"Ask a policeman!"
Translation:Chieda a un poliziotto!
Well, "(Lei) Chieda a un poliziotto!" is formal. "(Tu) Domanda a un poliziotto!" is informal, apart from that there is no difference in the meaning of the phrase.
Collins makes a distinction between asking someone for something (information) and asking someone to do something. The latter requires "a" but the former does not. Is this standard dictionary wrong? Is actual usage different?
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?
That is very interesting. So, by that definition:
chiedi a un poliziotto = ask (someone) for a policeman
chiedi un poliziotto = ask a policeman (something)
Is my understanding of what Collins says correct?
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.