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Dependency structure and cognition

Richard Hudson

Depling2013, Prague

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The question• What is syntactic structure like?

– Does it include dependencies between words (dependency structure)?

– Or does it only contain part-whole links (phrase structure)?

She looked after him

after him

She looked after him

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Relevant evidence: familiarity

• University courses teach only one approach.

• School grammar sometimes offers one.– Usually dependency structure– even in the USA

• Reed-Kellogg sentence-diagramming

– especially in Europe– and especially in the Czech Republic!

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What Czech children do at school

blossomed out kingcups

by stream

near

yellow

Jirka Hana & Barbora Hladká 2012

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or even …

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Relevant evidence: convenience

• Dependency structure is popular in computational linguistics.

• Maybe because of its simplicity:– few nodes– little but orthographic words

• Good for lexical cooccurrence relations

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Relevant evidence: cognition

• Language competence is memory

• Language processing is thinking

• Memory and thinking are part of cognition

• So what do we know about cognition?

• A. Very generally, cognition is not simple– so maybe syntactic structures aren't in fact

simple?

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B. Knowledge is a network

me Gaynor

Lucy

Peter

JohnGretta

Colin

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C. Links are classified relationsperson

woman man

relative

parent child

mother father

is-a

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D. Nodes are richly related

me Gaynor

Lucy

Peter

JohnGretta

Colin

m

s

mf f

d

gf

bb

wh

s ss

s

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E. Is-a allows default inheritance

• Is-a forms taxonomies.– e.g. 'linguist is-a person', 'Dick is-a linguist'

• Properties 'inherit' down a taxonomy.

• But only 'by default' – exceptions are ok.– e.g. birds (normally) fly– but penguins don't.

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Penguins

bird

robin

'flies'

penguin 'doesn't fly'

robin* 'flies' penguin* 'doesn't fly'

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Cognitivism

• 'Cognitivism'– 'Language is an example of ordinary cognition'

• So all our general cognitive abilities are available for language– and we have no special language abilities.

• Cognitivism matters for linguistic theory.

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Some consequences of cognitivism

1. Word-word dependencies are real.

2. 'Deep' and 'surface' properties combine.

3. Mutual dependency is ok.

4. Dependents create new word tokens.

5. Extra word tokens allow raising.

6. But lowering may be ok too.

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1. Word-word dependencies are real

• Do word-word dependencies exist (in our minds)?– Why not? – Compare social relations between individuals.

• What about phrases?– Why not? – But maybe only their boundaries are relevant?– They're not classified, so no unary branching.

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Punctuation marks boundaries

• At the end of the road, turn right.

• Not:– At the end of the, road turn right.– At the end, of the road turn right.– At the end of the road turn right,

• How do we learn to punctuate if we can't recognise boundaries?

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No unary branching

• If S NP + VP, then:

S

NP VP

N V

Cows moo. Cows moo.

N V

But if a verb's subject is a noun:

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2. 'Deep' and 'surface' properties combine.

• Dependencies are relational concepts.• Concepts record bundles of properties that

tend to coincide– e.g. 'bird': beak, flying, feathers, two legs, eggs– 'mother': bearer, carer

• So one dependency has many properties:– semantic, syntactic, morphosyntactic– e.g. 'subject' ….

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'subject'

The typical subject is defined by• meaning

– typically 'actor' or …

• word order and/or case– typically before verb and/or nominative

• agreement– typically the verb agrees with it

• status– obligatory or optional, according to finiteness

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So …

• Cognition suggests that 'deep' and 'surface' properties should be combined– not separated

• They are in harmony by default– but exceptionally they may be out of harmony– this is allowed by default inheritance

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3. Mutual dependency is ok.

• Mutual dependency is formally impossible in standard notation

• And is formally impossible in phrase structure theory

• So if it exists, we need to – resist PS theory– change the standard notation

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Mutual dependency exists

• I wonder who came?

• Who is subject of came, – so who depends on came.

• But who depends on wonder

• and came can be omitted:– e.g. Someone came – I wonder who.

• So came depends on who.

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Standard notation

A

B

B

A

A 'dominates' B

so A is above B

so B cannot 'dominate' A

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4. Dependents create new word tokens.

• General cognition: – every exemplar needs a mental node.– no node carries contradictory properties.– so some exemplars need two nodes.

• E.g. when we re-classify things.– NB we can remember both classifications

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What kind of bird?

bird

blackbird

B

B*

?mate

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And in language …

word

LIKE-verb

like

?subject

I

like*NB like* is a

token of a token

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The effect of a dependent

• When we recognise a dependent for W, we change W into a new token W*.

• The classification of W* may change.• W* also has a new meaning

– normally a hyponym of W– but may be idiomatic

• If we add dependents singly, this gives a kind of phrase structure!

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typical French house

HOUSE housemeaning

house

house*

house**

French

housemeaning

French housemeaning

typicalFrench house

meaningtypical

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Notation

houseFrenchtypical

house*

house**

houseFrenchtypical

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5. Extra word tokens allow raising.

rainssubjectit

keepsit* raining

subjectit

subject predicative

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Raising in the grammar

A

A*

C

B

higher parent

lower parent

shared

A* is-a A, so A* wins.

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6. But lowering may be ok too.

• Raising is helpful for processing– the higher parent is nearer to the sentence root.

• But sometimes lowering is helpful too– e.g. if it allows a new meaning-unit.

• Eine Concorde gelandet ist hier nie.

a Concorde landed has here never.

A-Concorde-landing has never happened here.

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German Partial VP fronting

gelandet ist hier nie

Eine Concorde

Eine Concorde*

higher parent

lower parent

lowered

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Conclusions

• Language is just part of cognition.• So syntactic dependencies are:

– psychologically real– rich (combining 'deep' and 'surface' properties)– complex (e.g. mutual, multiple).

• And dependency combines with – default inheritance– multiple tokens