Friday, March 25, 2022

The house with the green shutters

 Consider these two sentences:

  • I went around the house with the green shutters
In other words, the house has green shutters and I'm going around that house.
  • I went around the house with the green shutters to install
In other words, I have some green shutters I need to install on the house and I'm carrying them around the house.

These are considerably different meanings, and they have different structures from a grammatical point of view.  In the first sentence, with the green shutters is describing the house -- it has green shutters.  In the second, it is describing my going around the house -- I have the shutters with me as I go

This second sentence might be considered a garden-path sentence, which is a sentence that you have to reinterpret midway through because the interpretation you started with stops working.  Wikipedia has three well-known examples:
  • The old man the boats
  • The complex houses married and single soldiers and their families
  • The horse raced past the barn fell
If your first reaction to those sentences is "Wait ... what?" like mine was, they might make more sense with a little more context:
  • The young stay on shore.  The old man the boats.
  • The complex was built by the Corps of Engineers.  The complex houses married and single soldiers and their families.
  • The horse led down the path was fine.  The horse raced past the barn fell.
or with a slight change in wording
  • The old people man the boats
  • The housing complex houses married and single soldiers and their families
  • The horse that was raced past the barn fell
While sentences like these do come up in real life, especially in headlines or other situations where it's common to leave out words like "that" or "who" which can provide valuable clues about the structure of a sentence, they also feel a bit artificial.  An editor would be well within their rights to suggest that an author rephrase any of the three, because they're hard to read, because the whole structure and meaning aren't what you think they are at first.
  • the old man, with the adjective old modifying the noun man, changes to the old, a noun phrase made from an adjective, as the subject of the verb man.  The sentence fragment the old man becomes a complete sentence (though, granted, it's harder to leave the object off of man the boat than in a sentence like I read every day)
  • the complex houses, with the adjective complex modifying the noun houses, becomes the complex as the subject of the verb houses.  This is actually the same pattern as the first case, except that married can keep the game going (The complex houses married elements of the Rococo and Craftsman styles).  It may be worth noting that in this case, the two interpretations would generally sound distinct.  As a noun phrase, the complex houses would have the main stress on houses, while as a noun phrase and a verb, it would have the main stress on complex.
  • the horse raced, a complete sentence with raced in the simple past, becomes the horse modified by the past participle raced
Compared to these, I don't think either of the two "green shutters" sentences is particularly hard to understand.  While the change in meaning is significant, the change in structure isn't as great as in the garden-path examples.  The subject is still  I.  The verb is still went, modified by around the house.  The only difference is in what with applies to.  Every word, except possibly with, is used in the same sense in both sentences.

In technical terms, this is a syntactic ambiguity.  What's uncertain is which particular words relate to which others.  The meanings of the words themselves are the same either way.  At the very least, with remains a preposition.  In the garden-path sentences, the senses of the words, and in particular their parts of speech, change when the sentence is reinterpreted -- a lexical ambiguity, one reason to think there's something different going on in the two cases.

This sort of thing is bread and butter for linguistics and cognitive science experiments where subjects are given sentences and asked to, say, pick the picture that best matches them, with the experimenters timing the responses and looking for differences that suggest that some structures require more processing than others.  In this case, I strongly suspect that the sentences I gave would take much less time for people to sort out than the garden-path sentences.

In short, while I think that there are some similarities, I also think different things are going on in the brain when dealing with the sentences I gave, as opposed to garden-path sentences.

Even without running the experiments or considering garden-path sentences, there are some clear implications just from considering sentences like the "green shutters" ones above:
  • On the one hand, our parsing of sentences is sequential in some strong sense.  At several points, we can stop and say "This is a sentence".  If you hear nothing more, you can still work out possible meanings
    • I went around the house
    • I went around the house with the green shutters
    • I went around the house with the green shutters to install
  • On the other hand, the structure of a sentence is provisional in some sense.  After hearing I went around the house with the green shutters and associating with the green shutters with house, we can then hear to install and fairly easily re-associate with with went around the house.
  • Semantics and context affect this process.  The sentence I went around the house with the green shutters is itself ambiguous.  You could read it the same way as the other sentence, meaning that I was carrying green shutters around the house, but the house with the green shutters is much more likely to refer to the house, so you probably don't.  Similarly, putting a context sentence before a garden-path sentences makes it more likely that the garden-path sentence will make sense without re-reading.
(That last point runs counter to Chomsky's assertion that "[T]he notion of 'probability of a sentence' is an entirely useless one, under any known interpretation of this term")

Assuming that there's some sort of re-structuring going on when you hear to install after I went around the house with the green shutters, it would be interesting to see how different theories of grammar handle it.

