Working with Discourse Representation Theory Patrick Blackburn & Johan Bos Lecture 4 Pronouns and Presupposition : Working with Discourse Representation Theory Patrick Blackburn & Johan Bos Lecture 4 Pronouns and Presupposition
Today : Today Pronouns
Anaphoric pronouns
Binding constraints
Presupposition
Triggers
Problems
Van der Sandt
Implementation
Slide3 : PRONOUNS
Pronouns : Pronouns We will concentrate on 3rd person singular personal pronouns in English:
he/him/himself
she/her/herself
it/itself
Anaphoric Pronouns : Anaphoric Pronouns We will focus on anaphoric pronouns
Anaphoric pronouns find their antecedent in the preceding text
Anaphora -- backwards Vincent looked at Mia. She dances.
Anaphoric Pronouns : Anaphoric Pronouns We will focus on anaphoric pronouns
Anaphoric pronouns find their antecedent in the preceeding text
Anaphora -- backwards Vincent looked at Mia. She dances.
She is the anaphor
Anaphoric Pronouns : Anaphoric Pronouns We will focus on anaphoric pronouns
Anaphoric pronouns find their antecedent in the preceeding text
Anaphora -- backwards Vincent looked at Mia. She dances.
Mia is the antecedent
Anaphoric Pronouns : Anaphoric Pronouns We will focus on anaphoric pronouns
Anaphoric pronouns find their antecedent in the preceeding text
Anaphora -- backwards Vincent looked at Mia. She dances.
How far backwards?
Cataphoric Pronouns : Cataphoric Pronouns We will not deal with cataphora
Cataphoric pronouns find their antecedent in the text following the pronoun
Example: After he lost the match, Butch left town.
Cataphoric Pronouns : Cataphoric Pronouns We will not deal with cataphora
Cataphoric pronouns find their antecedent in the text following the pronoun
Example: After he lost the match, Butch left town.
Deictic Pronouns : Deictic Pronouns Pronouns referring to objects in the situation, rather than linguistic objects
Examples: I, you, we, here, there, etc.
Pleonastic use of pronouns : Pleonastic use of pronouns Example: It’s about nine o’clock in the morning.
Grammatical agreement : Grammatical agreement In English, pronouns come with a gender and number feature
Only refer to antecedents carrying the same feature values:
he (singular, male):
men/boys, male animals
she (singular, female):
women/girls, female animals, things regarded as female, e.g. vehicles or ships
it (singular, neuter): things, animals, children
Pronouns and Ambiguity : Pronouns and Ambiguity Butch threw a TV at the window. It broke.
Butch threw a vase at the wall. It broke.
Pronouns and Ambiguity : Pronouns and Ambiguity Butch threw a TV at the window. It broke.
Butch threw a vase at the wall. It broke.
Pronouns and Ambiguity : Pronouns and Ambiguity Butch threw a TV at the window. It broke.
Butch threw a vase at the wall. It broke.
Pronouns and Ambiguity : Pronouns and Ambiguity Butch threw a TV at the window. It broke.
Butch threw a vase at the wall. It broke.
Pronouns and Ambiguity : Pronouns and Ambiguity Usually many candidate antecedents available
Example: Butch walks into his modest kitchen. He opens the refrigerator. He takes out a milk and drinks it.
Pronouns and Ambiguity : Pronouns and Ambiguity Usually many candidate antecedents available
Example: Butch walks into his modest kitchen. He opens the refrigerator. He takes out a milk and drinks it.
Pronouns and Ambiguity : Pronouns and Ambiguity Usually many candidate antecedents available
Example: Butch walks into his modest kitchen. He opens the refrigerator. He takes out a milk and drinks it.
Pronouns and Ambiguity : Pronouns and Ambiguity Usually many candidate antecedents available
Example: Butch walks into his modest kitchen. He opens the refrigerator. He takes out a milk and drinks it.
Pronouns and Ambiguity : Pronouns and Ambiguity Usually many candidate antecedents available
Example: Butch walks into his modest kitchen. He opens the refrigerator. He takes out a milk and shuts it.
Pronouns and Ambiguity : Pronouns and Ambiguity Usually many candidate antecedents available
Example: Butch walks into his modest kitchen. He opens the refrigerator. He takes out a milk and shuts it.
