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12. What is knowledge about language?

Explanations and visualisations

 

language world

 

Most important theoretical problems

  • Arbitrariness of the sign: there is no natural connection between a word and its meaning,
    • but the Bouba/kiki effect shows some connection
    • what is the mapping between the meaning and the form?
  • Double articulation (duality of patterning): merging meaningless units into meaningful ones, merging meaningful units into higher-order meaningful units
    • sometimes only the latter regarded as language
    • relevant to the question of what are the smallest units of language
    • relevant to the question of the form of language competence: is it just one operation (merge)?
  • Displacement: we can talk about things we don't see
    • but it seems that we don't use this freedom all the time
    • relevant to the question what knowledge can be extracted from texts
  • Innateness: are we born with a specialised language faculty or it's all just general cognition?
    • a famous puzzle: Poverty of the stimulus
    • distantly relevant to generalisation and universality of NLP models
    • related to universality

 

Theoretical syntax: how do we compose phrases?

syntactic map

Source: Growing trees: The acquisition of the left periphery

  • Lexicon (vocabulary) contains two kinds of units:
    • Content units (nouns, adjective, verbs) describe entities we can imagine, e.g. things, people, animals, events and their properties
    • Function units (articles, determiners, auxiliaries, complementisers, tense, aspect, mood, conjunction, implication, negation) express relations between content units
  • Elements of lexicon are terminal nodes in a syntactic tree, non-terminal nodes are categories
  • Basic syntactic operations: merge, move, search, externalisation
  • Grammatical notions are composed of basic operations (e.g. the notion of a relative clause)
  • Merge is binary, recursive, it is not symmetric (the result of a merge is a non-terminal category of the type of one of the two merged elements), the order of merges is constant
  • Animals might be able to merge, but not recursively
  • Method: introspection, do we accept or not a string? E.g.:

 On croit [ que Jean est parti à 17h ]              'We think that John left at 17h'
 Quand croit-on [ que Jean est parti <...> ] ?      'When do we think that John left?'  

 On se demande [ qui est parti à 17h ]               'We wonder who left at 17h' 
 * Quand se demsnde-t-on [qui est parti <...> ] ?     * 'When do we wonder who left ?'

 

Information theory: text measures and quantitative laws

  • Observations of strings, typically not relating to the theoretical questions
  • Shannon entropy and complexity: text as a sequence of outcomes of a stochastic process
  • Zipf-Mandelbrot Law: the relation between word frequency and its frequency rank is universal
  • Zipf's Law of Abbreviation: the length of a word is inversely proportional to its frequency
  • Menzerath-Altmann’s Law: the bigger the whole, the smaller the parts
  • Uniform information density, constant information rate: tendency to keep the amount of information constant

 

Grammar vs. linguistics

  • Grammar is what we study in school: rules of a single language
  • Linguistics is about explaining why grammars are the way they are
    • What is common to all grammars?
    • What kinds of rules may or may not exist?
  • Most of what is called "linguistics" is about grammars (not theoretical)

 

Linguistics vs. NLP

  • Symbolic rule-based methods relied a lot on grammars
  • Statistical methods used annotated texts, Penn Treebank was an example for many others, now Universal Dependencies
  • Both rules and annotations are slightly formalised grammars, not scientific theory
  • LLMs and self-supervised learning often work without any explicit linguistic knowledge
  • Popular question: is there still any room for linguistics in NLP?