How do linguists study grammar?

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How do linguists study grammar?

• Lori Levin
• 11-721 Grammars and Lexicons
• August 29, 2007

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Outline

• Views of language
• Prescriptive
• Artistic
• Descriptive
• Claims about knowledge of a language
• Unconscious
• Complex
• Systematic
• Can be studied scientifically
• A research tool grammaticality judgments
• What is grammaticality?
• Problems with grammaticality
• Rationalism vs empiricism
• Why should language technologists care about
  grammaticality?

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Prescriptive and Descriptive Linguistics

• Natural phenomena cannot be legislated, just
  described.
• You cant declare the value of p to be 3.
• Sag, Wasow, and Bender, page 1
• Social phenomena can be legislated.
• Language use can be legislated as a social
  phenomenon, but it can also be studied as a
  natural phenomenon.

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Prescriptive view of language

• Rules about how language should be used
• Dont say Me and him went to the movies.
• It doesnt make sense because you cant say Me
  went to the movies.
• Focus on isolated phenomena that are thought to
  be corruptions of the language.
• Everybody should do their homework.
• Some people speak correctly and others dont.
• Rules are something that you are aware of.

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Artistic View of Language

• Language can be used creatively to make
  literature and poetry.
• Some people are better at it than others.
• Language is not systematic and rule governed.

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Descriptive view of language

• Study language as a natural phenomenon
• People say Me and him went to the movies.
• Thats interesting because they dont say Me went
  to the movies.
• Focus on all aspects of language, even very
  normal sentences.
• Every native speaker of a language speaks equally
  well.
• Unless there is an injury or an illness that
  affects certain parts of the brain or speech
  producing organs.
• Language consists of systematic knowledge that
  the speakers are not aware of.

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Outline

• Views of language
• Prescriptive
• Artistic
• Descriptive
• Claims about knowledge of a language
• Unconscious
• Complex
• Systematic
• Can be studied scientifically
• A research tool grammaticality judgments
• What is grammaticality?
• Problems with grammaticality
• Rationalism vs empiricism
• Why should language technologists care about
  grammaticality?

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Knowledge of Language

• Every normal speaker of any natural language has
  acquired an immensely rich and systematic body of
  unconscious knowledge, which can be investigated
  by consulting speakers intuitive judgments.
• Languages are objects of considerable
  complexity, which can be studied scientifically.
  That is, we can formulate hypotheses about
  linguistic structure and test them against the
  facts of particular languages.
• Sag et al., page 2

Claim 1
Claim 2
Claim 3
Claim 4
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Chomsky, 1957 on testable hypotheses

• The search for rigorous formulation in
  linguistics has a much more serious motivation
  than mere concern for logical niceties or the
  desire to purify well-established methods of
  linguistic analysis. Precisely constructed
  models for linguistic structure can play an
  important role, both negative and positive, in
  the process of discovery itself. By pushing a
  precise but inadequate formulation to an
  unacceptable conclusion, we can often expose the
  exact source of the inadequacy and, consequently,
  gain a deeper understanding of the linguistic
  data. More positively a formalized theory may
  automatically provide solutions for many problems
  other than those for which it was explicitly
  designed. Obscure and intuition-bound notions
  can neither lead to absurd conclusions nor
  provide new and correct ones, and hence they fail
  to be useful in two important respects.
• (Noam Chomsky has been the most influential
  linguist in many parts of the world since 1957.
  You may have also heard his name associated with
  politics. )

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Immensely rich and systematic body of
unconscious knowledge

• They saw Pat and Chris.
• They saw Pat with Chris.
• Who did they see Pat with?
• Who did they see Pat and?
• Has anyone ever had to tell you not to say this?

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Testable hypotheses about linguistic knowledge

• We like us.
• We like ourselves.
• She likes her. (She ? her)
• She likes herself.
• Nobody likes us.
• Leslie likes ourselves.
• Ourselves like us.
• Ourselves like ourselves.

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Testable hypotheses

• Use a reflexive pronoun only when
• Use a regular pronoun only when

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Counter-examples

• We think that Leslie likes us.
• We think that Leslie likes ourselves.
• We think that ourselves like Leslie.

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New Hypothesis

• Use a reflexive pronoun only when
• Use a regular pronoun only when
• (This is an English rule. Many languages do not
  follow it.)

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Support for the new hypothesis

• We think that she voted for her. (she ? her)
• We think that she voted for herself.
• We think that herself voted for her.
• We think that herself voted for herself.

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Counter-examples

• Our friends like us.
• Our friends like ourselves.
• Those pictures of us offended us.
• Those pictures of us offended ourselves.

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New Hypothesis

• Use a reflexive pronoun only when
• Use a regular pronoun only when

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Counter-examples

• Vote for us.
• Vote for ourselves.
• Vote for you.
• Vote for yourselves.

