Anaphora The basics

Keywords Cohesion Anaphora Anaphor Antecedent Anaphora resolution Coreference Coreferential Pronominal anaphora Lexical NP anaphora Intrasentential and intersentential Location of the antecedents Cataphora Anaphora and deixis

Outline of the lecture Basic notions and terminology Coreference Varieties of anaphora according to the form of the anaphor Types of anapha according to the locations of the anaphor and the antecedent Indirect anaphora Location of the antecedent Anaphora and cataphora

Basic notions and terminology (1) Cohesion is a phenomenon accounting for the observation (and assumption) that what people try to communicate in spoken or written form under ‘normal circumstances’ is a coherent whole, rather than a collection of isolated or unrelated sentences, phrases or words Sipping the last of the bitter cordial, the businessman was presented with the cheque. A look of incredulity crept over his face. Sipping the last of the bitter cordial, the businessman was presented with the cheque. A look of incredulity crept over her face. Sipping the last of the bitter cordial, the businessman was presented with the cheque. This lecture is about anaphora.

Definition of cohesion Cohesion in English [1976]--cohesion is a semantic concept that 'occurs when the interpretation of some element in the discourse is dependent on that of another' (4). . . . At its simplest, cohesion refers to the ways in which texts are 'stuck together'--the ways in which sentences are linked or connected by various linguistic and semantic ties."

Basic notions and terminology (2) Anaphora (Haliday & Hasan 76): cohesion which points back to some previous item Pointing back, NOT referring! Anaphor: the "pointing back" word Antecedent: the entity to which it refers or for which it stands   Anaphora resolution: the process of determining the antecedent of an anaphor

Anaphora: The use of a linguistic unit, such as a pronoun, to refer back to another unit, as the use of her to refer to Anne in the sentence Anne asked Edward to pass her the salt. Anaphora represents the relation between a “proform” (called an “anaphor”) and another term (called an "antecedent"), when the interpretation of the anaphor is in a certain way determined by the interpretation of the antecedent. Barbara Lust, Introduction to Studies in the Acquisition of Anaphora, D. Reidel, 1986

Basic notions and terminology (3) Coreference: the act of picking out the same referent in the real world. Anaphors and antecedents are said to be coreferential if they have the same referent in the real world

Example Sophia Loren says she will always be grateful to Bono. The actress revealed that the U2 singer helped her calm down when she became scared by a thunderstorm while travelling on a plane. Coreferential chains: {Sophia Loren, she, the actress, her, she}, {Bono, the U2 singer}, {a thunderstorm}, {a plane}

Coreference and anaphora Not all types of anaphora involve coreference! Identity-of-sense anaphora: The man who gave his paycheck to his wife was wiser that the man who gave it to his mistress Verb anaphora: Stephanie balked, as did Mike Bound anaphora: Every man has his own agenda

Substitution test to establish coreference John has his own agenda John has John’s own agenda Every man has his own agenda. Every man has every man’s own agenda. ??

Varieties of anaphora according to the form of the anaphor Nominal anaphora arises when a referring expression (pronoun, definite noun phrase or proper name), has a non-pronominal noun phrase as its antecedent. Nominal anaphora: most important and frequently occurring class of anaphora researched and covered most extensively, and best understood in the Computational Linguistics literature.

Varieties of anaphora according to the form of the anaphor (2) Pronominal anaphora: the most widespread type of anaphora Personal pronouns: John had to go to a meeting so he decided to have a shave Possessive pronouns: John grabbed his old razor Reflexive pronouns...but unfortunately cut himself during the shave Demonstrative pronouns: This delayed him further... John picked the electric razor. That was not working either Relative pronouns: John picked the electric razor which was not working either).

Varieties of anaphora according to the form of the anaphor (3) Lexical noun phrase anaphora: realised syntactically as definite noun phrases, also called definite descriptions, and proper names. Roy Keane has warned Manchester United he may snub their pay deal. United's skipper is even hinting that unless the future Old Trafford Package meets his demands, he could quit the club in June 2000. Irishman Keane, 27, still has 17 months to run on his current £23,000-a-week contract and wants to commit himself to United for life. Alex Ferguson's No. 1 player confirmed: ‘If it's not the contract I want, I won't sign’

Lexical noun phrase anaphors: further examples Mark went for a drive and got hopelessly lost. That's Mark for you. Both noses went down to the footprints in the snow. These footprints were very fresh.

