What's wrong with this adjective?

OK, in this sentence, the word “on” is an adverb:

I switched the living room light on.

And here, it’s an adjective, according to Merriam-Webster:

The light in the living room is on.

So why does this one sound so awkward?

Please turn off the on light in the living room.

If I replaced “on” with “bright” or “red”, it would sound fine. So, I have a few questions:

  1. Is it actually grammatically incorrect to say “an on light” (referring to one that’s lit), or does it just seem strange because it’s uncommon?

  2. Is there a word to describe adjectives like this, that can be used in “the light is ____” but not “there’s a ____ light”?

  3. Bonus: What other adjectives fall into the same category?

  1. No, it’s not grammatically incorrect.
  2. Don’t know if there are any.
  3. What category? Words that are usually used as prepositions that have incidental uses also as adjectives? Off (as in “off days”), “up” and “down” as in “up and down arrows”), and there are probably a bunch more.

Adjectives that you’d use after “is” but not before a noun. Or am I the only one who does that?

So why does this one sound so awkward?

Please turn off the on light in the living room.
One reason it sounds so awkward (and insulting to the reader) is that it is painfully redundant. If you’re going to turn a light off, it must necessarily be on.

Well that’s true. But not really what the OP is asking, I think. This registers about the same on the awkward scale, and it isn’t redundant:

“Do you see that light over there?”
“Which one? I see two different lights.”
“Oh, sorry. I’m talking about the on light.”

The only question I can answer in the OP is #3. I would say that I am 16, but nobody ever calls me “that 16 kid over there.” We do say “that 16-year-old kid over there,” which is similar to saying, “I am 16 years old.”
16-year-old… 16 years old.
This is crazy.

I think what we’ve got here are “Germanic” verbs. “On”, in the above sentence, is not an adverb, it’s part of a verb that, if English were German, would be “on-switchen”. The light is not now the “on” light, it is the “onswitched” light.

[Henrich Schnibble]Ich schwitche das lebensroom light on. Es ist ongeschwitched, ja? Kannst du das otheren light onswitchen?[/Heinrich Schnibble]

Other examples: I knocked your sister up. She has been upknocked. She is not your “up” sister, she is your upknocked sister.

The director will have the film editor take the unwanted footage out. The footage to which this is done is not “out” footage, it’s “outtakes” footage. (And this is one of the relatively rare examples in English where the infinitive is actually used that way).

All right… that’s not M-W’s interpretation, but I’ll go along with it. How about in this sentence:

The light in the living room is on.

Would you say “is on” is also a multipart verb, “onbeing”?

Maybe not, but turn on is. In this case, “on” is clearly a part of the verb. The fact that they don’t have a separate entry for “switch on” doesn’t mean it’s a different case, just not in common usage enough to warrant an entry.

In the example you mention in this latest example, the answer is “no.” “On” is clearly a subjective complement.

My idiolect, at least, would never permit that construction. It’s a sensible extension of the adjective-like use of it in your earlier examples, so I wouldn’t be surprised if some English dialects made this a productive grammatical tool, but it certainly is ungrammatical for me.

It’s not really an adjective or an adverb; it’s part of a phrasal verb, “to turn on”; it’s a piece of a verb, so it doesn’t work on its own. The German-flavored examples that AHunter3 offers actually sound much more reasonable to my ears (though clearly not possible in standard English.) Verbs like that - and there are hundreds - can’t be analyzed as composites of their parts. Nothing more than perhaps the vaguest sense unites “break in”, “break out”, “break up”, “break down”, “break through”, etc. Or turn: “turn in”, “turn out”, “turn over”, “turn on”, “turn off”, “turn into”, “turn down”, “turn up”. There’s no productivity to these constructions - you can’t create new ones by analogy from other ones - you can’t come up with, for example, “turn through”, and expect others to know what you mean, since these are single, indivisible constructions that just happen to come in separate chunks.

These verbs, incidentally, are the source of a good number of the stranded prepositions that get more gullible English students’ dander up. (See, look, I just did it!) Or, in the (probably apocryphal) words of Chuchill, “That is the kind of pedantry up with which I shall not put!”

Not really trying to hijack, but my favorite cute “story” about ending sentences with prepostions is what the little boy said to his father who had taken a book about Australia up to his room to read to him:

Daddy, why did you bring that book I didn’t want to be read to out of from about Down Under up for?

(And yes I realize “Down Under” is here a noun. It’s still cute.)

There are differences in the way some adjectives can be used (by rule). Surrounding words and context also have an effect, which makes forumlating a concise set of covering rules difficult. Grammatical logic has nothing to do with how the rules of common usage come to be.

Consider two different uses of the adjective “red” (noun phrase in green, verb + predicate in blue):

The light is red.
The red light is there.

In the first sentence above, “red” is the predicate of the verb “is”. In the second sentence, “red” is part of the noun phrase, and not part of the verb’s predicate.

Not all adjectives can be used in both ways in all situations. What uses are allowed can depend heavily upon which other words appear in the sentence:

The light is on.
The on light is there

The switch is on.
The on switch is there.

The ramp is on.
The on ramp is there.

The difference between predicate vs. non-predicate use of adjectives is more marked in some other languages. Russian, for example, has different forms for most all adjectives depending on whether the adjective is a predicate or not.

There are actually two kinds of adjectives: predicative and attributive. Predicative ones have to be used with a copula, and attributive ones have to come before the noun. Most adjectives are both (the room is red, the red room).

A few adjectives are one or the other. For example, you can say “the woman is alone,” but you can’t say “the alone woman.” “Alone” is therefore a predicative adjective. Conversely, you can say “a mere delay,” but you can’t say “the delay was mere.” “Mere” is an attributive adjective.

Apparently, “on” in the sense of “functioning” is only a predicative adjective.

I’ve seen the same sentence before minus the noun; it was something like “What did you bring that book I didn’t want to be read to out of up for?” except I think the version cited had six prepositions at the end. The interesting part was (this was an old Language Log posting I’m not gonna search for) most of the prepositions couldn’t be moved; it may be a clumsy sentence, but the ONLY grammatical form had six prepositions at the end of the sentence. Goes to show the silliness of the old rule.

Excellent. A quick web search turned up this and this, which distinguish between attributive and predicative adjective positions, and give more examples of adjectives that can only be used in certain positions.

“Afraid” is on the list, and the first link mentions that many of the predicative-only adjectives start with “a”. I wonder if there’s a historical reason for that, and if it’s related to forms of hillbilly syntax (for lack of a better term) like “Froggy went a-courtin’”.

“On” in “The light is on” strikes me as adverbial – implying “has been switched on.”

If you choose to construe it as an adjective, its use is as a disjunctive adjective – one appearing in the predicate which modifies the subject of the sentence or clause. Most English adjectives can function equally well in prenominal or disjunctive setting: “The red light” vs. “The light is red.” But a few, particularly the possessive-pronoun adjectives, vary according to their position: “It’s our light” vs. “That light is ours.”

Apropos of this whole thing, remember Wendy Carlos’s album Switched-on Bach, in which she performs Bach keyboard pieces on the Moog synthesizer. “On” here can be construed as either an adverb modifying the participle “switched” use adjectivally, or, more accurately, as part of a compound participial adjective “switched-on.”