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LIN1180 Semantics Lecture 4

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we're more likely to say 'that's a dog' than 'that's a dachshund' ... but in most cases, saying 'x is a dachshund' is too specific... Semantics -- LIN 1180 ... – PowerPoint PPT presentation

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Title: LIN1180 Semantics Lecture 4


1
LIN1180 Semantics Lecture 4
  • Albert Gatt

2
Goals of this lecture
  • We revisit
  • The contrast between denotational and
    representational theories of meaning
  • We look at
  • How scientists have studied the mental
    representation of concepts, the units of
    thought

3
Part 1
  • The denotational and representational theories
    revisited

4
The denotational theory (I)
  • Proposes that meaning involves establishing a
    direct relationship between linguistic
    expressions and the world
  • Word meaning
  • dog denotes the set of things in the world which
    are dogs
  • Sentence/propositional meaning
  • My dog ate the carpet denotes a situation in
    which it is the case that a dog, belonging to the
    speaker, ate the carpet

5
The denotational theory (II)
  • This theory has its roots in the correspondence
    theory of meaning and truth
  • A sentence is true if and only if it denotes a
    situation in the world.
  • Important figures include logician Alfred Tarski,
    and semanticist Richard Montague. Also the early
    work of Ludwig Wittgenstein.
  • It dominates the tradition of formal semantics
  • Based on a realist or objectivist view We can
    obtain objective knowledge of what is out there

6
Challenges to the denotational theory
  • In its simplest form, the theory says
  • semantics denotation
  • proper names denote individuals
  • common nouns denote sets of things
  • verbs denote actions
  • But some words seem to denote nothing at all!
  • Words for imaginary things (unicorns), function
    words (not, with)
  • This is usually resolved by saying that
    expressions have sense, which determines
    denotation and reference
  • Expressions may have sense but simply no
    denotation!
  • Others may denote to the same things, but differ
    in their sense.

7
Concepts
  • The denotational theory tends to be adopted in
    the tradition of formal semantics
  • applies the tools of logical analysis to the
    study of meaning
  • More cognitively-oriented theories tend to adopt
    some version of the representational theory
  • crucially, the study of meaning involves the
    study of conceptual structure

8
The representational theory (I)
  • The meaning of linguistic expressions is a mental
    representation (CONCEPT)
  • So expressions are meaningful, and denote things,
    because they are associated with something in our
    heads.
  • So the relationship between language and world is
    indirect or mediated.

kelb
9
The representational theory (II)
  • Has strong ties with the tradition of
    phenomenology in philosophy
  • Branch of philosophy concerned with perception,
    mental representation etc
  • Argues that our interaction with reality is
    indirect, via our perceptions and representations
  • Has informed a lot of contemporary work in
    psychology, especially on the study of concepts

10
Part 2
  • Concepts and mental representation

11
A word for every object
  • In effect, Funes not only remembered every leaf
    on every tree of every wood, but even every one
    of the times he had perceived or imagined it.
    He knew that at the hour of his death he would
    scarcely have finished classifying even all the
    memories of his childhood.
  • (J.L. Borges, Funes the memorious)

12
Why concepts?
  • Without a way of categorising things and
    situations, human cognition would break down.
  • Concepts provide
  • a way to organise similar experiences under more
    general categories
  • a way of establishing relationships among those
    categories
  • a way of making generalisations about things.
  • Concepts are the atoms of thought.

13
Conceptual structure and language
  • Presumably, words and constituents map to
    conceptual elements.
  • E.g. Jackendoff (2002) proposes a three-level
    theory of language
  • phonological structure
  • syntactic structure
  • conceptual structure
  • Rules to map from one level to the other.
  • The rules mapping from linguistic to conceptual
    structure define an interface between language
    and other cognitive functions.

purely linguistic
purely linguistic
general cognition
14
Other theories
  • Other theories (contra Jackendoff), propose a
    level of semantic structure which is properly
    linguistic.
  • This intervenes between conceptual structure and
    linguistic structure.

15
Whats in your head?
  • Under the representational view, concepts
    underlie the meanings of words
  • What could a concept be?

16
Concepts as images (I)
  • Do we have a mental picture of things?
  • But not everybody has the same picture
  • So how do we understand eachother?

kelb
17
Whats your picture of DOG?
???
kelb
18
Beyond the image theory
  • Concepts must be something more abstract than
    concrete images
  • This is still a huge topic in current
    psychological and semantic theory
  • Lets look at some possibilities

19
Theories of concepts I the classical view
  • A concept like GIRL is simply the bare minimum
    necessary to distinguish it
  • GIRL human, not adult, female
  • Essentially, to know a concept to know a
    definition.
  • View dating back to Aristotle.