Pronouns and Ambiguity : Pronouns and Ambiguity Usually many candidate antecedents available
Example: Butch walks into his modest kitchen. He opens the refrigerator. He takes out a milk and shuts it.
Reflexive Pronouns : Reflexive Pronouns Examples:
Vincent goes to the toilet, and Jules enjoys himself.
Vincent enters the restaurant, and Jules watches him.
Reflexive Pronouns : Reflexive Pronouns Examples:
Vincent goes to the toilet, and Jules enjoys himself.
Vincent enters the restaurant, and Jules watches him.
Reflexive Pronouns : Reflexive Pronouns Examples:
Vincent goes to the toilet, and Jules enjoys himself.
Vincent enters the restaurant, and Jules watches him.
Binding rules : Binding rules Behaviour of pronouns: Butch likes himself. Butch likes him. Butch likes his chopper.
DRT and pronouns [1/3] : DRT and pronouns [1/3] Vincent did not dance with a woman. She …
DRT and pronouns [2/3] : DRT and pronouns [2/3] Vincent did with every woman. She …
DRT and pronouns [3/3] : DRT and pronouns [3/3] Vincent did with no woman. She …
Summing up : Summing up We have looked at anaphoric pronouns
It is unlikely that we can solve all the problems related to resolving pronouns
However, we can deal with some important aspects
Semantic constrains [gender]
Binding constrains [reflexivity]
DRT constrains pronoun resolution, but only partially
Slide33 : PRESUPPOSITION
Presupposition : Presupposition Presupposition vs. Entailment
Look at some examples of presupposition
Look at the typical problems associated with presuppositions
Concentrate on a DRT based approach due to Rob van der Sandt
What is presupposition? : What is presupposition? It is hard to pin down precisely what presuppositions are or how they behave
Presuppositions are a bit like entailment but not quite…
Entailment : Entailment Consider: Vincent has a car. A car is a vehicle.
This entails: Vincent has a vehicle.
Entailment : Entailment Consider: Vincent has a red car.
This entails: Vincent has a car.
Entailment and negation : Entailment and negation Entailments are typically not preserved under negation.
Entailment : Entailment Consider: Vincent has no car. A car is a vehicle.
This does not entail: Vincent has a vehicle.
Entailment : Entailment Consider: Vincent does not have a red car.
This does not entail: Vincent has a car.
Presupposition : Presupposition Consider: Vincent cleaned his car.
This entails: Vincent has a car.
Presupposition : Presupposition Consider: Vincent did not clean his car.
This entails: Vincent has a car.
Entailment or presupposition : Entailment or presupposition We call implications preserved under negation presuppositions
We call implications not preserved under negation entailments
Presupposition triggers : Presupposition triggers In English, presuppositions are usually triggered by lexical items
There are several tricks to find out whether a lexical item is a presupposition trigger or not
These tests are:
The negation test
The conditional test
The question test
Presupposition trigger test : Presupposition trigger test Consider the sentence: Alex is a bachelor.
This sentence implies that Alex is male.
But are we dealing with a presupposition or entailment?
Presupposition test : Presupposition test Alex is a bachelor. Does this presuppose: Alex is male?
Presupposition test : Presupposition test Alex is a bachelor. Does this presuppose: Alex is male?
Negation: Alex is not a bachelor. Implies: Alex is male? YES
Presupposition test : Presupposition test Alex is a bachelor. Does this presuppose: Alex is male?
Negation: Alex is not a bachelor. Implies: Alex is male? YES
Conditional: If Alex is a bachelor, then ... Implies: Alex is male? YES
Presupposition test : Presupposition test Alex is a bachelor. Does this presuppose: Alex is male?
Negation: Alex is not a bachelor. Implies: Alex is male? YES
Conditional: If Alex is a bachelor, then ... Implies: Alex is male? YES
Question: Is Alex is a bachelor? Implies: Alex is male? YES
Presupposition test : Presupposition test Alex is a bachelor. Does this presuppose: Alex is male?
Negation: Alex is not a bachelor. Implies: Alex is male? YES
Conditional: If Alex is a bachelor, then ... Implies: Alex is male? YES
Question: Is Alex is a bachelor? Implies: Alex is male? YES
Conclusion: being a bachelor presupposes being male.
Presupposition trigger test : Presupposition trigger test Consider the sentence: Alex is a man.
This sentence implies that Alex is male.
