Parametric Variation (PV) has been
under attack. Despite Berwick &
Chomsky’s (2008:8) assertion that: “... principles do not determine the answers
to all questions about language, but leave some questions as open parameters”,
there has been widespread reluctance to accept the existence of parameters as
opposed to particular rules (see e.g. Newmeyer 2005, Boeckx 2010). A vigorous
counter-movement (see e.g. the special issue of Theoretical Linguistics 36.1, devoted to Holmberg 2010) shows that no
consensus has been reached. There is a parallel with human types where
the apparent obvious diversity of different ‘races’ disguises profound
underlying unity, and specifying the nature of the variation is difficult. It is against this background that I want to raise the issue of the
evolvability of PV: how plausible is the claim that PV has evolved, rather than
the sceptics’ claim that aggregations of unconnected rules have developed? If
it could be demonstrated that PV could not have evolved this would constitute a
powerful argument in favour of such scepticism. Providing a sketch of how PV
might have evolved doesn’t, of course, show that it did, but it would remove
one brick from the sceptics’ edifice.
PV theory unifies two different
domains: typology and acquisition. Variation among the world’s languages (more
accurately the set of internalised I-languages, Chomsky 1986) is defined in
terms of parametric differences and, in first language acquisition the child’s
task is reduced to setting the values of such parameters on the basis of the
stimuli it is exposed to – utterances in the ambient language. Given the
strikingly uniform success of first language acquisition, it follows that “the
set of possibilities [must] be narrow in range and easily attained by the first
language learner” (Smith 2004:83). By
hypothesis, the principles do not vary from child to
child or from language to language so, as
Chomsky (2006:183) puts it, “acquisition is a matter of
parameter setting, and is therefore divorced entirely from … the principles of
UG.”
The theory is at once ‘internalist’
(i.e. it is a theory of states of the mind/brain, pertaining to knowledge which
is largely unconscious), and universalist. An immediate implication of this
position is that the range of parametric choices is known in advance and, as a
corollary, it claims that acquisition is largely a process of ‘selection’
rather than instruction (see Piattelli-Palmarini 1989) and that such
acquisition is likely to take place in a critical period or periods. For some, “all syntactic
variation is parametric” (Kayne, 2005; Manzini & Savoia, 2007; Roberts
& Holmberg, 2010, etc.), but this is undesirable because too unconstrained.
If not all variation is parametric, the responsibility of parametric theory is
reduced and we need to redefine the
nature and scope of ‘parametric’
variation. I presuppose a 3-way distinction among Universal
Principles, Parameters, and Accidents – typified by irregularities of
morphology. Thus we have not only a distinction between Principles and Parameters but also Constraints on
Parameters to differentiate parametric choices from ‘Accidents’. That is, we
need identity criteria for
parameters (see Smith & Law 2009 for discussion).
Further, theoretical
consistency demands that we have the
same criteria for syntax and
phonology and (if there are relevant examples) for semantic choices at
the C-I interface (cf. Chierchia, 1998) and (if definable) for systematic morphological
variation. For current purposes I am happy to go along with Chomsky’s
observation that “parametrization and diversity too
would be mostly – maybe entirely
– restricted to
externalization,” (Chomsky 2010:60; to “language shorn of the properties of the
sound system” as Smith 2004:43, puts it) hence mainly morphology and phonology.
One reason for the multiplicity of languages is then that “the problem of
externalization can be solved in many different and independent ways,”
(Chomsky, 2010:61) where moreover these may all be ‘optimal’ in different ways.
I should note in passing that I am unconvinced by such claims as
“To
externalize the internally generated expression ‘what John is eating what’, it
would be necessary to pronounce ‘what’ twice, and that turns out to place a
very considerable burden on computation” (Berwick & Chomsky 2008:11). The
burden seems slight, especially given that in first language acquisition
children regularly repeat material ‘unnecessarily’ (see e.g. Crain &
Pietroski’s 2002: ‘What
do you think what pigs eat?’).
