Is a glass of warm milk a grammatical error?

Not to me. I think they are two different statements.

A glass of warm milk means a glass with warm milk in it.

A warm glass of milk means there is a glass, that is warm, with milk in it.

A glass of warm milk is correct. “Warm milk” is the subject of the sentence, the idea you want to convey, what the sentence is about, not “a warm glass.” Some of the grammarians around here may be better at explaining the technicalities and formalities of grammar, usage and syntax than I am and maybe one of them will weigh in.

Neither version contains a grammatical error. If you have a quarrel with one expression or the other, it isn’t on grammatical grounds. In both cases you have a noun modified by an adjective (perfectly correct) and a prepositional phrase with a noun as object of the preposition (also perfectly correct), In the first case, the adjective goes with noun 2, and in the second it goes with noun 1.

“A nose of happy ocean” and “a happy nose of ocean” are also grammatically correct for the same reason, even though semantically they don’t make any sense.

“A glass of warm milk” is precise.

“A warm glass of milk” is informal, commonly used, and understandable.

Yes, I agree with you. And thank you all for the answers.
One of my grammar teachers said the former is wrong.
So I posted my question.
My mother tongue is not English.
Thanks, anyway.

More direct would be warmed milk in a glass but we yanks are lazy…..

Warmed would imply the action in the past, or passive. It might just be a warm day, and the glass is warm. A warm glass of milk. It also implies a glass of warm milk – no-one would actually think someone warmed the glass – then poured cold milk into it. WTF?

I recall someone asking what a pre-heated oven meant for baking.

I’ll have a chocolate milk.
I’ll have a warm milk.

Had to think about it but I think they’re fine.

Neither a glass of warm milk nor a warm glass of milk is a grammatical error, but a culinary one. Ice cream is way better than either – and just as warming, actually.

As LillyCoyote and Jeruba explained, neither is grammatically incorrect; however, “…a glass of warm milk” is the most accurate. “…a warm glass of milk” is an example of a misplaced modifier. Another example of misplaced modifier: “Shelly filed her nails on the sidewalk.” Although we know what the speaker means by the statement, if taken exactly as written, Shelly is a bit unconventional (or, perhaps, desperate) and is using the sidewalk as a nail file. “Shelly filed her nails while on the sidewalk.”

A cold bottle of beer is the same way. It might be the cold beer you’re after, but chances are, if the milk is warm or the beer is cold, the container will be of a similar temperature.

@JamesLynnJohnson, welcome to Fluther!

They are both grammatically correct, and in informal speech both express the same meaning and both will be understood (probably the second is more common?). However, in very precise terms there is a slight difference on what is exactly warm here.

Glass and milk are both nouns. Warm is the adjective here.

An adjective modifies a noun. In this case, the adjective is descriptive indicating a quality (temperature). Adjectives usually are placed before the noun they modify, or are placed after the noun joined by a linking verb (to be). The position of the adjective (syntax) in the phrase will tell you what noun is being modified.

A glass of warm milk = the milk is warm.
A warm glass of milk = the glass is warm (probably the milk too).
Also, a warm glass of milk = the glass of milk is a noun phrase being modified by the adjective warm.

Other semantic considerations come into play here, for when you put a cold liquid inside a warm container the liquid warms up as well and vice versa —this probably accounts for the phrase to mean the same in general terms.

It doesn’t make much difference in informal speech, but say you are using similar phrases for an experiment in a lab; then, temperature is an issue of utmost importance and what is warm —the container or the liquid— could change the outcome of the experiment. The difference in temperature between the container and the liquid can also affect texture or volume in cooking.

(There is no subject or object here because this is not a sentence but a phrase. For the same reason, there is no prepositional phrase as object here [despite the word of in the noun phrase].)

@Porifera, I think you must be responding to me when you say “there is no prepositional phrase as object here” because nobody else mentioned a prepositional phrase. But that was not my comment. I said “a prepositional phrase with a noun as object of the preposition.” The prepositional phrase is “of [warm] milk.” The preposition is “of.” “Milk” is the noun that is the object of the preposition. There was no mention of a “prepositional phrase as object.” That wouldn’t make any sense.

In using the expression “a warm glass of milk” (“a cold mug of beer,” “a nice cup of tea”), we tend to see the beverage and its container as a unit. So in everyday use we put the adjective in front of the whole noun phrase. Conceptually “warm” modifies the whole thing (and in reality if one or the other is warm, they will soon both have the same temperature), and that makes more intuitive sense to us than a logical analysis.

