Communication Classical view (pre-1953): language consists of - PDF document

Communication “Classical” view (pre-1953): language consists of sentences that are true/false (cf. logic) “Modern” view (post-1953): Communication and Language language is a form of action Wittgenstein (1953) Philosophical Investigations Austin (1962) How to Do Things with Words Searle (1969) Speech Acts Chapter 22 Why? Chapter 22 1 Chapter 22 4 Outline Communication ♦ Communication “Classical” view (pre-1953): language consists of sentences that are true/false (cf. logic) ♦ Grammar “Modern” view (post-1953): ♦ Syntactic analysis language is a form of action ♦ Problems Wittgenstein (1953) Philosophical Investigations Austin (1962) How to Do Things with Words Searle (1969) Speech Acts Why? Chapter 22 2 Chapter 22 5 Communication Communication “Classical” view (pre-1953): “Classical” view (pre-1953): language consists of sentences that are true/false (cf. logic) language consists of sentences that are true/false (cf. logic) “Modern” view (post-1953): “Modern” view (post-1953): language is a form of action language is a form of action Wittgenstein (1953) Philosophical Investigations Wittgenstein (1953) Philosophical Investigations Austin (1962) How to Do Things with Words Austin (1962) How to Do Things with Words Searle (1969) Speech Acts Searle (1969) Speech Acts Why? Why? To change the actions of other agents Chapter 22 3 Chapter 22 6

Speech acts Grammar Vervet monkeys, antelopes etc. use isolated symbols for sentences SITUATION ⇒ restricted set of communicable propositions, no generative capacity Speaker Utterance Hearer (Chomsky (1957): Syntactic Structures ) Grammar specifies the compositional structure of complex messages e.g., speech (linear), text (linear), music (two-dimensional) Speech acts achieve the speaker’s goals: A formal language is a set of strings of terminal symbols Inform “There’s a pit in front of you” “Can you see the gold?” Query Each string in the language can be analyzed/generated by the grammar Command “Pick it up” “I’ll share the gold with you” Promise The grammar is a set of rewrite rules, e.g., Acknowledge “OK” S → NP VP Speech act planning requires knowledge of Article → the | a | an | . . . – Situation Here S is the sentence symbol, NP and VP are nonterminals – Semantic and syntactic conventions – Hearer’s goals, knowledge base, and rationality Chapter 22 7 Chapter 22 10 Stages in communication (informing) Grammar types Regular: nonterminal → terminal [ nonterminal ] S wants to inform H that P Intention Generation S selects words W to express P in context C S → a S Synthesis S utters words W S → Λ H perceives W ′ in context C ′ Context-free: nonterminal → anything Perception Analysis H infers possible meanings P 1 , . . . P n S → a S b Disambiguation H infers intended meaning P i Incorporation H incorporates P i into KB Context-sensitive: more nonterminals on right-hand side How could this go wrong? ASB → AA a BB Recursively enumerable: no constraints Related to Post systems and Kleene systems of rewrite rules Natural languages probably context-free, parsable in real time! Chapter 22 8 Chapter 22 11 Stages in communication (informing) Wumpus lexicon Noun → stench | breeze | glitter | nothing S wants to inform H that P Intention Generation S selects words W to express P in context C | wumpus | pit | pits | gold | east | . . . Synthesis S utters words W Verb → is | see | smell | shoot | feel | stinks | go | grab | carry | kill | turn | . . . H perceives W ′ in context C ′ Perception Adjective → right | left | east | south | back | smelly | . . . Analysis H infers possible meanings P 1 , . . . P n Adverb → here | there | nearby | ahead Disambiguation H infers intended meaning P i | right | left | east | south | back | . . . Incorporation H incorporates P i into KB Pronoun → me | you | I | it | . . . How could this go wrong? Name → John | Mary | Boston | UCB | P AJC | . . . – Insincerity (S doesn’t believe P ) Article → the | a | an | . . . – Speech wreck ignition failure Preposition → to | in | on | near | . . . – Ambiguous utterance Conjunction → and | or | but | . . . – Differing understanding of current context ( C � = C ′ ) Digit → 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 Divided into closed and open classes Chapter 22 9 Chapter 22 12