But are we dealing with a presupposition or entailment?
Presupposition test : Presupposition test Alex is a man. Does this presuppose: Alex is male?
Presupposition test : Presupposition test Alex is a man. Does this presuppose: Alex is male?
Negation: Alex is not a man. Implies: Alex is male? NO
Presupposition test : Presupposition test Alex is a man. Does this presuppose: Alex is male?
Negation: Alex is not a man. Implies: Alex is male? NO
Conditional: If Alex is a man, then ... Implies: Alex is male? NO
Presupposition test : Presupposition test Alex is a man. Does this presuppose: Alex is male?
Negation: Alex is not a man. Implies: Alex is male? NO
Conditional: If Alex is a man, then ... Implies: Alex is male? NO
Question: Is Alex is a man? Implies: Alex is male? NO
Presupposition test : Presupposition test Alex is a man. Does this presuppose: Alex is male?
Negation: Alex is not a man. Implies: Alex is male? NO
Conditional: If Alex is a man, then ... Implies: Alex is male? NO
Question: Is Alex is a man? Implies: Alex is male? NO
Conclusion: being a man does not presuppose being male.
Presupposition trigger test : Presupposition trigger test Consider the sentence: Butch knows that Zed is dead.
This sentence implies Zed is dead.
But are we dealing with a presupposition or entailment?
Presupposition test : Presupposition test Butch knows that Zed is dead. Does this presuppose: Zed is dead?
Presupposition test : Presupposition test Butch knows that Zed is dead. Does this presuppose: Zed is dead?
Negation: Butch does not know that Zed is dead. Implies: Zed is dead? YES
Presupposition test : Presupposition test Butch knows that Zed is dead. Does this presuppose: Zed is dead?
Negation: Butch does not know that Zed is dead. Implies: Zed is dead? YES
Conditional: If Butch knows that Zed is dead, then ... Implies: Zed is dead? YES
Presupposition test : Presupposition test Butch knows that Zed is dead. Does this presuppose: Zed is dead?
Negation: Butch does not know that Zed is dead. Implies: Zed is dead? YES
Conditional: If Butch knows that Zed is dead, then ... Implies: Zed is dead? YES
Question: Does Butch know that Zed is dead? Implies: Zed is dead? YES
Presupposition test : Presupposition test Butch knows that Zed is dead. Does this presuppose: Zed is dead?
Negation: Butch does not know that Zed is dead. Implies: Zed is dead? YES
Conditional: If Butch knows that Zed is dead, then ... Implies: Zed is dead? YES
Question: Does Butch know that Zed is dead? Implies: Zed is dead? YES
Conclusion: knowing P presupposes P.
Presupposition triggers : Presupposition triggers Presupposition triggers are not rare
English comes with a large variety of presupposition triggers
Possessives : Possessives Example: Mia likes her husband. Mia does not like her husband.
Presupposition: Mia has a husband.
To regret : To regret Example: Vincent regrets that he left Mia alone. Vincent does not regret that he left Mia alone.
Presupposition: Vincent left Mia alone.
To like : To like Example: Mia likes Vincent. Mia does not like Vincent.
Presupposition: Mia knows Vincent.
To answer : To answer Example: Butch answered the phone. Butch did not answer the phone.
Presupposition: The phone was ringing.
Only : Only Example: Only Jules likes big kahuna burgers. Not only Jules likes big kahuna burgers.
Presupposition: Jules likes big kahuna burgers.
Again : Again Example: Butch escaped again. Butch did not escape again.
Presupposition: Butch escaped once before.
To manage : To manage Example: Butch manage to start the chopper. Butch did not manage to start the chopper.
Presupposition: Butch had difficulties starting the chopper.
Third : Third Example: Butch lost for the third time. Butch did not loose for the third time.
Presupposition: Butch lost twice before.
Continue : Continue Example: Butch continued his race. Butch did not continue his race.
Presupposition: Butch interrupted his race.
To win : To win Example: Germany won the world cup. Germany did not win the world cup.
Presupposition: Germany participated in the world cup.
Another : Another Example: Peter wants another beer. Peter does not want another beer.
Presupposition: Peter had at least one beer.
To lie : To lie Example: Butch lied to Marsellus. Butch did not lie to Marsellus.
Presupposition: Butch told something to Marsellus.
