it is perfectly fine in casual speech.

What’s the difference between znów and znowu? When should I use each?

Both mean again or once more and are interchangeable in most contexts.
– znów is slightly more formal or written.
– znowu is more colloquial.
Word order and emphasis can be identical: Oni znów czekają… vs Oni znowu czekają….

Why is pociąg in the accusative case here? It looks like the nominative.

The verb czekać (to wait) requires the preposition na + the accusative case to mean “wait for.”
pociąg is a masculine inanimate noun whose accusative singular form is identical to its nominative: pociąg. You know it’s accusative because of the preposition na.

Why do we say czekają na pociąg instead of czekają pociąg?

czekać needs a preposition to link it with what you’re waiting for. To express “waiting for X,” always use czekać na X. Omitting na would be ungrammatical.

How is czekają formed? Which tense and person is that?

czekają is the present tense, 3rd person plural form of the imperfective verb czekać.
Root: czeka-, ending: -ją for “they.” It literally means “they are waiting” (not “they will wait” or “they waited”).

Where does the stress fall in czekają and pociąg?

Polish generally stresses the penultimate (next‐to‐last) syllable.
– cze-KA-ją (stress on KA)
– PO-ciąg (two‐syllable words stress the first)

Could I move znów to a different position? For example, Oni czekają znów na pociąg?

Yes. Polish word order is flexible:
– Oni znów czekają na pociąg. (focus on the fact they’re doing it again)
– Oni czekają znów na pociąg. (slightly more neutral)
– Oni czekają na pociąg znowu. (emphasis on again at the end)
All are correct, just shift emphasis.

Is there a perfective verb for “to wait”? Why don’t we ever say poczekają here?

Perfective doczekać/poczekać means “to wait until (something happens) to completion,” not just “to spend time waiting.” If you said Oni poczekają na pociąg, it would be future tense: “They will wait for the train,” not “They are waiting again.” To keep the ongoing meaning you need the imperfective czekać.