Dorota Klimek-Jankowska

The biggest challenge for computational linguists is to teach computers to interpet sentences. It is still a great puzzle for scientists to explain how human beings interpret sentences.

Semantics is the study of the meaning of linguistic expressions.

If we want to communicate successfully it is important that all linguistic

expressions mean the same to all language speakers.

Alice visits Humpty Dumpty HD: ‘There is glory for you’. A: ‘I don’t know what you mean by

‘glory’’HD: ‘Of course you don’t – till I tell

you. I meant ‘There is a nice knock-down argument for you!’

A: ‘But ‘glory doesn’t mean ‘a nice knock-down argument’

HD: ‘When I use a word, it means just what I choose it to mean – neither more nor less.’

A: ‘The question is whether you can make words mean so many different things.’

Do we all agree that what Humpty Dumpty says is ridiculous and non-sensical? Why?

A simple response is: you cannot make words mean so many different things to different speakers because we would not be able to understand each other while communicating.

Today we will ask a question of how it is possible that all language speakers are able to understand a never-ending list of still new sentences which they encounter in their every-day communication.

Probably there is something in our brain which allows us to interpret a never-ending list of novel sentences. This something is called SEMANTIC COMPETENCE.

The structure of today’s lecture:

I. What is semantic competence?

II. Approaches to meaning.

III. Semantic relations among words.

IV. The meaning of sentences.

V. Semantic relations involving sentences

VI. Lexical and structural ambiguity

I. WHAT IS SEMANTIC COMPETENCE?

The process of interpretation:

SPEAKER (produces a FORM)

HEARER (interprets the form i.e. translates FORM into MEANING)

SEMANTIC COMPETENCE: A speaker of a language is able to understand

sentences he/she has never heard before. We need a formal system which will help us understand how human being translate syntactic forms into meanings in their mind. This question is handled by the subfield of linguistics which is called:

SEMANTICS

II. APPROACHES TO MEANING

WHAT IS MEANING?

Sentence meaning (semantics) vs. speaker’s meaning (pragmatics)

Semantics is the study of literal, context-independent meaning of words and sentences.

Pragmatics is interested in what sentences mean in context, and is therefore concerned with utterance meaning.

The same sentence may be uttered in two different contexts

Scenario 1: Upon discovering your bike has a flat tire: That’s great!

Scenario2: Your friend has invited you to a party: That’s great!

The ‘mentalistic’ approach to meaning

The ‘mentalistic’ approach to meaning

claims that words primarily stand for

concepts, images, thoughts. This would

work for names like the Eiffel Tower or

even to common nouns such as bird, dog,

triangle or verbs walk, kick, laugh.

But is that it is rather difficult to apply it to

the meaning of such words as only, even, not, the, and, all, at most, more, always ….

The second drawback of the mentalistic approach to meaning is the following paradox:

If the meanings of words were just mental conepts, we would have problems understanding each other, because everybody can have different mental concepts evoked by particular linguistic expressions.

Consider the word ‘lecture’. Your mental concept of the word lecture

is one person standing in front of a blackboard and talking and it may also include the backs of the heads of your fellow students.

By contrast my mental concept related to this word is very different: for me it is an audience of students sitting in rows with puzzled faces. In spite of these differences in conceptualizing linguistic expressions, all speakers of a given language are able to understand one another without problems.

This means that meanings of linguistic expressions are not mental concepts, because we can have different mental concepts for different words.

The third drawback of the mentalistic approach to meaning is the fact that there are words for which we lack mental concepts e.g. wzdręga, oxygen, nitrogen but we are able to interpret these words.

The ‘referential’ approach to meaning

What else might be involved in a word’s meaning, besides a mental image.

Language is used to talk about things in the outside world. One well-known approach to semantics attempts to equate the meaning of a word or phrase with the entities to which it refers – its DENOTATION or REFERENTS.

Does the words: ‘pies’ mean the same to all of us? What does it mean and how is this meaning represented in formal semantics?

In the referential theory of meaning, the meaning of the word DOG is characterised as a set of individuals who are dogs in the actual world.

The set of individuals that a word picks out in the actual world is called its EXTENSION.

  QUESTION 5: Do you make a reference

to the external reality when you interpret these sentences?

 1) The students who are sitting on my left

have long hair.2) There are more male students in this

classroom than female ones.3) Not all windows are closed.

The intuition of external reference is something we want a semantic theory of natural language to capture.

We use language to talk about things outside.

The relation between linguistic expressions and things in the world is defined as a relation of reference, denotation or extension.

There are some words which do not have any extension (any referents in the actual world). These are for example: dragon, unicorn. The meaning of these words are concepts that they evoke which are called INTENSIONS.

SEMANTICS DECOMPOSITION

Still another approach to meaning postulates that we should decompose the meaning of words into features:

man

[+human, + male, + adult]

boy

[+human, + male, - adult]

woman

[+human, - male, + adult]

girl

[+human, - male, - adult]

This approach allows us to explain the anomaly of such sentences:

The table danced with Mary.