Cleft construction : Cleft construction Example: It was Butch who killed Vincent. It was not Butch who killed Vincent.
Presupposition: Someone killed Vincent.
Proper names : Proper names Example: Butch talked to Marsellus. Butch did not talk to Marsellus.
Presupposition: There is someone named Marsellus.
Definite NP : Definite NP Example: Butch talked to the boss. Butch did not talk to the boss.
Presupposition: There is a boss.
Dealing with Presupposition : Dealing with Presupposition OK, so presuppositions are fairly common. But what`s the big deal?
Problems related to presupposition:
The Binding Problem
The Denial Problem
The Projection Problem
Presupposition may convey new information
Accommodation
The Binding Problem : The Binding Problem Example: Butch nearly escaped from his apartment.
Trigger “his apartment” presupposes that Butch has an apartment.
The Binding Problem : The Binding Problem Example: A boxer nearly escaped from his apartment.
Trigger “his apartment” presupposes that a boxer has an apartment.
But which boxer? A boxer? Any boxer?
The Denial Problem : The Denial Problem Vincent does not like his wife.
The Denial Problem : The Denial Problem Vincent does not like his wife.
Vincent does not like his wife, because Vincent does not have a wife!
The Denial Problem : The Denial Problem Vincent does not regret killing Zed, because he did not kill Zed!
The Denial Problem : The Denial Problem Vincent does not regret killing Zed, because he did not kill Zed!
Alex is not a bachelor, because she is a woman!
The Denial Problem : The Denial Problem Vincent does not regret killing Zed, because he did not kill Zed!
Alex is not a bachelor, because she is a woman!
Butch did not lie to Marsellus, because he did not tell him anything!
The Projection Problem : The Projection Problem Consider:
Mia’s husband is out of town.
Presupposes that Mia is married.
The Projection Problem : The Projection Problem Consider:
If Mia has a husband, then Mia’s husband is out of town.
Does NOT presuppose that Mia is married.
The Projection Problem : The Projection Problem Consider:
If Mia is married, then Mia’s husband is out of town.
Does NOT presuppose that Mia is married.
The Projection Problem : The Projection Problem Consider:
If Mia dates Vincent, then Mia’s husband is out of town.
Does presuppose that Mia is married.
The Projection Problem : The Projection Problem Complex sentences sometimes neutralise presuppositions
`Complex` meaning here sentences with conditionals, negation, or disjunction, modals
These sentences make it difficult to predict whether a presupposition projects or not
Accommodation : Accommodation Example: Vincent informed his boss.
Presupposition: Vincent has a boss.
What if we don’t have a clue whether Vincent has a boss or not?
Accommodation: incorporating missed information as long as this is not conflicting with other information
Solutions : Solutions There is a rich literature on presupposition
There are many different attempts to solve the problems related to presupposition
Many-valued logics
Default logics
Pragmatic theories
Non-monotonic reasoning
Van der Sandt’s Theory : Van der Sandt’s Theory Presuppositions are essentially extremely rich anaphoric pronouns
Presuppositions introduce new DRSs that need to be incorporated in the discourse context
It is a good way of dealing with the binding, projection, and denial problems
Van der Sandt’s Theory : Van der Sandt’s Theory Presuppositions introduce new DRSs that need to be incorporated in the discourse context
There are two ways to resolve presuppositional DRSs:
By binding
By accommodation
Two birds with one stone : Two birds with one stone The presupposition as anaphora theory handles anaphoric pronouns and presuppositions in essentially the same way Presupposition = Anaphora Anaphora = Presupposition
One mechanism : One mechanism Essentially one mechanism to deal with pronouns, proper names, definite descriptions, etc.
The differences are accounted for in the way they can accommodate and bind
Pronouns do not accommodate
Proper names always accommodate globally
Definite descriptions can accommodate anywhere
Presuppositions in DRT : Presuppositions in DRT We need to carry out two tasks:
Select presupposition triggers in the lexicon
Indicate what they presuppose
We will use a new operator, the alpha-operator,
If B1 and B2 are DRSs, the so is B1B2
B1 is the presupposition of B2
Preliminary DRSs : Preliminary DRSs She dances
Mia dances
The woman dances
Presupposition in the lexicon : Presupposition in the lexicon She
Mia
The woman
p@x λp. p@x λp. p@x λp.
