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Comment by Xophmeister | Hacker News Reader

A similar phenomenon, at least in English, is that you can (technically) infinitely embed subclauses without using complementisers ("that", "who" and "which"). So you get unparsable things like:

   The dog the cat the mouse feared loathed barked.

...punctuated and complementised makes it slightly better:

   The dog, who the cat, who the mouse feared, loathed, barked.

...unwound makes it readable, but changes the semantics subtly but significantly:

   The mouse feared the cat, who loathed the dog who barked.

I say "technically" because there's nothing stopping you from doing this, but in reality, even one level of embedding can be borderline nonsensical (e.g., the "The horse raced past the barn fell" example).

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The ad absurdim example of this phenomenon is the Buffalo buffalo sentence: https://en.m.wikipedia.org/wiki/Buffalo_buffalo_Buffalo_buff...

Here's a toy Python parser I wrote many years ago actually listing out all valid parses of this sentence: https://github.com/taliesinb/chartreuse/blob/master/README.m...

Steven Pinker has a nice one of these:

  The rapidity that the motion that the wing that the hummingbird has has has is remarkable.

    The dog, who was loathed by the cat whom the mouse feared, barked.

Unwound and same meaning as your first and second sentences.

Or even simpler:

    The dog, who was loathed by the cat who was feared by the rat, barked.

Come to think of it, this reminds me somewhat of tail-recursion optimization.

You can't "technically" do that. Which "rule" (from which rulebook) do you think allows you to arbitrarily repeat structures?

This is called center embedding, and it's actually the subject of quite a lot of research. Some of this research has led to a distinction between grammatical (which a sentence like "The cat the rat the dog bit chased escaped" may be) and acceptable (which such a sentence is not). Other research has deemed it agrammatical and unacceptable.

Here's a helpful presentation summarizing some of this research: https://depts.washington.edu/lingconf/slides/Bader&Haeussler...

The sentence the comment the user replied to included parsed with difficulty.

There's no rulebook when it comes to syntax (grammar), unless you're a prescriptivist. There is plenty of precedent for embedding subclauses (e.g., "Here is a sentence, that I just made up, which has an embedded subclause."), but -- beyond anecdotal data -- there is no hard cut-off point to how many times you are permitted to embed. Empirically, most people don't like more than one level, but plenty of people allow it; thus it becomes more a function of cerebral load than it does an argument of permitted structures.

If you're arguing over technicalities, you are inherently adopting a prescriptivist approach.

There are two possible approaches to your sentence and neither renders it grammatically correct. A prescriptivist would dismiss it as not being allowed by any rules while a descriptivist would point out that it defies both common usage and intelligibility.

I disagree, and FWIW, I find your tone hostile.

A prescriptivist would say it follows allowed grammar rules but is still unintelligible.

A descriptivist would say it follows common usage patterns but takes it to such an extreme as to be unintelligible.

You see this pattern more often with proper names:

- That's the house Jack built.

- That's the woman the house Jack built fell on.

- That's the lawyer the woman the house Jack built fell on hired.

- That's the briefcase the lawyer the woman the house Jack built fell on hired carried.

At what point does it become "incorrect"? When it becomes unintelligible to most native speakers?

It's also worth noting these sentences seem much stranger in writing than they do when heard. In writing, most sane people will use punctuation in the examples above. But in speaking, our tone of voice conveys enough context to use more streamlined structures.

> At what point does it become "incorrect"? When it becomes unintelligible to most native speakers?

Beyond 1 level of nesting. There's no rule allowing arbitrary nesting, nor do people commonly nest beyond 1 level.

I'm not sure where you saw hostility in my comment.

By and large, the rules I learned in various English and grammar classes, beyond the initial sentence structure, were prohibitive rather than permissive; there's no rule explicitly _allowing_ arbitrary nesting, because why would need a rule to specify that, but there's also no rule that I'm aware of that _prohibits_ arbitrary nesting.

In fact, the "rule" that matters here is general sentence structure. It's fine to embed a single secondary clause inside a primary clause:

  That's the woman [the house Jack built] fell on.

The structure of the inner clause has no further restrictions on it than the structure of the outer clause. Thus, the entire above sentence is perfectly valid as an inner clause to a new outer clause:

   That's the lawyer [the woman <the house Jack built> fell on] hired.

There's nothing in any grammar book that I'm aware of explicitly prohibiting infinite nesting of this sort; it's just silly and quickly becomes unintelligible. Though I definitely take Tenhundfeld's point that this sort of structure is a lot more common in spoken language, and in fact it's a lot more easily comprehensible with the aid of vocal cues and tones.

Can you point me to the rule disallowing arbitrary nesting? I'm not aware of a rule existing in either direction, besides vague guidelines to write clearly.

Also, which example is 1 level of nesting? I think "That's the woman the house Jack built fell on." is 2 levels nesting, and I frequently hear constructs like that – in speaking. I agree it's rarer in writing though.

For example: What server is that? That's the server the consultant Jack brought in set up.

I'd never write that, because it's confusing. But I will naturally say things like that, without any problem in clarity, because you have more granular control over grouping and pausing, etc. If I said a sentence like that, you might hear it more as "That's the server the-consultant-Jack-brought-in set up."

Anyway, sorry if I misread your tone. It just came across very much as "I know what's right, and you're wrong." That might have been me projecting though. :)

There's empirical work on this [1] (alas, paywalled): multiple center embedding in speech is rare but exists. It is more common in writing.

