First, they offer an important perspective, one in which the
POS is one step in a more comprehensive enterprise. What’s the utility in
identifying “innate domain specific factors” of linguistic cognition? It is
“part of a larger attempt to…isolate the
role of other factors [my emphasis](1209).”
In other words, the larger goal is to resolve linguistic cognition into
four possible factors; (i) innate domain specific, (ii) innate domain general,
(iii) external stimuli, and (iv) effects of “natural law.” Understanding (i) is
a critical first step in better specifying the roles of the other three factors
and how they combine to produce linguistic competence. As they put it:
The point of a POS argument is not
to replace “learning” with appeals to “innate principles” of Universal Grammar
(UG). The goal is to identify factor (i) contributions to linguistic knowledge,
in a way that helps characterize those contributions. One hopes for subsequent
revision and reduction of the initial characterization, so that 50 years later,
the posited UG seems better grounded (1210).
I have the sense that many of those that get antsy with UG
and POS do so because they see it as smug explanatory complacency: all
linguists do is shove all sorts of stuff into UG and declare the problem of
linguistic competence solved! Wrong.
What linguists have done is create a body of knowledge outlining some
non-trivial properties of UG. In this light, for example, GB’s principles and
parameters can be understood as identifying a dozen or so “laws of grammar,”
which can now themselves become the object of further investigation, e.g. Are
these laws basic or derived from more basic cognitive and physical factors? (minimalists
believe the latter), What more basic factors are these? (Chomsky thinks Merge
is the heart of the system and speculation abounds about whether it is domain
general or linguistically specific) and so forth. The principles/laws, in other words, become
potential explananda in their own
right. There is nothing wrong with reducing proposed innate principles of UG to
other factors (in fact, this is now the parlor game of choice in contemporary
minimalist syntax). However, to be worthwhile it helps a lot to start with a
relatively decent description of the facts that need explaining and the POS has
been a vital tool in establishing these facts. Most critiques of the POS fail
to appreciate how useful it is for identifying what needs to be explained.
The second section of the BPYC paper recaps the parade case for
POS, Aux to Comp movement in Y/N questions. It provides an excellent and improved
description of the main facts that need explanation. It identifies the target of inquiry to be the
phenomenon of “constrained homophony,” i.e. humans given a word-string will understand
it to have a subset of the possible interpretations logically attributable to
it. Importantly, native speakers find both
that strings have the meanings they do and don’t have the meanings they don’t. The
core phenomenon is “(un)acceptability under an interpretation." Simple
unacceptability (due to pure ungrammaticality with no interpreations) is the
special case of having zero readings. Thus what needs explanation is how given
ordinary experience native speakers develop a capacity to identify both the possible
and impossible interpretations and thus:
…language acquisition is not merely
a matter of acquiring a capacity to associate word strings with
interpretations. Much less is it a mere
process of acquiring a (weak generative) capacity to produce just the valid
word strings of the language (1212).
As BPYC go on to show in §4, the main problem with most of
the non-generative counter proposals is that they simply misidentify what needs
to be explained. None of the three proposals on offer even discuss the problem of constrained homophony, let alone account for
it. BPYC emphasize this in their discussion of string-based approaches in §4.1.
However, the same problem extends to the Reali and Christensen bi-gram/tri-gram/recurrent
network models discussed in §4.3 and the Perfors, Tanenbaum and Regier paper in
§4.2, though BPYC don’t emphasize this in their discussion of the latter two.
The take home message from §2 and §4.1 and §4.2 is that even
for this relatively simple case of Y/N question formation, critics of the POS
have “solved” the wrong problem (often poorly, as BPYC demonstrate).
Sociologically, the most important section of the BPYC paper
is §4.2. Here they review a paper by
Perfors, Tenenbaum and Regier (PTR) that has generated a lot of buzz. They
effectively show that where PTR is not misleading, it fails to illuminate
matters much. The interested reader should take a careful look. I want to
highlight two points.