Indefinite vs. Definite NP : Indefinite vs. Definite NP A woman
The woman
p@x λp. ; p@x λp.
The algorithm : The algorithm After constructing a preliminary DRS for an input sentences, we still have to resolve the presuppositions
After resolution we will have an ordinary DRS that we can use for our inference tasks
Resulting DRS needs to be consistent and informative
Binding Presuppositions : Binding Presuppositions Example: Vincent danced with a woman.
Binding Presuppositions : Binding Presuppositions Example: Vincent danced with a woman. The woman collapsed. ( )
Binding Presuppositions : Binding Presuppositions Example: Vincent danced with a woman. The woman collapsed. ; ( ( )) merge
Binding Presuppositions : Binding Presuppositions Example: Vincent danced with a woman. The woman collapsed. ; ( ( )) pick antecedent
Binding Presuppositions : Binding Presuppositions Example: Vincent danced with a woman. The woman collapsed. ; ( ) move
Binding Presuppositions : Binding Presuppositions Example: Vincent danced with a woman. The woman collapsed. merge reduction
Accommodating Presuppositions : Accommodating Presuppositions Example: If Mia dates Vincent, then her husband is out of town ( )
Global accommodation : Global accommodation Example: If Mia dates Vincent, then her husband is out of town ( )
Global Accommodation : Global Accommodation Example: If Mia dates Vincent, then her husband is out of town
Non-global accommodation : Non-global accommodation Performing global accommodation is saying that something is presupposed.
But recall the projection problem.
Presuppositions can be neutralised by binding and non-global accommodation.
Non-global Accommodation : Non-global Accommodation Example: If Mia is married, then her husband is out of town ( )
Non-global Accommodation : Non-global Accommodation Example: If Mia is married, then her husband is out of town ( )
Non-global Accommodation : Non-global Accommodation Example: If Mia is married, then her husband is out of town
Preferences : Preferences Binding is preferred to accommodation
Global accommodation is preferred to local accommodation
Van der Sandt’s Algorithm : Van der Sandt’s Algorithm Generate a DRS for the input sentence, with all elementary presuppositions marked by
Merge this DRS with the DRS of the discourse so far processed
Traverse the DRS, and on encountering an -DRS try to:
Bind the presupposed information to an accessible antecedent, or
Accommodate the information to a superordinated level of DRS
Remove those DRSs from the set of potential readings that violate the acceptability constraints
The acceptability constraints : The acceptability constraints DRSs should obey the binding rules
DRSs should not contain free variables
DRSs should be consistent and informative
DRSs should also be locally consistent and locally informative
Free Variable Check : Free Variable Check Consider the example: Every man likes his car
DRS obtained with global accommodation:
Free Variable Check : Free Variable Check Consider the example: Every man likes his car
DRS obtained with global accommodation:
Free Variable Check : Free Variable Check Consider the example: Every man likes his car
DRS obtained via intermediate accommodation:
Free Variable Check : Free Variable Check Consider the example: Every man likes his car
DRS obtained with local accommodation:
The projection problem solved : The projection problem solved Recall our example: If Mia is married, then her husband is out of town
Local constraints play a crucial role here!
The projection problem solved : The projection problem solved Recall our example: If Mia is married, then her husband is out of town
Local constraints play a crucial role here! Locally
uninformative
The projection problem solved : The projection problem solved Recall our example: If Mia is married, then her husband is out of town
Local constraints play a crucial role here! Locally
informative
Denial : Denial Example: Vincent does not like his dog. He does not have a dog!
The binding problem solved : The binding problem solved Example: A boxer nearly escaped from his apartment.
Preliminary DRS: ;( )) (
The binding problem solved : The binding problem solved Example: A boxer nearly escaped from his apartment.
Preliminary DRS: ;( )) ( Final DRS:
Proper Names : Proper Names Proper Names can be treated as presupposition triggers
Only global accommodation is permitted for proper names
This assures they will always end up in the global (outermost) DRS, accessible for subsequent pronouns
Proper Names : Proper Names Example: Every man knows Mia. She is Marsellus’ wife.
Proper Names : Proper Names Example: Every man knows Mia. She is Marsellus’ wife.
Implementation : Implementation The Curt system
Small fragment of English
Pronouns, presupposition triggers
Uses theorem prover
Bliksem
Uses model builder
Mace
Does all inference tasks