The view from linguistics
Comment on "Approaching human
language with complex networks" by
Cong and Liu
Richard Hudson
Research Department of Linguistics, University College London
The study of language as a complex network (as described by Cong and Liu - Cong and Liu
2014 ) comes at a good time for a theoretical linguist such as me, because it coincides with a
number of other developments which it complements well. On the other hand, it also presents
important new challenges for our research, not least Cong and Liu's challenge of providing
the 'much deeper explanation' for the network properties that this new research reveals.
The most obvious challenge for theoretical linguistics is to produce a model of language as a
complex network - or, indeed, to agree on whether such a model is even desirable. It is
obvious that the lexicon is a network, in which lexical items are interconnected in complex
ways by their shared phonology, morphology, syntax and meaning; for example, the noun
TACK has phonological links to ATTACK and TAX; morphological links to the verb TACK and
to TACKY; syntactic links to all other nouns and to collocating adjectives such as SHARP; and
semantic links to NAIL and HAMMER. Moreover, it is equally obvious how these links are
established via intervening structures such as the syllable /tak/, the morpheme {tack}, the
word-class 'noun' and the syntactic relation of modification, and semantic elements such as
'hit' and 'sharp metal spike'. Better still, there is massive evidence from psychological
'priming' experiments that these links are psychologically real: thanks to spreading activation,
hearing any of these related words raises the activity level of TACK so that this is easier to
access than it would be without the priming. One of the recent developments in linguistic
theory has been increased interest in modelling these network properties, but this has
coincided with a rejection of the boundary between the lexicon and the grammar, so there are
now some reasonably well-developed network models of the whole of language, including
the 'rules' of grammar (Bates and Goodman 1997, Bybee 2010, Goldberg 2006, Langacker
2007, Hudson 2007). Arguably the most developed and comprehensive of these models is
Word Grammar (Hudson 1984, Hudson 1990, Hudson 2007, Hudson 2010), which I assume
in my remaining comments.
What linguistics can contribute to the research on complex networks is a detailed formal
structure for the networks concerned. The network of language is not simply a set of
associations; rather, the links are typed, so a word's relation to its meaning is quite different
from its relation to its word class and to its morphological form. The most important relation
is class-membership, carried by a relation widely named 'isa' (as in 'TACK isa noun'), but
there are not only a handful of other special relations but also an open-ended, learnable and
hierarchically organised set of relational concepts such as 'subject', 'meaning' and 'base'. One
of the challenges for network research is to find out how these different relations interact in
producing the overall profile for a language's grammar.
Another contribution from linguistics is a theory of how the language system is related to its
use - in Cong and Liu's terms, how the permanent 'static' network relates to the 'dynamic' one.
The leading idea here is that the word-tokens of usage (actual speech events) become
temporary parts of the permanent network, so (according to Word Grammar) the dynamic and
static networks are actually a single network which is constantly changing. The permanent
part is what we use in both creating and interpreting word-tokens, and the dynamic part feeds
back into the permanent part as we learn new patterns and absorb the statistical properties of
experience. This process is called 'usage-based learning', and should explain at least some of
the observed properties of the permanent network; for example, scale-free networks are
typically due to learning in which 'the rich get richer' as we try to fit new experiences into
our existing knowledge.
There are several strands of linguistic research which develop the consequences of usagebased learning, including quantitative sociolinguistics (Hudson 1996) and historical studies of
how 'lexical' patterns turn gradually into grammatical patterns (Traugott and Trousdale 2013).
All of these stand to gain from the global perspective of network analysis on their 'micro'
concerns.
References
Bates, Elizabeth and Goodman, Judith 1997. 'On the inseparability of grammar and the
lexicon: evidence from acquisition, aphasia and real-time processing.', Language and
Cognitive Processes 12: 507-584.
Bybee, Joan 2010. Language, Usage and Cognition. Cambridge: Cambridge University Press
Cong, Jin and Liu, Haitao 2014. 'Approaching human language with complex networks',
Physics of Life Reviews [this issue]
Goldberg, Adele 2006. Constructions at work. The nature of generalization in language.
Oxford: Oxford University Press
Hudson, Richard 1984. Word Grammar. Oxford: Blackwell.
Hudson, Richard 1990. English Word Grammar. Oxford: Blackwell.
Hudson, Richard 1996. Sociolinguistics (Second edition). Cambridge: Cambridge University
Press
Hudson, Richard 2007. Language networks: the new Word Grammar. Oxford: Oxford
University Press
Hudson, Richard 2010. An Introduction to Word Grammar. Cambridge: Cambridge
University Press
Langacker, Ronald 2007. 'Cognitive grammar', in Dirk Geeraerts & Hubert Cuyckens (eds.)
The Oxford Handbook of Cognitive Linguistics. Oxford: Oxford University Press,
pp.421-462.
Traugott, Elizabeth and Trousdale, Graeme 2013. Constructionalization and constructional
changes. Oxford: Oxford University Press