20
Objections to the classical view
  • Most concepts simply cant be analysed like this.
  • What are the necessary and sufficient conditions
    for the concept GAME? (Wittgenstein, 1953)
  • Many concepts have fuzzy boundaries.
  • We often use words without knowing the true
    nature of things
  • Do you need to know the chemical make-up of
    aluminium in order to know the word?
  • Putnam (1975) We rely on experts a lot of the
    time, a division of linguistic labour

21
The causal theory (Putnam, Kripke)
  • Recall from Lecture 2
  • Causal theory states that proper names identify
    individuals because of some initial event in
    which the connection is set up
  • Others receive the name and use it, even if
    they dont know what caused the association
  • Some argue that nouns that denote natural kinds
    work the same way. E.g. GOLD
  • Someone must have discovered it and called it
    gold
  • An expert would know exactly what it takes for a
    substance to qualify as gold
  • We dont need to know, we simply use the term
    because of the original christening

22
Theories of concepts II prototypes
  • Extensively studied by psychologist Eleonor Rosch
    in the 1970s.
  • Central argument is that concepts have internal
    structure, with some members being better than
    others
  • Example BIRD
  • central/typical members (sparrow)
  • peripheral members (ostrich, penguin)
  • There is a gradient from centre to periphery

23
Prototype example
24
Evidence I Goodness of exemplar
  • Experimental subjects are shown pictures of
    different things of the same category (e.g.
    VEGETABLE)
  • Asked to rate each one in terms of how good an
    example of the category they are.
  • E.g. carrot, turnip, cabbage, beetroot, lemon
  • Subjects tend to be quite homogeneous in agreeing
    on what typical and not-so-typical members are.
  • (As long as they come from the same cultural
    group)

25
Evidence II Prototype effects
  • Order of mention Under time pressure, when asked
    to list members of a category, subjects tend to
    list the prototypical members first.
  • Acquisition prototypical members tends to be
    acquired first.
  • Learning kids learn new words faster if taught
    the meaning with reference to the prototype.

26
Consequences of prototypes
  • Views concepts as having fuzzy boundaries
  • some things might qualify as CHAIR, but they
    might not be typical
  • some things qualify as RED, but others are
    between RED and PURPLE
  • This isnt about what the world is like, but
    about how people represent the world.

27
Part 3
  • Conceptual organisation

28
Feature-based representation
  • Prototype theory raises the problem of how
    concepts are actually represented in the mind.
  • One possibility is to list features of members of
    a category
  • the more features an object has, the more typical
    it is

29
Conceptual relationships
  • Concepts seem to be organised in systematic ways
  • Things higher up include the ones lower down

ANIMAL
MAMMAL
BIRD
SPARROW
CANARY
30
Hierarchical representations and inheritance
  • A node in a conceptual network inherits some
    properties from its superordinate
  • It can also add new properties of its own
  • It can override properties of the superordinate

Moves Eats breathes
ANIMAL
Flies Has feathers
BIRD
Does not fly
OSTRICH
31
Levels of conceptual representation
  • Rosch et al. 1976 propose 3 levels

Superordinate Or top level
FURNITURE
Basic level This is the level we tend to use and
think about
CHAIR
TABLE
Subordinate level Much more specific
ARMCHAIR
32
Properties of the basic level
  • The easiest to visualise
  • easier to imagine a CAR (basic) than a FIAT PUNTO
    (subordinate)
  • Used for neutral, everyday usage
  • were more likely to say thats a dog than
    thats a dachshund
  • Names of basic-level categories tend to be
    morphologically simple
  • Compare spoon vs. teaspoon, soup spoon

33
More properties of the basic level
  • high distinctiveness
  • maximally different from other categories
  • strong within-category resemblance
  • objects within the category resemble eachother
    more than they do objects outside the category
  • high informativeness
  • its more informative to say x is a dog than x
    is an animal
  • but in most cases, saying x is a dachshund is
    too specific

34
Final words on hierarchical representations
  • These are central to much work in semantics,
    psychology and Artificial Intelligence
  • E.g. The semantic web research in AI
  • Rather than just use google to find terms in web
    pages, wed like to make more intelligent
    queries Can you find me a car which is worth
    less than LM4000?
  • To do this, machines need a lot of knowledge
  • AI experts work with ontologies, which are
    essentially structured representations of
    knowledge
  • Hierarchical representations are fundamental
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