Wumpus lexicon Parse trees Exhibit the grammatical structure of a sentence Noun → stench | breeze | glitter | nothing | wumpus | pit | pits | gold | east | . . . Verb → is | see | smell | shoot | feel | stinks | go | grab | carry | kill | turn | . . . Adjective → right | left | east | south | back | smelly | . . . Adverb → here | there | nearby | ahead | right | left | east | south | back | . . . Pronoun → me | you | I | it | S/HE | Y ′ ALL . . . Name → John | Mary | Boston | UCB | P AJC | . . . Article → the | a | an | . . . Preposition → to | in | on | near | . . . Conjunction → and | or | but | . . . I shoot the wumpus Digit → 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 Divided into closed and open classes Chapter 22 13 Chapter 22 16 Wumpus grammar Parse trees S → NP VP I + feel a breeze Exhibit the grammatical structure of a sentence | I feel a breeze + and + I smell a wumpus S Conjunction S NP → Pronoun I | Noun pits | Article Noun the + wumpus | 3 4 Digit Digit | NP PP the wumpus + to the east | NP RelClause the wumpus + that is smelly VP → Verb stinks | feel + a breeze VP NP Pronoun Verb Article Noun | VP Adjective is + smelly | VP PP turn + to the east | go + ahead I shoot the wumpus VP Adverb PP → Preposition NP to + the east RelClause → that VP that + is smelly Chapter 22 14 Chapter 22 17 Grammaticality judgements Parse trees Formal language L 1 may differ from natural language L 2 Exhibit the grammatical structure of a sentence L 1 L 2 false false positives negatives NP VP NP Adjusting L 1 to agree with L 2 is a learning problem! * the gold grab the wumpus Pronoun Verb Article Noun * I smell the wumpus the gold I give the wumpus the gold I shoot the wumpus * I donate the wumpus the gold Intersubjective agreement somewhat reliable, independent of semantics! Real grammars 10–500 pages, insufficient even for “proper” English Chapter 22 15 Chapter 22 18

Parse trees Syntax in NLP Exhibit the grammatical structure of a sentence Most view syntactic structure as an essential step towards meaning; “Mary hit John” � = “John hit Mary” “And since I was not informed—as a matter of fact, since I did not know that there were excess funds until we, ourselves, in that checkup after the VP whole thing blew up, and that was, if you’ll remember, that was the incident in which the attorney general came to me and told me that he had seen a memo that indicated that there were no more funds.” NP VP NP “Wouldn’t the sentence ’I want to put a hyphen between the words Fish and And and And and Chips in my Fish-And-Chips sign’ have been clearer Pronoun Verb Article Noun if quotation marks had been placed before Fish, and between Fish and and, and and and And, and And and and, and and and And, and And and and, and and and Chips, as well as after Chips?” I shoot the wumpus Chapter 22 19 Chapter 22 22 Parse trees Context-free parsing Exhibit the grammatical structure of a sentence Bottom-up parsing works by replacing any substring that matches RHS of a rule with the rule’s LHS S Efficient algorithms (e.g., chart parsing, Section 22.3) O ( n 3 ) for context-free, run at several thousand words/sec for real grammars VP Context-free parsing ≡ Boolean matrix multiplication (Lee, 2002) ⇒ unlikely to find faster practical algorithms NP VP NP Pronoun Verb Article Noun I shoot the wumpus Chapter 22 20 Chapter 22 23 Syntax in NLP Logical grammars Most view syntactic structure as an essential step towards meaning; BNF notation for grammars too restrictive: “Mary hit John” � = “John hit Mary” – difficult to add “side conditions” (number agreement, etc.) – difficult to connect syntax to semantics “And since I was not informed—as a matter of fact, since I did not know that there were excess funds until we, ourselves, in that checkup after the Idea: express grammar rules as logic whole thing blew up, and that was, if you’ll remember, that was the incident X → YZ becomes Y ( s 1 ) ∧ Z ( s 2 ) ⇒ X ( Append ( s 1 , s 2 )) in which the attorney general came to me and told me that he had seen a X → word becomes X ([ “ word ” ]) memo that indicated that there were no more funds.” X → Y | Z becomes Y ( s ) ⇒ X ( s ) Z ( s ) ⇒ X ( s ) Here, X ( s ) means that string s can be interpreted as an X Chapter 22 21 Chapter 22 24