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Counter-examples

• We appealed to them to vote for themselves.
• We appealed to them to vote for them.
• Them ? them
• We appealed to them to vote for us.
• We appealed to them to vote for ourselves.

• We appeared to them to vote for themselves.
• We appeared to them to vote for them.
• Them them
• We appeared to them to vote for us.
• We appeared to them to vote for ourselves.

The theoretical machinery required for a viable
grammatical analysis could be quite abstract.
Sag et al., page 6
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Knowledge of Language

• Every normal speaker of any natural language has
  acquired an immensely rich and systematic body of
  unconscious knowledge, which can be investigated
  by consulting speakers intuitive judgments.
• Languages are objects of considerable
  complexity, which can be studied scientifically.
  That is, we can formulate hypotheses about
  linguistic structure and test them against the
  facts of particular languages.
• Sag et al., page 2

Claim 1
Claim 2
Claim 3
Claim 4
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Grammaticality Judgments as a scientific tool for
collecting data

• What is grammaticality?
• What are some problems in using it as a tool for
  collecting data?
• Grammaticality vs corpus analysis

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One more claim

• It is also possible to make testable hypotheses
  about how languages differ and what they have in
  common.

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Outline

• Views of language
• Prescriptive
• Artistic
• Descriptive
• Claims about knowledge of a language
• Unconscious
• Complex
• Systematic
• Can be studied scientifically
• A research tool grammaticality judgments
• What is grammaticality?
• Problems with grammaticality
• Rationalism vs empiricism
• Why should language technologists care about
  grammaticality?

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Investigate hypotheses by consulting native
speakers intuitions

• Many linguists (probably a majority) assume that
  people can distinguish strings of words that are
  sentences of their language from strings of words
  that are not sentences of their language.
• So imagine that you are a machine or a classifier
  that takes a sentence as input, and returns
  accept or reject as output.

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Native speakers as automata that accept and
reject strings of words.

• The student read a book.
• Student the a read book.

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Grammaticality

• A string of words that you recognize as a
  sentence in your native language is grammatical.
• A string of words that you do not recognize as a
  sentence in your native language is
  ungrammatical.
• When you decide whether a sentence is grammatical
  or ungrammatical, this is called giving a
  grammaticality judgment.
• Ungrammatical sentences are preceded by an
  asterisk or star (). Sometimes they are called
  starred sentences.
• If native speakers cant decide whether the
  sentence is grammatical or ungrammatical, it is
  preceded by a combination of stars and question
  marks.

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Grammaticality Descriptive

• When you give a grammaticality judgment, you are
  not supposed to judge whether the sentence is the
  most elegant or appropriate --- just whether it
  is a sentence of your language or not.
• You may have a stylistic preference for one of
  these, but they are all grammatical.
• These are things you never want to hear.
• These are things you want never to hear.
• These are things you want to never hear.

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Grammatical ? meaningful

• It is unlikely that Pat will succeed.
• It is improbable that Pat will succeed.
• Pat is unlikely to succeed.
• Pat is improbable to succeed.
• This could be meaningful, but most people
  consider it to be ungrammatical.
• They saw Pat with Chris.
• They saw Pat and Chris.
• Who did they see Pat with?
• Who did they see Pat and?
• Again, this could be meaningful, but it is
  ungrammatical.

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Syntactically well-formed vs semantically
well-formed

• Colorless green ideas sleep furiously.
• Syntactically well-formed
• Chomsky, 1957
• Colorless sleep green furiously ideas.
• Not syntactically well-formed

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Grammaticality Where to draw the line?

• Sentences that are understandable, but sound like
  mistakes are probably not grammatical.
• These are things that I dont know anyone who
  says.

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Where to draw the line?

• Sentences of bad poetry are not grammatical.
• Strange word order in order to make lines rhyme.
• Fame to our alma mater
• Thousands of voices ring
• Telling of love we bear her
• To her we laurels bring.
• From my high school song. Dont ask how I could
  remember something like that.
• indirect-object subject direct-object
  verb
• We bring laurels to her.
• subject verb direct-object
  indirect-object

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Grammaticality

• More bad poetry not grammatical
• Shout on high the ringing praises, loyal strong
  and true
• Bring we to our alma mater trust and
  honor due.
• verb subject indirect-object
  direct-object
• We bring trust and honor (that are) due
  to our alma mater.
• subject verb direct-object indirect-object

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Where to draw the line?

• However, many types of sentences that are found
  in writing, or are restricted to special contexts
  are considered to be grammatical and even have
  names
• Locative Inversion In this village live many
  people.
• Topicalization Sam, I like.
• Heavy NP Shift I presented to the students many
  examples of strange and unusual constructions.
  (indirect object comes before direct object
  because the direct object is too long)
• These are grammatical.

