Linguistic TheoryLinguistic Theory

Lecture 2Lecture 2

Phrase StructurePhrase Structure

What was there before What was there before structure?structure?

• Classical studies:Classical studies:– Languages such as LatinLanguages such as Latin

•Rich morphologyRich morphology

•Not many word order restrictionsNot many word order restrictions– Mainly associated with meaningMainly associated with meaning– Words carried meaningWords carried meaning

•Therefore main emphasis on word form Therefore main emphasis on word form paradigms and meaning, but not much on paradigms and meaning, but not much on syntaxsyntax

• Traditional Grammar:Traditional Grammar:– Prescriptive: claimed Latin to be ‘pure’ Prescriptive: claimed Latin to be ‘pure’

language and all others were deviationslanguage and all others were deviations– Application of what was known about Application of what was known about

classical languages to modern classical languages to modern languageslanguages

– Thus, phenomena that were not similar Thus, phenomena that were not similar to Latin (word order restrictions) were to Latin (word order restrictions) were ignored or seen as ‘deviant’ignored or seen as ‘deviant’

• 1800s1800s– As early as the late 1500s similarities As early as the late 1500s similarities

between Indian and European languages between Indian and European languages had been notedhad been noted

– But the idea of an Indo-European family But the idea of an Indo-European family of languages did not become popular of languages did not become popular until the start of the 1800s. This was a until the start of the 1800s. This was a ‘new era’ for linguistics‘new era’ for linguistics

– Again the concentration was on classical Again the concentration was on classical languages (Greek, Latin, Sanskrit)languages (Greek, Latin, Sanskrit)

– Most easily accessible data concerned Most easily accessible data concerned word forms (phonology/morphology)word forms (phonology/morphology)

– Once more, syntax was not well studiedOnce more, syntax was not well studied

• In most of these approaches, the main In most of these approaches, the main aspects of syntactic description concerned aspects of syntactic description concerned grammatical functions (subject, object, etc.)grammatical functions (subject, object, etc.)

• In the languages being studied, In the languages being studied, grammatical functions were mainly grammatical functions were mainly indicated morphologically (Case, indicated morphologically (Case, agreement, etc.)agreement, etc.)

• Grammatical functions were defined Grammatical functions were defined semanticallysemantically– E.g. Subject = the one who performs the E.g. Subject = the one who performs the

action/what the sentence is aboutaction/what the sentence is about

• Therefore grammatical functions were Therefore grammatical functions were associated with words and no phrases were associated with words and no phrases were necessarynecessary

• Subordination of clauses was Subordination of clauses was recognisedrecognised– So the basis of constituent structure was So the basis of constituent structure was

available (one thing containing other available (one thing containing other things)things)

– But the need to extend this to non-But the need to extend this to non-clausal groups of words (phrases) didn’t clausal groups of words (phrases) didn’t seem to ariseseem to arise

StructuralismStructuralism

• Empiricist view + discovery procedures Empiricist view + discovery procedures = constituent structure analysis= constituent structure analysis

• Positive points:Positive points:– Could account for distributional patternsCould account for distributional patterns

• John/poor John left the roomJohn/poor John left the room

• I saw John/poor JohnI saw John/poor John

– Could account for the FACT of distributionCould account for the FACT of distribution

• Negative points:Negative points:– Was not formalised or made specific in Was not formalised or made specific in

terms of rules which constituted a terms of rules which constituted a grammargrammar•Such a grammar would be in the mind, Such a grammar would be in the mind,

which didn’t existwhich didn’t exist

– Therefore did not consider the issue of Therefore did not consider the issue of restricting grammatical theory to make restricting grammatical theory to make it more explanatoryit more explanatory•Why do phrases distribute the way they do?Why do phrases distribute the way they do?

– Linguistic RelativityLinguistic Relativity•Popular view of the structuralistsPopular view of the structuralists

•Each grammar could only be studied relative Each grammar could only be studied relative to itself – i.e. No commonalities between to itself – i.e. No commonalities between languages to compare themlanguages to compare them

– Supported by observation of Amerindian Supported by observation of Amerindian languageslanguages

•Therefore, in principle, languages could be Therefore, in principle, languages could be anyhowanyhow

•They were, more or less, an accident of the They were, more or less, an accident of the environment and culture they were set inenvironment and culture they were set in

• We determine what is a phrase in a We determine what is a phrase in a language on distributional groundslanguage on distributional grounds– But we cannot say why certain groups of But we cannot say why certain groups of

words are phrases because in principle any words are phrases because in principle any group of words could be a phrasegroup of words could be a phrase

– Description is easy:Description is easy:•The English gerund is an NP because it The English gerund is an NP because it

distributes like an NPdistributes like an NP– I don’t like [careful plans]/[carefully making plans]I don’t like [careful plans]/[carefully making plans]– [careful plans] are/[carefully making plans] is [careful plans] are/[carefully making plans] is

difficultdifficult

•But the gerund, unlike most NPs, contains no But the gerund, unlike most NPs, contains no obvious nounobvious noun

– [[NPNP [ [AdvAdv carefully] [ carefully] [V V making] [making] [NPNP plans]] plans]]

– Explanation is impossibleExplanation is impossible•Why do most NPs contain a noun?Why do most NPs contain a noun?•Why is [in the park] not an NP?Why is [in the park] not an NP?