So, is PV
evolvable? One stance it is tempting to adopt is that evolvability[1] is simply another criterion characterising PV. In the absence (in
the domain of language) of some independent characterisation of evolvability,
however, such a claim would be circular. Indeed, like Fodor &
Piattelli-Palmarini (2010:159) I am sceptical that there is any level of
evolutionary explanation: “Natural history is just one damned thing after
another”, in their colourful terms. That is, there is no unified theory
accounting for the fixation of phenotypic traits in natural populations, and
there is equally no unified theory accounting for language typology, as witness
the ‘accidents’ mentioned above. Evolution is not explicable in terms of a
single theory. Even so, variation emerged so there had better be an account. More
positively, it seems uncontentious that, as Bennett (2010:31) puts it,
“macroevolution may, over the longer term, be driven largely by internally
generated genetic change, not adaptation to a changing environment”, that
“mutations occur continually, without external influence”, and that “a single
small change can have far-reaching and unpredictable effects”. Parallels with
language are obvious, though I would not wish to deny the relevance of ‘external
influence’.
There are three
strands in the alternative account I wish to provide. First, there is evidence for genetically
determined individual variation in knowledge and use of language, including not only pathological but also
typically developing populations.
Second, it is plausible to postulate that language learners find
different solutions to the problem of externalisation more or less
‘accessible’. Third, the linguistic typology
we see today is asymmetric, with only a subset of the logically possible
languages being attested: the observation which initially made
(macro-)parameters plausible. But the typology is not as skewed as predicted:
too many of the logical possibilities actually are attested, an observation
which makes some, conceivably all, such parameters suspect. The classic example
is the fractionation of the ‘pro-drop parameter’ when it was observed that the
individual sub-parts dissociated. Nonetheless, I think that this imperfect
typology is more robust than is standardly accepted, and probably arose as the
result of a learning strategy that is still operative in first language
acquisition. If correct, this suggests
that rejecting PV on these grounds would be premature.
Assuming a stage in
hominid evolution by which language has appeared, we need to motivate the
development in subsequent generations of PV. By hypothesis, the first language
to evolve had no PV. That is, the existence, and hence emergence, of PV
presupposes the prior evolution of language. Berwick & Chomsky (2008) argue
that the source of PV is externalisation and that there is “no reason to
suppose that solving the externalisation problem involved an evolutionary
change – that is, genomic change”. This claim is not, however, apodictic: the
switch-box metaphor suggests that the range of parametric variants is
‘antecedently known’, and implicit in ‘antecedently known’ is genetic control,
and in the same paper they talk of “the evolution ... of the mode of
externalisation”. We need a more nuanced account to resolve the tension caused
by the apparent inconsistency: solving the problem of externalisation probably
did not ‘involve’ an evolutionary change in the sense of being caused by such
change, but the solution may well have given rise to a situation in which
evolutionary, and genomic, change could occur.
In what follows I
suggest how in principle PV might have become genetically encoded and, in doing
so, explore the need for a transition in looking at PV from a stance where
typological variation is primary and first language acquisition secondary, to
one (now) where the primary motivation is acquisition and accounting for
typological variation is just a useful bonus.
To see how plausible this transition is we turn to the first of the
three strands mentioned above, beginning with the status of genetic factors in
the knowledge and use of language. It is presumably uncontroversial that
absolute (i.e. universal) principles such as structure-dependence must have
become genetically encoded with no individual variation.
In general,
genetic and neuro-imaging studies have provided cogent evidence only for the
aetiology of pathological as opposed to typical development (see e.g.
Stromswold, 2010:181; O’Connor et al, 1994). However, it is known on the basis
of twin studies (Stromswold, 2010) that different aspects of our linguistic
knowledge and its use are subject to
genetically determined variation. That is, linguistic variation, which may be
due to genetic or environmental factors, is pervasive among individuals in a
population, even between siblings, but monozygotic (MZ, or ‘identical’) twins
are linguistically more similar to each other than are dizygotic (DZ, or ‘fraternal’)
twins, implying that genetic factors are responsible for this variance. Consider
some examples from Stromswold (2010). In phonology “two-thirds of the variance
in phonemic awareness, and 15 percent of the variance in articulation is due to
heritable factors” (p.181); “for over 90 percent of the morphosyntactic tests,
the MZ correlation coefficient was larger than the DZ correlation coefficient”;
“about a third of the variance in vocabulary” is due to heritable factors.