@Jeruba I was not responding to you, I am now. When I respond directly to one person, I usually write their name. I was responding to the person that posted the question.

But that was not my comment…That wouldn’t make any sense. Precisely because that was not your comment, I wasn’t responding to you.

The logical analysis is appropriate because this is a grammar question and the OP’s teacher said the second phrase was incorrect, so a structural explanation was called for. As a teacher myself, I require my students to explain to me in detail when they disagree with me, or when they think I’m wrong. If my students tell me that one sentence is correct just because everybody uses it like that, or because it sounds good, or for intuitive reasons, more often than not I will not accept their answer. I usually want them to explain to me in grammatical, lexical, semantic, or even pragmatic terms, so that I know they really know what they are talking about.

Well, then, @Porifera, no one spoke of a “prepositional phrase as object” until you brought it up, so I didn’t see what it was you were countering.

I am all for careful analysis. In fact, I’ve been known to go in for it myself. But that’s not what’s going on—i.e., we’re not making the precise distinction implied—when we choose the expression “a warm glass of milk” over “a glass of warm milk.” That’s my point. I am also saying, just as you are, that the difference is not a matter of grammar because they are both grammatically correct.

@Jeruba I am not for confrontation in such a limited medium as this one. Lengthy explanations are time consuming, people are focusing on different angles, etc. It seems you felt attacked somehow and I wonder why.

I am all for careful analysis. However, you have suggested/mentioned the intuitive approach as the best explanation for this matter.

But that’s not what’s going on—i.e., we’re not making the precise distinction implied—when we choose the expression “a warm glass of milk” over “a glass of warm milk.” Then, what are we doing here? It isn’t fair to just say this or that is or isn’t grammatically correct, a little bit of elaboration is required to see things clearly, specially when the OP didn’t seem to have a clue by the way he worded his question. I gave a detailed grammatical explanation and added a bit of semantic analysis. I don’t see that being off topic.

That’s my point. I am also saying, just as you are, that the difference is not a matter of grammar because they are both grammatically correct. I noticed that from your post before the last, and was wondering why you even felt the need to rebut if we were saying the same thing.

@Porifera, I don’t feel attacked or feel a need to rebut. And I am not familiar enough with your patterns to know in advance that you always use direct address when responding to someone; many don’t. So I did think you were addressing me because I was the only one who had said anything about prepositions and objects, and your response sounded like a rebuttal to something I didn’t say, so I just wanted to clear that up.

I am drawing a distinction between everyday use of the expression (But that’s not what’s going on—i.e., we’re not making the precise distinction implied—when we choose the expression “a warm glass of milk” over “a glass of warm milk.) and the process of analysis. When we choose the expression—i.e., in conversational speech, when I invite you thus: “Here, have a nice warm glass of milk and you’ll sleep better”—we are not performing the analysis or making scientific distinctions between a warm glass and warm milk. We’re just employing a common and entirely understandable locution. That’s not an appeal to intuition over analysis; in matters of grammar I favor analysis. That’s just a statement that the two forms of the expression are used interchangeably in common practice and that there’s really no reason to do otherwise.

This sort of forum is just fine for exacting analyses and debating of fine points, and we do it around here all the time. Your skills seem well suited to that aspect of fluther life. I like to think we can usually engage in it without a sense of confrontation, although it seems to be true that nothing can arouse the passions like a question of English grammar.

But in responding to this particular question, there is no issue of grammatical correctness at all, as we have agreed. (“Colorless green ideas sleep furiously.”) I mentioned that again only to bring us back to the issue raised by the OP, who had—as is often the case—been given incorrect information by his or her grammar teacher.

@Jeruba It takes more than a grammar question in any language to ignite or arise my passions. Your direct response to me forced me to respond to your comments, not out of passion or need to rebut, but out of courtesy. I do like to engage in a civil debate when I have a counter position to argue against, but not in situations like this, where we have been practically saying the same thing with different words all along.

If it started out cold, then it got warm or less cold, why not just say a glass with warmed milk. because that is technically what it really is.

@Hypocrisy_Central well, my dear, that too leads to differences. The use of warmed instead of warm. Warmed emphasizes the fact that the milk has been warmed by some warming process (heat, reheat) and warm alone just indicates the condition (temperature) of the milk at the moment of speaking. The never ending story… :)

@Hypocrisy_Central – if milk comes out of the cow at cow-temperature and is rapidly cooled down to retard spoilage, wouldn’t it be re-warmed milk? ;)