• Why is a noun phrase a noun phrase?Why is a noun phrase a noun phrase?– Partly on distributional groundsPartly on distributional grounds

•NPs distribute the same as SOME nounsNPs distribute the same as SOME nouns

•But pronouns distribute like determiners and But pronouns distribute like determiners and NPs distribute like pronouns – so NPs NPs distribute like pronouns – so NPs distribute like SOME determiners!!!distribute like SOME determiners!!!

– From traditionFrom tradition•On the basis of semantic salience, On the basis of semantic salience,

traditional grammars took nouns to be traditional grammars took nouns to be grammatical functionsgrammatical functions

•Even though structuralists eschewed Even though structuralists eschewed meaning, it seems that they still took the meaning, it seems that they still took the classical position to heartclassical position to heart

• So why is a PP a PP?So why is a PP a PP?– The preposition is hardly the most The preposition is hardly the most

semantically salient part of a preposition semantically salient part of a preposition phrasephrase

– Distribution shows that they are not NPsDistribution shows that they are not NPs– What distinguishes them from NPs is that What distinguishes them from NPs is that

they contain a preposition, therefore we they contain a preposition, therefore we call them preposition phrasescall them preposition phrases

– This is not very consistentThis is not very consistent– But it doesn’t matter because there is no But it doesn’t matter because there is no

need for consistency as, in principle, need for consistency as, in principle, anything is possibleanything is possible

Chomsky and Phrase Chomsky and Phrase Structure GrammarStructure Grammar

• Change to rationalism and the study Change to rationalism and the study of language as knowledgeof language as knowledge

• We can only study internal language We can only study internal language by hypothesis testingby hypothesis testing

• Therefore we need grammatical Therefore we need grammatical hypotheses (= grammar) to be hypotheses (= grammar) to be explicitexplicit– Requires formalising rulesRequires formalising rules

• Phrase Structure RulesPhrase Structure Rules– E.g.: VP E.g.: VP V NP V NP– A list of such rules = Phrase Structure A list of such rules = Phrase Structure

GrammarGrammar– A PSG produces a set of Phrase Markers A PSG produces a set of Phrase Markers

(tree diagrams)(tree diagrams)– Still nothing wrong with:Still nothing wrong with:

•NP NP Adv V NP Adv V NP

•So still unconstrained = not explanatorySo still unconstrained = not explanatory

– But ...But ...

• Formalising PS rules helped to:Formalising PS rules helped to:– Point out problems with basic Immediate Point out problems with basic Immediate

Constituent Analysis to show that more Constituent Analysis to show that more is needed to account for human is needed to account for human languageslanguages

– Further our understanding of rule Further our understanding of rule systems and to suggest what is needed systems and to suggest what is needed to capture natural language datato capture natural language data

• Problems for IC analysis: E.g. The Problems for IC analysis: E.g. The passivepassive– We might analyse a passive sentence thus:We might analyse a passive sentence thus:

• SS

NP VP NP VP

John VerbJohn Verb

Aux V Aux V

was liked was liked

•This is easy to do with PS rulesThis is easy to do with PS rules

•But...But...

• This analysis fails to capture certain This analysis fails to capture certain facts:facts:– Only transitive verbs can appear in the Only transitive verbs can appear in the

passive:passive:– He was likedHe was liked– * he was smiled* he was smiled

•Transitive verbs are usually restricted to VPs Transitive verbs are usually restricted to VPs which contain objects:which contain objects:

– They liked JohnThey liked John– * they liked* they liked

• Intransitives are restricted to VPs without an Intransitives are restricted to VPs without an objectobject

– He smiledHe smiled– * he smiled them* he smiled them

•So in the passive, things are turned upside downSo in the passive, things are turned upside down•Why?Why?

– Verbs place semantic restrictions on Verbs place semantic restrictions on their subjects and objectstheir subjects and objects

– John hates insincerityJohn hates insincerity– * insincerity hates John* insincerity hates John– Insincerity worries JohnInsincerity worries John– *John worries insincerity*John worries insincerity

Hate Hate animate/sentient subject animate/sentient subject Worry Worry animate/sentient object animate/sentient object

• In the passive these restrictions are In the passive these restrictions are reversed:reversed:

– Insincerity was hated (by John)Insincerity was hated (by John)– *John was hated (by insincerity)*John was hated (by insincerity)– John was worried (by insincerity)John was worried (by insincerity)– * insincerity was worried (by John)* insincerity was worried (by John)

•A phrase structure analysis cannot account A phrase structure analysis cannot account for these observationsfor these observations