In a phrase structure grammar, the shift between the two sentences is from a structure like
  • I [went [around [the house [with the green shutters]]]]
(a full parse tree would have a lot more to it than this) to
  • I [went [around [the house]][with the green shutters [to install]]]
That is, with the green shutters goes from being a constituent of the noun phrase (the house with the green shutters) to a constituent of the verb phrase went around the house with the green shutters to install.  From a phrase-structure point of view, the two possible readings of I went around the house with the green shutters are examples of a bracketing ambiguity, since there are two ways to put the brackets.

You can look at this as lifting [with the green shutters] out of [the house [with the green shutters]] and putting it back next to [around the house].  In principle, the place that [with the green shutters] is lifted out of can be as deep as you want: [I went [down the path [around the house [with the green shutters]]]] and so forth.  You're still moving a chunk of the parse tree from one place to another, but as the nesting gets deeper, you have to navigate through more tree nodes to find what you're moving.

In a dependency grammar, the shift is pretty simple: with switches from a dependent of house to a dependent of went (if I understand correctly, with would be a syntactic dependency of house or went, but the semantic dependency is the other way around: house or went would be a semantic dependency of went -- but there's a good chance I don't understand correctly).  Saying that I went around the house with the green shutters is ambiguous is saying that there are two possible places that with could attach as a dependency.

Consider one more sentence
  • I went around the house with the green shutters to install the awning
After seeing the awning, the shutters are back on the house and we're back where we started (and the object of install is now awning).  The fact that we can handle any of the three sentences suggests that there's something in the brain that can track both possible structures, that is, both ways of associating with, whether as a constituent or a dependency or something else, and switch back and forth between them, or in some cases even end up in a state of "Wait a sec, did you mean the shutters are on the house, or you were carrying them?"

There ought to be experiments to run in order to test this, and I wouldn't be surprised if they've already been run, but I'll leave that to the real linguists.


  1. I would say our parsing of sentences (even at the phonological level) is predictive. I'm sure we've all known people who move their lips when they listen, or finish our sentences with us. Maybe we all do it sometimes. But when someone speaks to us we begin immediately trying to guess where they're going. People with hearing loss also have to guess backwards a lot.

  2. This is a good point. From what I understand there is very strong evidence that perception in general is predictive. An interesting case is, where subjects are shown an animation of three blocks in a row. First block A moves and hits block B. Then block C starts moving, and finally block B hits block C. The assumption that A hits B, B hits C and then C starts moving is so strong that people see this even when C starts moving first, despite repeated viewings and lack of distractions.

    The thesis here is that parsing is strongly sequential in some sense, but also flexible enough to quickly account for shifts in structure. My intuition is that the brain is storing both possibilities in cases where ambiguity is likely.

    Thinking it over, this is very much in line with perception being predictive, provided predictions are flexible, which they must be in general. On hearing ... went ... house ... with ..., the brain predicts that "with" will be associated with one of "went" and "house", but updates that prediction as more information comes in. After "... with the green shutters", the prediction is that "with" will be associated with "house".

    Actually, there are probably two things going on. There's probably a prediction after "... house with" that what follows will describe the house ("with the green shutters", "with the brick sidewalk", "with the blue trim" etc.) To support making such predictions but also correcting them if needed, understanding has to be provisional. In this case, "with" is associated with "house, but it could actually be went"

    Since short-term memory is limited, there is only so much of this we can handle. An example like this is well within a typical person's capacity, while the garden-path sentences slow us down because we're not holding both possibilities in mind.

    So our understanding of language is:

    Sequential, because language is inherently sequential

    Predictive, because perception in general is

    Limited by our short-term memory

    Provisional, because both bandwidth and short-term memory are limited, so we trade off certainty for speed

    That last is probably also a feature of perception in general, but maybe more significant when it comes to language. In the case of language, it's adjustable. We can include or omit redundant information. For example, "The old man the boats" is probably OK if preceded by "The young stay on shore", but otherwise you should probably say "The old people man the boats".

    All of this can be tested experimentally, and again, I'm pretty sure lots of experiments along these lines have been done.

    And, just to beat the dead horse, none of this is even considered germane in the Chomskyan view. I know that psycholinguistics was a thing back in the 1960s, but I don't know to what extent it was underpinned by Skinner-style stimulus/response models and to what extent it allowed for the kind of stateful, predictive model that we're talking about here.