Most crucial (and most studied) type of anaphora in NLP identity-of-reference nominal anaphora: involves coreference by virtue of the anaphor and its antecedent having the same real-world referent

Zero anaphora Zero anaphors are ‘invisible' anaphors Zero pronominal anaphora occurs when the anaphoric pronoun is omitted but  is nevertheless understood Willie paled and  pulled the sock up quickly Marta está muy cansada.  Ha estado trabajando todo el día.

Anaphoric / non-anaphoric Are pronouns always anaphoric? Pleonastic it: It is important, It is necessary, It is far away, It is raining…. Generic use of pronouns: He that plants thorns must never expect to gather roses. Are definite descriptions always anaphoric? Generic definite descriptions:No one knows precisely when the wheel was invented

Types of anaphora according to the locations of the anaphor and the antecedent intrasentential : anaphor and its antecedent are located in the same sentence. intersentential : antecedent is in a different (preceding) sentence from the anaphor Pop superstar Robbie Williams hid his secret heartbreak as he picked up three Brit awards last night. He was stunned to discover that his ex-fiancée, All Saints beauty Nicole Appleton, is dating a New York rapper. Robbie, 25, was distraught after being dumped by the love of his life Nicole at Christmas.

Indirect anaphora (bridging, associative anaphora) Indirect anaphora: arises when a reference becomes part of the hearer’s or reader’s knowledge indirectly rather than by direct mention: Although the store had only just opened, the food hall was busy and there were long queues at the tills. When Take That broke up, the critics gave Robbie Williams no chance of success.

Location of the antecedent Pronominal anaphors: distance between a pronominal anaphor and its antecedent in most cases does not exceed 2-3 sentences Demonstrative anaphors: longer-distance anaphors than pronouns Definite descriptions: longer-distance Proper names: even longer-distance anaphors

What is cataphora The use of a linguistic unit, such as a pronoun, to refer ahead to another unit, for example, the use of him to refer to John in the sentence Near him, John saw a snake. Cataphora is the coreference of one expression with another expression which follows it. The following expression provides the information necessary for interpretation of the preceding one.  

An example In the following sentence, the relationship of one to a towel is an example of cataphora: If you need one, there’s a towel in the top drawer.

Cataphora Cataphora arises when a reference is made to an entity mentioned subsequently in the text.  She is now as famous as her ex-boyfriend. From the deserts of Kazakhstan to the south seas of Tonga, everyone knows Monica Lewinsky

Endophora Endophora is coreference of an expression with another expression either before it or after it. One expression provides the information necessary to interpret the other.

Endophora Discussion The endophoric relationship is often spoken of as one expression “referring to” another.  Examples (English) A well-dressed man was speaking; he had a foreign accent. If you need one, there’s a towel in the top drawer.

Anaphora and Deixis He seems remarkably bright for a child of his age. George is only 4 but can read and write in both English and Bulgarian. He seems remarkably bright for a child of his age. I want you to be here now. Maggie came to England when she was four, and has lived here ever since

Anaphora resolution Anaphora resolution: the process of determining the antecedent of an anaphor Identity-of-reference nominal anaphora: preceding lexical noun phrases that are coreferential with the anaphor(s) are regarded as a legitimate antecedent Sophia Loren says she will always be grateful to Bono. The actress revealed that the U2 singer helped her calm down when she became scared by a thunderstorm while travelling on a plane.

Coreference resolution Idenification of all coreferential chains Sophia Loren says she will always be grateful to Bono. The actress revealed that the U2 singer helped her calm down when she became scared by a thunderstorm while travelling on a plane. Coreferential chains: {Sophia Loren, she, the actress, her, she}, {Bono, the U2 singer}, {a thunderstorm}, {a plane}