There are examples of 2 levels of center-embedding which are clearly grammatical and not hard to understand:

> Anyone [who saw the woman [who committed the crime] at any point] should be questioned.

Others are very hard to understand:

> Anyone [who the man [who the woman shot] killed] should be questioned.

There are many factors that make a sentence hard to understand, not just degree of embedding. Some degree 2 sentences can be easy, and some degree 1 sentences can be hard (e.g. "the horse [raced past the barn] fell", which has only 1 level of embedding).

So if you want to describe English with the rule "no embedding beyond 1 level" then you're going to miss a lot of valid sentences while also failing to rule out lots of invalid ones.

Contrast this with a valid descriptive rule of English, such as "determiners such as 'the' always come before the nouns they modify". I can say "the man died", but "man the died" is never comprehensible under any circumstances and cannot be made better.

No one would say that a sentence with 10 levels of embedding is perfectly fine English. But descriptively, you have the problem that there is no non-arbitrary upper bound on embedding degree: it's not clear when one more level of embedding takes you from grammatical to ungrammatical, and furthermore it depends on the contents of the embedded clauses.

There is also some work I'm aware of, currently in prep for publication, showing that the extent to which people can understand multiply-embedded sentences strongly correlates with IQ (measured by Raven's matrices).

All this suggests that the simplest descriptive rule is to say that English allows center-embedding recursively, but that there are human processing limitations on sentences that create very deep stacks. The "human processing limitations" part is basically the whole field of psycholinguistics: many details have been worked out, but many details are still sketchy.

[1] Karlsson (2007): http://journals.cambridge.org/action/displayAbstract?fromPag...

Thanks for sharing the research, it's fascinating that there has actually been serious investigation of this.

That being said, I still think the rule of 1 level still makes sense (not that all 1 level embeds are valid or easy, but that all embeds beyond 1 level are invalid).

> Anyone [who saw [the woman who committed the crime] at any point] should be questioned.

That sentence has two complementisers, which the OP's sentence specifically did not. Introducing complementisers completely changes the rules and I think makes embedding much more possible.

> Anyone [who the man [who the woman shot] killed] should be questioned.

Even with the brackets, I don't understand this one. Anyone killed by the man should be questioned?

(Also, shouldn't they both be 'whom'?)

Saying it stops at level 1 implies the valid rule of embedding is a special case itself of an invalid general rule, rather than it being a general rule itself. If the special case is the most common case, does that really imply only the special case is valid? Why?

I would argue there's a large grey zone. It isn't binary, I'd say it is more of a spectrum between prescriptivism and descriptivism. After all, grammar and syntax isn't fully randomized even if largely arbitary. We make certain choices (even if we aren't aware of it) prescriptively which we try to teach each other (even if we aren't aware of it), and the mixing and noise creates a set of choices in the language actively in use that simply needs to be described for what it is. There's recurring patterns of various sources.

And if they allow one sentence to be understood by members of the intended audience that knows the common rules and context and usage well, then that's as valid as it gets. Even if only very few can understand it, the fact that it is possible is enough.

A bit like HTML in browsers - there's the written rules and there's what browsers do anyway, and what's valid in real life is whatever gets the point across.

> If you're arguing over technicalities, you are inherently adopting a prescriptivist approach.

How so? Surely there is room for debate within descriptivism as to what constitutes evidence of something being used?

> There's no rulebook when it comes to syntax (grammar), unless you're a prescriptivist.

And no two prescriptivists can agree on which rulebook to use!

Well, you can go from

"The cat meowed"

"The cat the mouse feared meowed"

If your claim is that nesting to arbitrary depths is not allowed, what is the maximum depth that is "legal"?

My guess is when the parse tree exhausts short term memory. I have no problem reading the sentence with a single nested clause ("the cat the mouse..."), but the one with a doubly nested clause is unreadable ("the dog the cat the mouse..."). Greater nesting levels might be grammatical in an abstract sense but is extremely difficult for people to understand, much like how it's possible to come up with legal C code that results in indeterminate behavior.

Probably neither the Chicago manual of style nor my Sunday school grammar book would condone such writing.

you can ... So you get unparsable things...

If it's not parseable, then surely you can't.

I meant "unparsable" in the same sense as garden path sentences are unparsable; in that, they are parsable, but you'll probably have to give it a few tries before you get it.

Another example which I have heard is:

  Throw the cow over the fence some hay.

It also reminds me of the sentence that wins the award for ending in the most prepositions:

  What did you bring that book that I didn't want to be read to out of up for?

I love that example! But I don't think it won any awards, because it's fairly easy to extend.

> What did you take the car driving the man who brought the book that I didn't want to be read to out of up away in for?

Almost-untangled form:

> For what reason did you take in the car driven away by the man who brought up the book that I did not want anyone to read words out of [the book] to me?

Although if you are being very specific, I think some syntacticians might treat the "out" in "out of" and the "up" in "bring up" as a different word classes than normal prepositions (the "out" is modifying another preposition's direction, and the "up" is a particle in a phrasal verb [1]). And I think that's one of the reasons the original form is so compelling is that you have some variance in form giving you clues -- the directional modifier, the question-inversion/wh-fronting, the salience of "bring up" -- that make it tantalizingly close to natural. Whereas mine just becomes a churn of words, at least in my reading.

[1] https://en.wikipedia.org/wiki/Phrasal_verb#Examples_of_Phras... (see the notes on distinguishing between particle & prepositional phrasals)

This is why I love Lisp so much.

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