• Mathematical LinguisticsMathematical Linguistics– Formalising rules for phrase structure Formalising rules for phrase structure

using re-write rules enabled Chomsky to using re-write rules enabled Chomsky to explore aspects of grammar that had explore aspects of grammar that had never been thought of beforenever been thought of before

– Rule a) produces structure B):Rule a) produces structure B):•a)a) X X Y Z Y Z B)B) X X

Y ZY Z

– But what does rule b) produce?But what does rule b) produce?•b)b) W X W X Y Z Y Z

– Such rules produce structures which Such rules produce structures which cannot be represented by a tree diagramcannot be represented by a tree diagram

– Phrase Structure Grammar: rules can have Phrase Structure Grammar: rules can have only one element to the left of the arrowonly one element to the left of the arrow

– Unrestricted Re-write System: rules can Unrestricted Re-write System: rules can have more than one element to the left of have more than one element to the left of the arrowthe arrow

– Note that a PSG is a (restricted) kind of Note that a PSG is a (restricted) kind of URSURS

– So, any language that a PSG can generate, So, any language that a PSG can generate, a URS can too. But not vice versaa URS can too. But not vice versa

– URS languagesURS languages

PSG languagesPSG languages

• There are grammars which are more restrictive There are grammars which are more restrictive than URSs but less restrictive than simple PSGs:than URSs but less restrictive than simple PSGs:– A X A X A Y Z A Y Z

• This rule rewrites X, when it is preceded by AThis rule rewrites X, when it is preceded by A• The rule is ‘context sensitive’The rule is ‘context sensitive’

• A context sensitive rule is a kind of unrestricted A context sensitive rule is a kind of unrestricted rewrite rule where only one element on the left of rewrite rule where only one element on the left of the arrow is rewrittenthe arrow is rewritten

• A context free rule is a kind of context sensitive A context free rule is a kind of context sensitive rule with no context statedrule with no context stated

• So:So: unrestricted rewrite grammar unrestricted rewrite grammar

context sensitive PS grammar context sensitive PS grammar

context free PS grammar context free PS grammar

• The question is: what kind of The question is: what kind of grammar is human grammar?grammar is human grammar?– This could be a way of restricting This could be a way of restricting

linguistic hypotheses and making them linguistic hypotheses and making them more explanatorymore explanatory

– Most linguists think that the phrase Most linguists think that the phrase structure part of human grammar is no structure part of human grammar is no more complex than a context free more complex than a context free rewrite systemrewrite system

– Though all agree that this is not enough Though all agree that this is not enough to account entirely for all grammatical to account entirely for all grammatical phenomenaphenomena

More restrictionsMore restrictions

• Phrase structure grammars (even Phrase structure grammars (even context sensitive ones) still allow things context sensitive ones) still allow things that we don’t find in human languages:that we don’t find in human languages:– PP PP Adv V Adv V

• Phrases have headsPhrases have heads• There is no way to represent the notion There is no way to represent the notion

of the head in a standard rewrite rule of the head in a standard rewrite rule because what is on the left of the arrow because what is on the left of the arrow is not connected to what is on the rightis not connected to what is on the right– X X Y Z Y Z

• In 1970 Chomsky proposed a In 1970 Chomsky proposed a restriction on rewrite rules which restriction on rewrite rules which addressed this problemaddressed this problem

• X-bar theory:X-bar theory:– XXnn ... X ... Xmm ... (ignore ... (ignore nn and and mm))– Rules are restricted to the type where Rules are restricted to the type where

there must be an element to the right of there must be an element to the right of the arrow which is the same category as the arrow which is the same category as the one on the leftthe one on the left

– X-bar grammars do not form a subset of X-bar grammars do not form a subset of any of the types in the Chomsky any of the types in the Chomsky hierarchyhierarchy•So perhaps mathematical types are not so So perhaps mathematical types are not so

useful afterall!useful afterall!

Generalised Phrase Generalised Phrase Structure GrammarStructure Grammar

• Some argued that Chomsky was Some argued that Chomsky was wrong about the limitations of wrong about the limitations of context free PSGscontext free PSGs

• The problem Chomsky pointed out The problem Chomsky pointed out was that elements often appear in was that elements often appear in one position when we would expect one position when we would expect them to be in another (e.g. Passive)them to be in another (e.g. Passive)

• But we can overcome this problem if we But we can overcome this problem if we allow a new kind of category:allow a new kind of category:– X/Y X/Y

•Called a ‘slash’ categoryCalled a ‘slash’ category•Means an X which lacks a YMeans an X which lacks a Y

• SS

NP S/NP NP S/NP

who NP VP/NPwho NP VP/NP

John V NP/NP John V NP/NP

met met

• Rules needed:Rules needed:– X/X X/X basic rulebasic rule– Y/X Y/X ... Z/X .. ... Z/X .. inheritance ruleinheritance rule– Y Y X Z/X X Z/X resolution ruleresolution rule