Strikingly, except for the onset of babbling, there is considerable genetic
overlap[2] in the emergence of linguistic milestones (e.g. the onset of first
words and sentences), and even fluency of language use is subject to genetic
conditioning.
All this variation
falls on a continuum which crucially includes typical development, suggesting
that the emergence of individual linguistic differences, both random and
principled, is ubiquitous. More importantly it suggests how cross-linguistic
variation might emerge, perhaps ultimately becoming genetically conditioned.
A possible
scenario, involving the second strand mentioned above, might be that choices
that are now parametric were originally the result of randomly induced rules. Some choices of rule then clustered,
presumably because of perceived structural parallelism, leading to a situation
where some of these ‘clustered’ choices were more accessible than others and therefore
came to predominate over time. The increased frequency of these patterns
facilitated learning and ultimately gave rise to parametrisation. For instance,
some properties that are now described as parts of a single macro-parameter
(and that therefore participate in parametric cascades) might have developed
from alternatives ranked in accessibility according to their conceptual
salience or facilitatory effect on processing, where this could vary according
to viewpoint – parser or producer. As a simplistic example, the possibility of
null subjects is differentially advantageous to the speaker, for whom it
constitutes an economical saving of effort, and to the hearer, for whom it
constitutes an interpretive problem.
To make the
proposal clearer, I first present an abstract schema and then illustrate it
with real examples. Learners might
associate property X with property Y or with property Z. Such association in
the mind of the child could lead to short-cuts in the learning process: learner
A might jump to the conclusion C1 that observing X licensed the
conclusion that Y, learner B might jump to the conclusion C2 that
observing X licensed the conclusion that Z.
In each case the provisional conclusion would result in a difference in
knowledge which itself could result in a skewing of the primary linguistic data
for the next generation. Such skewing
would in turn make C1 or C2 more accessible. In an
environment gradually enriched by the presence of more and more speakers, both
patterns could become equally accessible to some populations with the result
that arbitrary or random choice (or no choice) might ensue. The next, crucial,
stage is whether the learners’ assumptions become consolidated as parametric
alternatives or remain, as they originated, as learning-theoretic strategies.
The latter possibility finesses, or at least postpones, the problem of how a
subset of linguistic alternatives become genetically encoded – but suggests
that ‘antecedently known’ may have a learning-theoretic not a
linguistic-theoretic domain of application.
Working in an
early parametric framework, but one which suffices for exegetical purposes,
Lefebvre (1998:355ff.) discusses a number of correlations between putative
parametric choices, where the existence of property A licenses the assumption
that the language exhibits property B or property C, leading potentially to the
existence of macro-parametric variation. Thus, the presence of serial verb
constructions correlates with either the absence of prepositions or the absence
of inflectional morphology; the presence of double object constructions
coincides with either the presence of preposition stranding or with the
direction of theta-role assignment. Lefebvre then observes that all of these
correlations fail, either because there are attested exceptions to them or
because they are theoretically unmotivated.
This initially disappointing fact has one redeeming feature: it suggests
that one might entertain an interpretation on which modes of externalisation were
originally unconstrained, and that systematic correlations among linguistic
properties might have emerged gradually, giving rise to a relatively
constrained set of systems. Crucially the correlations need not emerge as
absolutes but as strong tendencies forming the basis for a learning strategy.
A simpler
illustration is provided by the case of head-direction. For the child, as for
the linguist, the underlying assumption is that sub-parts of the grammar,
including head-directionality, are ‘harmonic’ or ‘consistent’. The child
acquiring its first language observes that verbs precede their objects and then
jumps to the conclusion, on the basis of minimal – or even no – further
examples, that its language is head-first.
If the language is consistent, nothing more needs to be said, or
acquired; if it is inconsistent, then positive evidence will lead to
traditional learning modifying the parameter setting. That is, the parametric
story predicts the need for learning in certain situations and hence, importantly,
also predicts particular error patterns (over-generalisation to the harmonic)
in such situations. If there is positive evidence of the kind mentioned it
follows that PV is not conceptually necessary, though it may nonetheless be
empirically correct.