The subject lacks the feature [+animate]

The dog talked about John.

The subject lacks the feature [+human]

An adventage of this approach is that it allows us to group entities into classes

It also allows us to understand why for instance girl and woman are not synonyms. It is because synonyms must share all semantic features which is not the case about girl and woman. They differ by the feature +/- adult.

III. SEMANTIC RELATIONS AMONG WORDS

By virtue of meaning, words are able to enter into a variety of semantic relations with other words and phrases in the language.

SYNONYMS are words or expressions that have the same meaning in some or all contexts.

word 1

meaning 1

word 2

SYNONYMS

HOMONYMS: two different meanings that share spelling and pronunciation

meaning 1 word 1 meaning 2 bank - the institution which stores money

and a river bank

HOMOPHONES: different meanings and spelling but identical pronunciation

spelling 1 and meaning 1

pronunciation 1

spelling 2 and meaning 2

/naIt/ - knight, night

POLYSEMY: when the same form has twoclosely related meanings (not identical)

She gave her a diamond ring.His glass left a ring on the table.

They came to a fork in the road. He placed the fork beside the knife on the

table.

The sun is bright. – shiningJohn is a bright students. intelligent

ANTONYMS: are words or phrases that are opposites with respect to some component of their meaning.

There are different types of antonyms:

complementary antonymy: when one adjective is not applicable, the other one must be – there is no middle ground.

married vs. single

scalar antonyms also called gradable antonyms: where two words in a pair stand for the opposite ends of a scale:

hot vs. cold (scale of temperature)

big vs. small (scale of size)

tall vs. short (scale of height)

converse antonyms:

over – under

doctor – patient

buy – sell

It is possible to be neither over nor under.

When one member of this pair of antonyms

is not true the opposite is not necessarily

true.

HYPONYMS: words that are specific examples of some more general term e.g. a mouse is a hyponym of a rodent and a rodent is a hyponym of a mammal

IV. WHAT IS THE MEANING OF SENTENCES?

The circle is inside the square: When is this sentence true?

TRUTH CONDITIONS

When you know the meaning of a sentence you know its truth-conditions. You know which conditions need to be satisfied for the sentence to be true.

Look at sentences (1) – (2) and state intuitively what conditions need to be satisfied for those sentences to be interpreted as true.

1) All students who are sitting on my left have long hair 

Truth-conditions: this sentence is true iff all members of the set of individuals who have a property of being students sitting on my left belong to a set of individuals who have a property of having long hair.

2) Some male students in this classroom have wavy hair.

Truth-conditions: this sentence is true iff there exists at least one member of the set of male students in this classroom which belongs to the set of individuals who have a property of having wavy hair.

The Principle of Compositionality - the central principle of formal semantics

What is the meaning of sentences according to this principle?

The meaning of a complex expression is a function of the meanings of its parts and of the way they are syntactically combined.

How do we interpret the sentence ‘John is

happy’ in a compositional way?

 

Let me illustrate it step by step:

The meaning of ‘John’ is its referent: a particular individual whom the speaker has in mind and whose name is John.

John

The meaning of ‘be happy’ is a set of individuals who have a property of being happy.

be happy

What does John is happy mean according to the Principle of Compositionality?

We have to compose the meaning of ‘be happy’ and the meaning of ‘John’ :

While interpreting the sentence John is happy we check if it is true that John is a member of the reference set of ‘be happy’: John {Lisa, Kate, John}

V. SEMANTIC RELATIONS INVOLVING SENTENCES

PARAPHRASE: Two sentences that have the same meaning are said to be paraphrases of each other.

Examples:

The police chased the burglar.

The burglar was chased by the police.

 

I gave the ball to Chris.

I gave Chris the ball.

ENTAILMENT:

The relation in which the truth of one sentence

necessarily implies the truth of another.

Entailment can be symmetrical when a entails b and b entails a:

 Paul bought a car from Sue Sue sold a car to Paul.

Sue sold a car to Paul Paul bought a car from Sue

Entailment can be asymmetrical when a entails b but b does not entail a:

Rob is a man Rob is human.

Rob is human --/ Rob is a man.

CONTRADICTION:

When one sentence is true,

another sentence must be false:

 

Charles is single.

Charles is married.

VI. LEXICAL AND STRUCTURAL AMBIGUITY

Some sentences are ambiguous which means that they have two or more meanings.

There are two types of ambiguity:

Lexical ambiguity and structural ambiguity.

Lexical ambiguity

Fruit flies like banana.

 

flies: insects or an action of flying

 

Homonymy gives rise to the kind of ambiguity which called lexical ambiguity when a sentence can be interpreted in two different ways depending on which of two homonyms is chosen.

Structural ambiguity:

Sentences can be structurally ambiguous when the meanings of their component words can be combined in more than one way.

Inspector Gadget saw a mouse with glasses.