First, contrary to what one might expect given the opening
paragraphs PTR do not engage with the original problem that Aux-inversion
generated; whether UG requires that grammatical (transformational) rules be structure dependent. PTR address another question: whether
the primary linguistic data contains information that would force an ideal
learner to choose a Phrase Structure Grammar (PSG) over either a finite list or
a right regular grammar (generates only right branching structures). PTR conclude that given these three options
there is sufficient information in the Primary Linguistic Data (PLD) for an
ideal learner to choose a PSG type grammar over the other two. Whatever the
interest of this substitute question, it is completely unrelated to the
original one Chomsky posed. Whether grammars have PSG structure says nothing
about whether transformations are structure or linearly dependent
processes. This point was made as soon
as the PTR paper saw the light of day (I heard Lasnik and Uriagereka make it at
a conference at MIT many years ago where the paper was presented) and it is
surprising that the published PTR version did not clearly point out that the authors were going to discuss a completely different problem.
I assume it’s because the POS problem is sexier than the one that PTR actually
address. Nothing like a little bait and switch to goose interest in one’s work.
Putting this important matter aside, it’s worth asking what
PTR’s paper shows on its own terms. Curiously, it does not show that kids actually use PLD to choose among the three
competing possibilities. They cannot
show this for PTR is exploring the behavior of ideal learners, not actual ones.
How close kids are to ideal learners is an open question. And similar to one Chomsky long ago
considered. Chomsky’s reasons for moving from evaluation measure models (as in Aspects) to parameter setting ones (as in LGB) revolved around the computational
feasibility of providing an ordering of alternative grammars necessary for
having usable evaluation metrics.
Chomsky thought (and still thinks) that this is a very tall
computational order, one unlikely to be realizable. The same kind of feasibility issues affects
PTR’s idealization. How computationally feasible is to assume that are able to
order, compare and decide among the many grammars compatible with the data that are in the hypothesis space? The
larger the space of options available for comparison the more demanding the
problem typically is. When looking for needles, choose small haystacks. In the
end, what PTR shows is that there is usable information in the PLD that were it
used could choose PSGs over the two other alternatives. It does not show that
kids do or can use this information effectively.
The results are IMHO more modest still. The POS argument has
been used to make the rationalist point that linguistically capable minds come
stocked full of linguistically relevant information. PTR’s model agrees. The
ideal mind comes with the three possible options pre-coded in the hypothesis
space. What they show is that given
such a specification of the hypothesis space, the PLD could be used to choose
among them. So, as presented, the three grammatical options (note the domain specificity: it's grammars in the hypothesis space) are given (i.e. innately
specified). What's “learned” (i.e. data driven) is not the range of options
but the particular option selected. What pposition does PTR argue against? It appears to be the
following position: only by delimiting the hypothesis space of possible
grammars so as to exclude all but
PSGs can we explain why the grammars attained are PSGs (which of course they
are not, as we have known for a long while, but ignore that here). PTR's proposal is that it's ok to widen the options open for consideration to include non-PSG grammars
because the PLD suffices to single out PSGs in this expanded space.
I can’t personally identify any generativist who has held
the position PTR targets. There are two dimensions in a Bayesian scenario: (i)
the possible options the hypothesis space delimits, (ii) a possible weighting
of the given options giving some higher priors than others (making them less
marked in linguistic terms). These
dimensions are also part of Chomsky’s abstract description of the options in Aspects chapter 1 and crops up in
current work on questions of whether some parameter value is marked. So far as I can tell, the rationalist
ambitions the POS serves are equally well met by theories that limit the size
of the hypothesis space and those that widen it but make some options more
desirable than others via various kinds of (markedness) measures (viz. priors).
Thus, even disregarding the fact that the issue PTR discuss is not what
generativists mean by structure dependence, it is not clear how revelatory
their conclusions are as their learning scenario assumes exactly the kind of
richly structured domain specific innate hypothesis space the POS generally aims to
establish. So, if you are thinking that PTR gets you out from under rich domain
specific innate structures, think again.
Indeed if anything, PTR pack more
into the innate hypothesis space than generativists typically do.
Rabbinic law requires that every Jew rehash the story of the
exodus every year on Passover. Why? The rabbis answer: it’s important for
everyone in every generation to personally
understand the whys and wherefores of the exodus, to feel as if s/he too were personally liberated, lest it’s forgotten
how much was gained. The seductions of
empiricism are almost alluring as “the fleshpots of Egypt.” Reading BPYC responsively,
with friends, is excellent antidote, lest we forget!