A corollary of
this view is that if such asymmetric choices arose in individuals and then
groups of individuals, it would eventuate in typological asymmetry of the
well-known kind. That is, greater accessibility would lead not to the kind of
absolutes characteristic of standard accounts of PV but to statistical
asymmetry in the incidence of harmonic combinations. This more realistic result
emerges from invoking the role of learning theory rather than explaining
everything in terms of knowledge of language.
Just as I insisted
that the criteria for PV extend to phonology as well as syntax, I require the
same for evolvability. A phonological example of possible emergent
parametrisation can be seen in the differential treatment of post-consonantal
glides discussed in Smith & Law 2009. Yip (2003:804) argued that some
speakers treat a post-consonantal glide as a secondary articulation of the
consonant, others as a segment in its own right: “the rightful home of /y/ [is]
underdetermined by the usual data, leaving room for variation.” Her conclusion was that “speakers opt for
different structures in the absence of conclusive evidence for either.” We used Yip’s observation to argue that this did not exemplify PV
because it was not deterministic, but it may still represent a step along the
path to parametrisation. If one pattern
becomes more frequent, perhaps at random, it may gradually become consolidated
as a parameter.
So I think it is clear that, and even how,
PV could have evolved – a view defended in more detail by Roberts &
Holmberg 2010 – and conclude with a summary list of possible stages in parametric
evolution.
a. Random
variation gives rise to choice for the next generation, resulting in
incipient
typology.
b. First language learners find the solutions
to the problem of externalisation provided by this choice more or less
‘accessible’.
c. Hence
the linguistic typology became asymmetric (as we see today), with
only
a subset of the logically possible languages being attested.
d. Current
evidence for genetically determined individual variation in knowledge
and use of language in all populations suggests genomic change.
e. The asymmetric typology in (c) is more revealing than is
standardly accepted, and
probably arose as the result of a learning strategy that is
still operative in first language
acquisition.
f. The putative genetic encoding of PV suggests
there was a transition from typological variation to acquisition, where the
plausibility of the transition depends on the status of genetic factors in the knowledge
and use of language.
g. Universal principles such as
structure-dependence must have become genetically encoded
with no individual variation. So such encoding is in
principle possible.
h. Twin studies show that different aspects
of our linguistic knowledge and its use are
subject to genetically determined
variation.
i. All this variation falls on a
continuum which includes typical development, suggesting
that the emergence of individual linguistic differences is
ubiquitous and that cross-
linguistic variation might become genetically conditioned.
j. The child assumes that sub-parts of
the grammar are ‘harmonic’ or ‘consistent’. Hence:
some choices of rule cluster because
of perceived structural parallelism, leading to
short-cuts in the learning process. Some such clusters
became more accessible than others
so came to predominate. Increased frequency of these
patterns facilitated learning and
gave rise to incipient parametrisation depending on the
conceptual salience or facilitatory
effect on processing – either parsing or production of the
patterns.
k. The data are not always clear-cut and
learners may associate property X with property Y
(C1) or with property Z (C2). Each
provisional conclusion results in a skewing of the
primary linguistic data for the next generation.
l. Such
skewing makes C1 or C2 more accessible. In an environment
gradually enriched by
more and more speakers, both patterns could become equally
accessible with the result that arbitrary or random choice (or no choice) might
ensue.
m. Such asymmetric choices by (groups of)
individuals would eventuate in typological
asymmetry. Greater accessibility would lead not to the
absolutes characteristic of
standard accounts of PV but to statistical asymmetry in the
incidence of harmonic combinations. This result emerges from invoking learning
theory rather than relying exclusively on knowledge of language.
n. A crucial issue is whether the
learners’ assumptions become consolidated as parametric
alternatives or remain, as they originated, as
learning-theoretic strategies. The latter
possibility
suggests that ‘antecedently known’ may have a learning-theoretic not a
linguistic-theoretic
domain of application: a ‘third
factor’ effect.
o. The current parametric story predicts
the need for learning in certain situations and hence
also predicts particular error patterns
(over-generalisation to the harmonic). If there is
positive evidence it follows that PV is not conceptually
necessary, but it may nonetheless
be empirically correct.
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MA: MIT Press.
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