The SMT again

Two revisions below thx to Ewan spring a thinko, a slip of the mind.

I have recently urged that we adopt a particular understanding of the Strong Minimalist Thesis (SMT) (here).  The version that I favor treats the SMT as a thesis about systems that use grammars and suggests that central features of the grammatical representations that they use will be crucial to explaining why they are efficient. If this proves to be doable, then it is reasonable to describe FL and the grammars it makes available as “well designed” and “computationally efficient.” Stealing from Bob Berwick (here), I will take parsing efficiency to mean real time parsing and (real time) acquisition to mean easy acquisition given the PLD.  Put this all together and the SMT is the conjecture that the grammatical format of Gs and UG is critical to allowing parsers, acquirers, producers, etc. to be very good at what they do (i.e. to be well-designed). On this view, grammars are “well designed” or “computationally efficient” in virtue of having properties that allow their users to be good at what they do when such grammars are embedded transparently within these systems.

One particularly attractive virtue of this interpretation (for me) is that I understand how I could go about empirically investigating it.  I confess that this is not true for other versions of the SMT that talk about neat fits between grammar and the CI interface, for example. So far as I can tell, we know rather little about the CI interface and so the question of fit is, at best, premature. On the other hand we do know a bit about how parsing works and how acquisition proceeds so we have something to fit the grammar to.[1]

So how to proceed? In two steps I believe. The first is to see if use systems (e.g. parsers) actually deploy grammars in real time, i.e. as they parse. Thus, if it is true that the basic features of grammatical representations are responsible for how (e.g.) parsers manage to efficiently do what they do then we should find real time evidence implicating these representations in real time parsing. Second, we should look for how exactly the implicated features manage to make things so efficient. Thus, we should look for theoretical reasons for why parsers that transparently embody, say, Subjacency like principles, would be efficient.  Let me discuss each of these points in turn.

There is increasing evidence from psycho-ling research indicating that real time parsing respects grammatical distinctions, even very subtle ones.  Colin Phillips is a leader in this kind of work and he and his (ex) students (e.g. Brian Dillon, Matt Wagers, Ellen Lau, Dave Kush, Masaya Yoshida) have produced a body of work that demonstrates how very closely parsers respect grammatical conditions like islands, c-command, and local binding domains. And by closely I mean very closely.  So, for example, Colin shows (here) that online parsing respects the grammatical conditions that license parasitic gaps. So, not only do parsers respect islands, but they even treat configurations where island effects are amnestied as if they were not islands. Thus, parsers respect both the general conditions that grammars lay down regarding islands and the exceptions to these general conditions that grammars allow. This is what I mean by ‘close.’

There is a recent excellent demonstration of this from Masaya Yoshida, Lauren Ackerman, Morgan Purier and Rebekah Ward (YLPW) (here are slides from a recent CUNY talk).[2] YLPW analyzes the processing of backward sluicing constructions like (1):

(1)  I don’t recall which writer, but the editor notified a writer about a new project

There is an ellipsis “gap” right after which writer that is redeemed by anchoring it to a writer in the following sentence. What YLPW is looking to determine is whether the elided gap site is sensitive to online parsing effects. YLPW uses a plausibility effect as probe as follows.

First, it is well known that a wh in CP triggers an active search for a verb/gap that will give it an interpretation. ‘Active’ here means that the parser uses a top down predictive process and is eagerly looking to link the wh to a predicate without first consulting bottom information that would indicate the link to be ill-advised. YLPW show that the eagerness to “fill a gap” is as true for implicit gaps within ellipsis sites as it is for “real” gaps in regular wh sentences.  YLPW shows this by demonstrating a plausibility effect slowdown in sentences like (2a) parallel to the ones found in (2b):

(2)  a. I don’t remember which writer/which book, but the editor notified a writer about a new book

b. I don’t remember which writer/which book the editor notified GAP about a new book

When the wh is which book then there is a significant pause at notified in both sentences in (2), as contrasted with the same sentences where which writer is the antecedent of the gap.  This is because parsers, we know, greedily try and relate the wh to the first syntactically available position encountered and in the case of which book the wh is not a plausible filler of the gap and the attempted filling results in a little lingering about the verb (*notify this book about…). If the antecedent is which writer no such pause occurs, for obvious reasons.  The plausibility effect, then, is just a version of the well-known filled gap effect, with a little semantic kicker to add some frisson. At any rate, the first important discovery is that we find the same plausibility effect in both (2a) with the gap inside a sluiced ellipsis site, and (2b) where the gap is “overt.”

The next step is to see if this plausibility/filled gap effect slowdown occurs when the relevant antecedent for the sluiced ellipsis site is inside an island. It is well known that ellipsis is not subject to island restrictions. Thus, if the parser cleaves tightly to the distinctions the grammar makes (as the SMT would lead us to expect) then we should find plausibility slowdowns except when the gap is inside an ellipsis site for the latter are not subject to island restrictions [and so should induce filled gap/plausibility effects (added: thx Ewan)].  And that’s exactly what YLPW find. Though plausibility effects are not found at notified in cases like (3) they are found in cases like (4) where the “gap” is inside a sluice sight.

(3)  I don’t remember which book [the editor who notified the publisher about some science book] had recommended to me

(4)  I don’t remember which book, but [the editor who notified the publisher about some science book] recommended a new book to me

This is just what we expect from a parser that transparently embeds a UG like grammar that treats movement but not ellipsis as a product of (long) movement.

The conclusion: it seems that parsers make just the distinctions that grammars make when they parse in real time, just as the SMT would lead us to expect.

So, there is growing evidence that parsers transparently embed UG like grammars.  This readies us for the second step. Why should they do so?  Here, there is less current research that bears on the issue. However, there is work from the 80s by Mitch Marcus, Bob Berwick and Amy Weinberg that showed that a Marcus style parser that incorporated grammatical features like Subjacency (and, interestingly, Extension) could parse sentences efficiently (effectively, in real time).  This is just what the doctor ordered. It goes without saying (though I will say it) that this work needs updating to bear more directly on the SMT and minimalist accounts of FL. However, it provides a useful paradigm of how one might go about connecting the discoveries concerning online parsing with computational questions of parsing efficiency and their relationship to central architectural features of FL/UG.

The SMT is a bold conjecture. Indeed, it is likely false, at least in fine detail. This does not, however, detract from its programmatic utility.  The fact is that there is currently lots of research that can be understood as bearing on its accuracy and that fruitfully brings together work in syntax, psycholinguistics and computational linguistics.  The SMT, in other words, is a terrific hypothesis that will generate fascinating work regardless of its ultimate empirical fate.  That’s what we want from a research program and that’s something that the Strong Minimalist Thesis is ready to deliver. Were this all that the Minimalist Program provided, it would have been enough (dayenu!). There is more, but for the nonce, this is more than enough. Yay, for the Minimalist Program!!!

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[1] Let me modulate this: we know something about some other parts, see here for discussion of magnitude estimation in the visual domain. Note that this discussion fits well with the version of the SMT deployed here precisely because we know something about how this part of the visual system works. We cannot say as much about most of the other parts of CI. Indeed, we don’t really know how many “parts” CI has.

[2] They are running some more experiments, so this work is not yet finished. Nonetheless, it illustrates the relevant point well, and it is really fun stuff.