'Turn' has a different sense in 'turn down the radio' and 'turn the radio around'. And "Down the radio, the girl turned." wouldn't even be accepted by Yoda. 'Down the alley, the lorry turned' is a different matter.

The girl turned down the radio. What happened to phrasal verbs using prepositions? The boy turned up the music in his room. The boy turned up late for this class. The beds were turned down for the night. Your friends are giving you poor advice. :) I would stay away from constituency until you have tuned up your understanding of phrasal verbs.

He turned down the radio is a "tolerable", but "awkward" alternative to He turned the radio down (to turn down = reduce is a phrasal verb). But you can't move the object to between the verb and the preposition in He turned down the road - He turned the road down isn't valid (in that context, down the road is an adverbial element attached to the non-phrasal verb turn).

@FumbleFingers That is not true: Turn down the radio or turn the radio down. You are just confusing the poor lad.

@Han. No; "down the radio" is not a constituent, "The radio" is direct object of "turned" and "down" is a particle, a complement of "turned". It is a 'verb-particle-object' construction.

In "I gave him fifty dollars," you can substitute "him fifty dollars" with just "fifty dollars" and get a grammatically correct sentence. So, is "him fifty dollars" a constituent?

@Lambie: There's a US/UK usage split that I wasn't aware of before. Per this chart, turned the TV down is now (slightly) more common in BrE than turned the TV down. But as this chart shows, the preference in AmE is very different.

...but that's hardly important anyway. My primary point was that you can put the object in either position when it's a "phrasal verb", but you can't do that if you're just turning down a side road (to "turn a side road down" is nonsense). It's essential that learners understand this distinction.

@FumbleFingers Yes, there is a general difference which doesn't mean one never sees the plural in AmE. You won't get this from googling. It comes from listening, in my case, to the news broadcasts such as the BBC versus, say, CNN or ABC news. Or even to British television shows versus American ones (or movies).

If the OP gets the phrasal verb point, that is the main point. What you are doing is extending the point which is not really relevant at this point. Too much, too soon. If you read my examples, you will see they are clear. This person is a learner, so all those explanations will be over his head. Let's leave adjectivals and adverbials for another lesson. This should be on ELL, anyway. You gotta walk before you can run...

@FumbleFingers I agree with some of what you say. Yes, the particle can be positioned between the verb and its NP direct object or it can follow it. The fact that "turn down" is an idiom does not affect the grammar, which in this case is a 'verb-particle-object' construction. Syntactically, the verb phrase "turn down the radio" consists of three constituents ("turn + down + the radio") not two ("turn down + the radio).

@Lambie: You don't like to give an inch, do you? It's obvious from the way OP has isolated "down the radio" as a "syntactic component" that he doesn't understand the relevant syntactic constraints concerning phrasal verbs. Whatever - I'm not trying to teach you anything!

@BillJ: At one level, "turn down the radio" consists of three constituents: "turn + down + the radio" is "valid". But "turn" + "down" are two very closely connected elements that in many ways function collectively the same as single-word verbs such as mute, silence, muffle,... It's possible to put an object between the verb and the preposition if and only if those two words have that special "tight connection". Which is obvious and natural to us as native Anglophones, but it may be counter-intuitive to nns that you can only "break" the pair when they are a pair!

@FumbleFingers Right, and he probably didn't even know of the existence of such a thing as a phrasal verb. I'm not trying to teach you either. I am just giving my opinion that whatever you and BillJ are saying is way over the top for this question. You guys always jump in with the hypher-technical before testing the waters. I believe in providing an answer an OP can understand.

Sounds like this: ling.upenn.edu/~beatrice/syntax-textbook/…. And give me strength: "Another diagnostic for constituenthood"...

@FumbleFingers Yes, as I said"turn+down" is an idiom, but in this case the lexical and syntactic units do not match up. But it's not a matter of "putting an object verb between the verb and the preposition, but of putting a prepositional particle between the verb and its direct object. It's important to understand that "turn down" is not a single word, not a constituent at word level. It's just "turn" that is the verb: this is the the word that takes the verbal inflections, so we have "turned down the radio" but not *"turn downed the radio".

Noting that the imperative and stipulation in "Determine ... by using any of the following tests: substitution and movement" is a hallmark of homework. Just saying.

@YosefBaskin: I'm sure you're right. Personally, I've no idea what "the substitution test" means here, but I rather suspect the OP has no idea that although "the radio" and "it" might appear to be equivalent as references to "the object being turned down", they certainly aren't interchangeable with "The radio is too loud - please turn it down". Where "It's too loud - please turn down the radio", is of course also fine.

"turn downed" the radio is not grammatical. The radio was turned down. The bed was turn downed, maybe.

Of course it's not grammatical. Can't you read?

@FumbleFingers The term 'phrasal verb' is misleading. It is not the whole expression "turn down" that is a verb but just the lexeme "turn". And, as I said, the lexical and syntactic units don't always match up, as is the case in the OP's example.