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Grammaticality

• Grammatical
• In this village live many people.
• I presented to the students many examples of
  strange and unusual constructions.
• Sam, I like.
• Not grammatical
• To her we laurels bring.
• Bring we to our alma mater trust and honor due.
• These are things that I dont know anyone who
  says.
• Who did they see Pat and?
• We told them to vote for ourselves.

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Problems with Grammaticality

• Dialect differences
• The car needs washed.
• (The car needs to be washed.)
• We go to the movies a lot anymore.
• (We go to the movies a lot these days.)
• I gave it her.
• (I gave it to her.)
• It were me what told her.
• (It was me that told her.)
• Mine is bigger than what yours is.
• (Mine is bigger than yours is.)
• Aint no chicken cant get into no coop.
• (No chicken can get into a coop.)
• (There isnt a chicken that can get into a coop.)

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Problems with grammaticality

• Changes over time
• (From Kroeger, Chapter 1)
• With two things hath God mens soul
  endowed.
• Normal word order in English before 1100 AD
• I know not what course others may take,
• Patrick Henry, 1775

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Grammaticality Discrete or Continuous?

• Manning (2003) Probabilistic Syntax
• We regard Kim to be an acceptable candidate.
• Consulting native speakers judgments.
• Conservatives argue that the Bible regards
  homosexuality to be a sin.
• Attested example.
• Kim turned out doing all the work.
• Consulting native speakers judgments.
• But it turned out having a greater impact than
  any of us dreamed.
• Attested example.
• Better to ask, How likely? than to ask,
  Possible or not?

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Philosophy LessonRationalism and Empiricism

• Rationalism the source of knowledge is reason
• Empiricism the source of knowledge is data

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Rationalist view of linguistic data

• Language is something in peoples minds a set
  of rules and principles that allows them to make
  grammaticality judgments and produce and
  understand sentences that they have never heard
  before
• i-language or internal language
• We study i-language asking people to give
  grammaticality judgments.
• A corpus (a collection of texts or speech) is
  e-language, or external language. It is not the
  object of study.

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Empiricist view of linguistic data

• Corpora are the objects of study.
• We study language by examining patterns in
  corpora (collections of texts or speech).

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Why do we need the philosophy lesson?

• In the second half of the 20th century,
  linguistics was heavily dominated by rationalism.
• Computational linguistics was also initially
  dominated by rationalism.
• Rationalism/empiricism was heavily debated in
  computational linguistics in the 1990s.
• Rationalism people writing grammar rules for a
  parser
• Empiricism statistical, corpus-based models
• In current Language Technologies Research,
  rationalism and empiricism are often combined.
• Combination A person choosing linguistic
  features as input to a machine learning
  algorithm, which then learns from the
  distribution of the features in a corpus.
• Combination Syntax-based statistical machine
  translation.
• Empiricism is gaining ground in linguistics
  (Manning 2003)
• Linguistics textbooks are still mainly
  rationalist.
• Empiricism is mentioned only in one footnote in
  Chapter 1 of the Sag et al book.
• But a few years earlier, it would not have been
  mentioned at all!

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Strong points of rationalism

• Infinite, creative capacity People can produce
  and understand sentences that have never been
  uttered before. They are not repeating memorized
  patterns, but applying productive rules.
• Leads people to wonder about things that dont
  exist in a corpus Who did you see Pat and?
• Probability is not grammaticality grammatical
  sentences may have very low probability.
• Probability reflects facts about the world, but
  grammaticality is independent of context.
• Clyde is an African elephant.
• Clyde is a pink elephant

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Strong points of empiricism

• Frequency of occurrence in a corpus is easier to
  measure reliably than a grammaticality judgment.
• Many ungrammatical sentences turn out to be
  acceptable in the right context.
• Identifying the right context turns out to be an
  interesting question that does not arise in the
  rationalist approach.
• Bresnan et al., 2005, 2007
• I gave her the book.
• I gave the book to her.

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Grammaticality in language technologies

• Real input (especially spoken input) is not
  always well-formed, so you should not build a
  program that accepts only grammatical sentences.
• Can we do away with grammar in language
  technologies?

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Grammaticality in Language Technologies

• You cannot extract the meaning of a sentence
  without processing the grammar
• Sue interviewed Sam.
• Sam interviewed Sue.
• LT output has to be comprehensible, and
  therefore, mostly grammatical
• Synthesized speech
• An automatically produced translation
• An automatically produced summary
• Error detection programs for computer-assisted
  language instruction or for word processing must
  distinguish grammatical from ungrammatical
  sentences.

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In favor of grammaticality

• Probability is not grammaticality grammatical
  sentences may have very low probability.
• Probability reflects facts about the world, but
  grammaticality is independent of context.
• Clyde is an African elephant.
• Clyde is a pink elephant