compound adjective or phrase?

Question

I know some phrases can make up compound adjectives. But how can I tell if it is an adjective or not? Examples:

1. 1. I threw away the worn-out socks. (compound adjective)
   2. I put the socks worn out on the table. (participle phrase)
   3. These socks are worn out. (here, I have no idea...)
   4. Something worn out deserve to be thrown away. (not sure...)
2. 1. Doctors have evaluated the health of a given at-risk population. (compound adjective)
   2. Police took away the children at risk. (preposition phrase)
   3. These people are at risk. We should help anybody at risk. (Here, I have no idea...)

Answer 1

I put the socks worn out on the table

Remember in English an adjective generally comes before the noun, otherwise it can be confusing -- particularly in this case since "worn" is both a verb and an adjective. This sentence isn't grammatically correct, but it might be fine in some styles of colloquial English so I'd parse it to mean, "I put the socks (that someone wore) out on the table," and not, "I put the worn-out socks on the table."

The overarching rule is that an adjective (or adjective structure) modifies a noun. So, in your first sentences, since you intend "worn-out" to modify "socks", all the examples are adjectives of one sort or another. In the second example, "at-risk" modifies "population", "children", etc. so it's also an adjective.

Of course you can have longer examples of compound adjectives. In the "Harry Potter" books and movies various characters famously call Voldemort "He-who-must-not-be-named". Here the entire phrase acts as a kind of proper noun, but internally "who-must-not-be-named" modifies "He" and so functions as an adjective (and would probably be classified as an "adjective clause").

Answer 2

In section 1, worn out is a participial phrase, which functions exactly like an adjective. We can also call it a compound adjective. When we use something as an adjective and place it before the noun that it applies to, we hyphenate it. Example 1 gets a hyphen because worn out appears before the noun that it qualifies: the other examples don't, but they are still both participial phrases and compound adjectives.

Sentence 1.2 is not grammatically correct. Furthermore, it is impossible to tell what you meant. Are you using a phrasal verb put out, or are you trying to use worn out as a participial phrase?

As a phrasal verb, it should be

I put out the worn socks on the table.
I put the worn socks out on the table.

As a participial phrese, you have options for where to put the participial phrase:

Worn out, I put the socks on the table - worn out applies to me.
I put the worn-out socks on the table - worn out applies to socks.
I put the socks, worn out, on the table - worn out applies to socks.
I put the socks out on the table, worn out - worn out applies to socks.

Moving on to part two: at risk can work as a compound adjective or as a prepositional phrase: in some contexts, it could be either.

A prespositional phrase can qualifies a noun like an adjective does, but it must go after the noun that it qualifies, unlike an adjective which goes before the noun that it qualifies: note that there are exceptions for some pronouns.

In the first example, at-risk is a compound adjective: in this position, it requires a hyphen.

In the second example, at risk goes after the noun that it modifies. This is a prepositional phrase: it functions like an adjective, but it goes after the noun that it modifies. You know it's not a real adjective because you couldn't use good in this position.

In the third example, the first instance of at risk follows a verb so it can only be an adjective which describes people. The second instance could be either a prepositional pharase or an adjective qualifying anybody: you can prove that they can both be adjectives by substitute good in either position. As compound adjectives, neither is used before the noun it qualifies, so no hyphen is required.

Answer 3

1. a) I threw away the worn-out socks.
   b) I put the socks worn out on the table. [INCORRECT]
   c) These socks are worn out.
   d) Something worn out deserve to be thrown away.

Before writing my answer about "worn out", let me tell something about the sentence 1.b) and 1.d). Sentence 1.b) is not a correct sentence, whereas sentence 1.d) is correct.

A pronoun like something can be post-modified by an Adjective Phrase (AdjP), here worn out. But in sentence 1.b) the noun - socks - can not be post modified like this way. [For further reference turn to page no. 1293 sec 17.56 of Quirk et al.]

So for discussion, I will exclude the incorrect sentence 1.b).

In all the sentences above, "worn out' is adjectival, and not verbal.

We will examine them one by one -

I threw away the worn-out socks.

Here we need to concentrate on the Noun Phrase (NP) - the worn-out socks. The bold part in that phrase is a modifier of the noun - socks. But what word class it is in?
Generally speaking, it is best to test such cases to alter its position. Let's alter its position:

I threw away the socks that was worn-out.

Now replace the copular verb - was - with other copular verbs, like seem or become. It is still grammatical, and hence worn-out is not verbal, instead it is adjectival.

These socks are worn-out.

Here the same way, we can judge that worn-out here too is adjectival. Just replace are with seem or become.

Something worn-out deserve to be thrown out.

Here the pronoun something is being post modified by an adjective worn-out. We can also re-write this sentence this way -

Something (that are) worn-out deserve to be thrown out.

Here like the previous case, replace are with seem or become. And hence it is Adjectival, and not verbal.

In all the above cases, worn-out is adjectival. And it is formed by the past participle form of the verb wear and a preposition out. It has two lexical bases. And it can be considered as a Compound Adjective. [Reference - Page No. 535 of Biber et al.]

Answer 4

I agree with the other commenters but will offer my own view as well.

I threw away the worn-out socks. (compound adjective)

Here 'worn-out' is an adjective modifying the noun socks

I put the socks worn out on the table. (participle phrase)

I agree with the other commenter who said this is an awkward construction. Perhaps you could say: I put the socks, worn-out, on the table. (or) I put the socks (worn-out) on the table. (Like an afterthought an incidental description.

These socks are worn out. (here, I have no idea...)

In this example, it is still an adjective, though typically you would hyphenate it.

Something worn out deserve to be thrown away. (not sure...)

Same here modifies the pronoun: something. I would hyphenate it. Some might argue that 'out' is acting as an adverb modifying the adjective, but I think it needs a hyphen ;)

Doctors have evaluated the health of a given at-risk population. (compound adjective)

I agree here but would consider 'given' to be an adverb.

Police took away the children at risk. (preposition phrase)

I agree that this is a preposition, working as an adjectival.

These people are at risk. We should help anybody at risk. (Here, I have no idea...)

Prepositional phrase working as an adjectival phrase.

Hope it helps some more!