"Ask a policeman!"
Translation:Chieda a un poliziotto!
I didn't state that very well. Sorry. It's actually the reverse of how I seem to have misled you. Chiedere is normally a transitive verb; it needs a direct object:
chiedi indicazioni = ask for directions (from some unspecified person)
chiedi aiuto a un poliziotto = ask a policeman for help
chiedi a un poliziotto di aiutare = ask a policeman to help
chiedi di un poliziotto = ask for (ask to see or talk to) a policeman (Collins labels this as intransitive - no direct object)
In Duo's sentence the direct object is also missing; the "a" marks "un poliziotto" as the indirect object:
chiedi a un poliziotto = ask a policeman (for something, or to do something, unknown)
That looks ungrammatical, but in the imperative and colloquially, it looks possible. It would be helpful to have a native speaker's reaction.
Another form I'm not sure of is "Chiedi un poliziotto" =? ask for (demand) a policeman. It looks grammatical, but it makes a person into the thing being asked for - not sure that works. Again, native assistance è chiesto.
I'm not a native, but I agree in that I don't think "Chiedi un poliziotto" would work, as you're treating 'poliziotto' as something that can be asked by someone such as a 'question' or 'directions'.
If you want to ask for a policeman without using a preposition, in the same way as an answer to a question, then you'd probably use richiedere: "richiedi una risposta", "richiedi un pagamento", "richiedi un poliziotto"...?
Interesting ploy. But it still doesn't answer the basic problem. "Richiedere" means "request, demand, or ask again," just a bit more insistent than "chiedere." I think maybe one would "chiedere (o richiedere) l'aiuto (o la presenza) a un poliziotto." If there's an easier way to say that I'd be grateful to know it.
"(Ri)chiedi un poliziotto" doesn't make sense. You are treating an human being like an object.
"chiedi a un poliziotto = ask a policeman (for something, or to do something, unknown)"
This is fine, nothing wrong here.
Where's the church? I don't know, ask a policeman (for directions) Dov'è la chiesa? Non lo so, chiedi (la direzione) a un poliziotto.
Thanks for the clarification - but is there a good way to ask for a policeman? Like, if you call 112, and ask for a policeman, you want the operator to metaphorically 'give' you a policeman to speak to. At least, it can be expressed this way in English - is it possible to in Italian?
No. Italian and English constructions are different.
Chiedere qualcosa (d.obj) a qualcuno (ind.obj)
Literally: ask something to someone
In English, the direct and objects are inverted, since the object is not the thing, but the person you ask.
Chiedere (qualcosa) a un poliziotto = ask a policeman (for something)
Chiedere un poliziotto = ask for a policeman. Like "take me a policeman", it's odd.