Is this sentence from Andrew Carnegie ambiguous? [duplicate]

Your friend is wrong: the sentence is grammatically completely correct with the meaning you intended. There is no rule that requires the prepositional phrase "in my underpants" to modify the immediately preceding noun phrase "vegan cheese." Not even a "technical" one. It sounds like the kind of pseudo-rule that would be invented by someone under the misimpression that the rules of English syntax are designed to avoid ambiguity. In fact, this sentence, like many others, is just syntactically ambiguous. That's not a problem; many sentences are. Context makes it clear what you mean, in this case as in many others.

Here is a basic summary from "Linguapress.com Essential English Grammar" of where verb phrase modifiers (like the prepositional phrase "in my underpants") can go in an English sentence:

adverb phrases (groups of words, usually formed starting with a preposition) can come in three possible places:

a) Before the subject (Notably with short common adverbs or adverb phrases, or sentence adverbs - see below) [...]
b1) After the object (virtually any adverb or adverb phrase can be placed here) [...]
c) In the middle of the verb group. (Notably with short common adverbs of time or frequency)

The grammatical ambiguity arises from positioning rules like these and from the fact that prepositional phrases can be used to modify either noun phrases or verb phrases.

There was a recent Language Log post mentioning the issue of "prepositional phrase attachment": Annals of parsing

Two of the hardest problems in English-language parsing are prepositional phrase attachment and scope of conjunction. For PP attachment, the problem is to figure out how a phrase-final prepositional phrase relates to the rest of the sentence — the classic example is "I saw a man in the park with a telescope". For conjunction scope, the problem is to figure out just what phrases an instance of and is being used to combine.

The title of a recent article offers some lovely examples of the problems that these ambiguities can cause: Suresh Naidu and Noam Yuchtman, "Back to the future? Lessons on inequality, labour markets, and conflict from the Gilded Age, for the present", VOX 8/23/2016. The second phrase includes three ambiguous prepositions (on, from, and for) and one conjunction (and), and has more syntactically-valid interpretations than you're likely to be able to imagine unless you're familiar with the problems of automatic parsing.

See also section 1.2 "Ubiquitous Ambiguity" in "Analyzing Sentence Structure," a chapter from Natural Language Processing with Python by Steven Bird, Ewan Klein and Edward Loper.

Syntactic ambiguity is common in all natural languages. It's not feasible to avoid it when constructing a sentence in English, and trying to do so in general will provide no benefits to your writing. Obviously, it's a good idea to avoid ambiguous syntax when there is a real chance of confusion, but that's not the case with your sentence. Your friend obviously knew what you intended: he's deliberately misinterpreting your sentence.

Here's a similar sentence from the Declaration of Independence, which I would say is a document written in a formal style:

In every stage of these Oppressions We have Petitioned for Redress in the most humble terms.

This doesn't mean they wanted redress that was in the most humble terms. It means they petitioned in the most humble terms for redress.

It is neither bad grammar nor bad style to use ambiguous grammatical structures.

I was gonna just make this a comment but I had too much to say, because this less pedantry and more "being obnoxious".

"I technically said that the vegan cheese was in my underpants..."

Have him point you to the place in the technical manual where it says that a prepositional phrase must always modify the thing it follows. What if you had left out "at home"?

"I'm eating vegan cheese in my underpants and singing Bushes of Love."

Do you have to move "in my underpants" to the end? But then you're singing into them! Or you move it to the front, and suddenly the CHEESE is singing "Bushes of Love"!

We have four bits of info: "at home", "singing", "eating cheese" and "underpants". You can arrange these in any fashion, and the sentence meaning does not change.

• "I'm in my underpants eating vegan cheese and singing Bushes Of Love at home."
• "I'm singing Bushes Of Love in my underpants and eating vegan cheese at home."
• "I'm at home in my underpants eating vegan cheese and singing Bushes Of Love ."
• "I'm eating vegan cheese and singing Bushes Of Love in my underpants at home."

On this last one, you could be literally singing INTO your underpants, right? Rolled up like a little megaphone or stuffed in your mouth, I dunno. There are a lot of words you could add to the sentence to remove ambiguity but you know what? That's not the way real people talk.

If you wanna get super technical, you could probably map out the meter of those sentences: You might find that you picked an arrangement of words that suited your speaking rhythm better. You might also find, if you cared to scrutinize" that you added "in my underpants singing" at the end because it's funnier that way.

The rule, if there is one, must surely be "Add words to clarify the meaning of your sentence as needed, but no more." This person (and I've met so many of them over the years) seems to think the rule is "Add words until your meaning couldn't possibly be misconstrued by the most fatuous of listeners."

What's more, if you were actually eating cheese out of your underwear, just as if you were singing into them in my other example, that sentence would not adequately convey that. English (as used) is particularly imprecise in this regard: If you are doing something unusual, you very often have to spell it out. This is pretty sensible really.

Nobody would actually think what your friend said. If you had meant that, you'd have to say:

"I'm eating cheese out of my underwear. Yes, you heard me. I've put vegan cheese in my knickers, thinking they would make for a delightful serving tray."

So, pfeh. The point of talking is communication. And the point of drawing people's attention to obviously wrong possible misinterpretations of someone's words—well, that's what we call "politics".

This is classic -

I shot an elephant in my pajamas, how he got into my pajamas, I'll never know.

It's a joke, from 1930's Groucho Marx' film Animal Crackers. "I shot an elephant in my pajamas" is fine as is, as it simply means that Groucho woke up, grabbed a gun and fired. It was he, not the elephant who wore the pajamas. This, and other jokes play off the seeming ambiguity involved, but all of these jokes go back to this style. It's likely that Shakespeare planted a similar one in a play or two, I'm not claiming Marx to be the first.

I can't think of a case where there would be a genuine ambiguity. If the cheese were in the underpants, you'd say, "I'm eating cheese from my underpants". Likewise, you eat ice cream from a bowl, or a candy bar from your pocket. You eat strawberries in your kitchen, or in a submarine.

Could you be eat walnuts in a carrot cake? If you were picking them out and eating them, I'd say that "from" would be more appropriate. If you had a nut allergy, you could show up to the hospital and say "I ate walnuts in a carrot cake", which I suppose is appropriate. But that implies that you also ate the cake. You didn't eat the underpants.

Some sentences have to be understood using semantic knowledge. For instance, "I ate the cheese with a fork" and "I ate the cheese with an olive" are both grammatically correct, and it's up to the listener to figure out the meaning.