Governing Category and Coreference

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# Governing Category and Coreference - PowerPoint PPT Presentation

Governing Category and Coreference. Dekang Lin Department of Computing Science University of Alberta. Constraints on Coreference Relationships. John hurt himself *Miss Marple hurt himself John likes him John said Peter likes him She likes Susan She said Jan likes Susan. C-command.

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### Governing Category and Coreference

Dekang Lin

Department of Computing Science

University of Alberta

Constraints on Coreference Relationships
• John hurt himself
• *Miss Marple hurt himself
• John likes him
• John said Peter likes him
• She likes Susan
• She said Jan likes Susan
C-command
• C-command is a relationship between two nodes in a parse tree
• c-commands if

1.  does not dominate 

2. the parent of  dominates 

• dominates if  is an ancestor of  in the parse tree

NP

Det

N’

a

N

PP

forecast

P

NP

of

AP

N

returns

A

future

Binding
• A noun phrase  is bound to another noun phrase  if
•  and  are co-indexed (refer to the same entity)
•  c-commands .
• Examples
• John hurt himself
• John likes him
• John said Peter likes him
• She likes Susan
• She said Jan likes Susan
Classification of NPs
• NPs can be classified into the following categories according to their binding property:
• R-Expressions: Mary, the policeman, the company
• Pronominals: he, she, you, her, his, ...
• Reciprocals and reflexives: each other, himself, herself, ...
• Chomsky82:

-anaphor +anaphor

-pronominal R-expressions Refl/Recp

+pronominal Pronominals PRO

Binding Theory
• Tentative Definition: The local domain of phrase is the smallest clause that contains the phrase.
• Principle A: A NP with [+anaphor] must be bound within its local domain.
• Principle B: A NP with [+pronominal] must not be bound within its local domain.
• Principle C: A NP with [-anaphor -pronominal] must not be bound.
Examples
• John hurt himself
• John likes him
• John said Peter likes him
• She likes Susan
• She said Jan likes Susan
• *John thinks that himself is the best candidate
• John considered himself to be the best candidate
• John said that pictures of himself were on sale.
• *John wanted Mary to take a picture of himself.
Government
• Government is a relationship between two nodes in a parse tree.
•  governs  if
• 1.  is the head of a phrase and a potential governor
• 2. A phrase headed by  dominates 
• 3. There does not exist a g such at g governs  and  governs g
• Potential governors
• All lexical categories: N, V, A, P
Binding Theory (Revised)
• The governing category of  is the minimal phrase that contains , the governor of , and a subject (a NP at spec of an IP or a NP) that c-commands the governor.
• Binding Theory
• Principle A: A NP with [+anaphor] must be bound within its governing category.
• Principle B: A NP with [+pronominal] must not be bound within its governing category.
• Principle C: A NP with [-anaphor -pronominal] must not be bound.
Example 1
• John likes himself
Example 2
• Mary likes John’s picture of himself
Example 3
• *John wanted Mary to take a picture of himself
Example 4
• John considers himself to be the best
Example 5
• John said that pictures of himself were on sale
Example 6
• *Mary believes herself can afford the car
Binding and PRO
• PRO is treated like lexical NPs
• John persuaded Maryi PROi to defend herself/*himself
• Johni promised Mary PROi to defend himself/*herself
Problem Cases
• They knew/found that each other’s photos were on sale
• Mary believes it is possible for herself to win
• Jill knew that nothing could obliterate the memory of those photographs of herself [Napoli93]
• Ralph considers Mary inferior to himself [Napoli93, p.519]
• ?Ralph considers John inferior to himself
Local Domain (Revisted Again)
• The Local Domain of  is the minimal phrase that contains  , its governor, and a subject (a NP at spec of an IP or a NP) that c-commands the governor and is accessible to .
Non-referential NPs
• Some NPs, such as nothing, there, it (expletive), are not accessible to anything.
Each Other’s
• “Each other’s” is not accessible to “each other’s”
A Singular Nouns is not Accessible to “Each Other”
• Pollard&Sag 94, p.245
• John and Mary know that the journal had rejected each other’s papers
• Why are John and Mary letting the honey drip on each other’s feet [Chomsky 1973: 261]
• John suggested that tiny gilt-framed portraits of each other would make ideal gifts for the twins
• The agreement that Iran and Iraq reached guaranteed each other’s trading rights in the disputed waters until the year 2010
Inaccessibility between Argumentsof a Predicate
• If two arguments of a predicate are known to be distinct a priori, they are not accessible to each other.
• Ralph considers Mary inferior to himself [Napoli93, p.519]
• *Ralph considers Mary fond of himself [Napoli93, p.519]
Accessibility
• A is inaccessible to B if, disregarding agreement features, A could not possibly bind B.
• Otherwise, A is accessible to B
Exceptions to Principle B
• Example
• Jill took her brother with her to the market [Napoli93,513]
• The use of “her” instead of “herself” may be explained by Full Interpretation
• “X took Y with Z” implies Z=X.
• the only purpose to use an anaphor as Z is to indicate Z=X
Exceptions to Principle C
• ABC applauded the new contract, which gave the network more flexibility.
• The company said it plans to use the sale proceeds to invest in business opportunities more closely identified with the company’s “refocused direction.”
Anaphors without Governing Category
• Not all anaphors have governing categories:
• A letter from Mary about herself was in the mail [Kuno93, p.138]
• Those nude pictures of himself ruined John’s career. [Napoli93, p550]
• RevisedPrinciple A:
• If an anaphor has a governing category, it must be bound within its governing category.
• If an anaphor has no governing category, it must be co-indexed with the most accessible NP in the context.
Examples of Anaphor without GC
• The picture of himselfi in Newsweek bothered Johni
• *The picture of himselfi in Newsweek bothered John’si father
• The picture of himselfi in Newsweek dominated John’si thoughts
• The picture of himselfi in Newsweek shattered the piece of mind that Johni had spent the last six months trying to restore.
Conclusion
• We proposed a definition of Governing Category that is simpler and has better empirical coverage than Chomsky’s earlier definition.
Unresolved Problems
• John made sure it was clear to Mary that the picture of himself was already sold
• Mary made sure it was clear to John that the picture of himself was already sold
• Bill suspected the silence meant that a picture of himself would soon be on the post office wall [Pollard&Sag94, p.268]
Problems with C-command
• Pollard&Sag94 pointed out the following problems
• Mary talked to John about himself
• *Mary talked to himi about Johni
• Possible solution
• redefine c-command so that prepositions do not block c-command
• introduce linear order requirement in c-command