Transcript Dependency structure and cognition

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!
3
What Czech children do at school
blossomed out
by stream
kingcups
yellow
near
Jirka Hana & Barbora Hladká 2012
4
or even …
5
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
6
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
Gretta
Colin
John
Gaynor
me
Lucy
Peter
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C. Links are classified relations
relative
person
is-a
woman
man
parent
mother
child
father
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D. Nodes are richly related
Gretta
John
m
m s
Colin
f
f
s
b
s
s
b
w
me
h
Gaynor
d
gf
Lucy
s
Peter
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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
robin*
'flies'
penguin
'flies'
penguin*
'doesn't fly'
'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.
2.
3.
4.
5.
6.
Word-word dependencies are real.
'Deep' and 'surface' properties combine.
Mutual dependency is ok.
Dependents create new word tokens.
Extra word tokens allow raising.
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
But if a verb's subject is
a noun:
NP
VP
N
V
N
V
Cows
moo.
Cows
moo.
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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
A 'dominates' B
B
so A is above B
so B cannot 'dominate' A
B
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
?
mate
B*
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And in language …
word
LIKE-verb
like
I
?
NB like* is a
token of a token
subject
like*
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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
meaning
house
house
meaning
house
French
house*
meaning
French house
typical
house**
meaning
typical
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French house
Notation
house**
house*
typical
French
house
typical
French
house
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5. Extra word tokens allow raising.
subject
it
it
rains
subject
predicative
subject
it*
raining
keeps
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Raising in the grammar
A* is-a A, so A*
wins.
higher parent
A*
B
shared
lower parent
A
C
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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
Eine Concorde
higher parent
Eine Concorde*
gelandet
ist
hier
nie
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
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