Ling 566 Oct 13, 2016

Transcription

1 Ling 5 Oct 13, 201 Semantics

2 Overview Some notes on the linguist s stance Which aspects of semantics we ll tackle Our formalization; Semantics Principles Building semantics of phrases Modification, coordination Structural ambiguity Reading questions 2

3 The Linguist's Stance: Building a precise model Some of our statements are statements about how the model works: prep and AGR 3sing can t be combined because AGR is not a feature of the type prep. Some of our statements are statements about how (we think) English or language in general works. The determiners a and many only occur with count nouns, the determiner much only occurs with mass nouns, and the determiner the occurs with either. Some are statements about how we code a particular linguistic fact within the model. All count nouns are SPR < COUNT +>. 3

4 The Linguist's Stance: A Vista on the Set of Possible English Sentences... as a background against which linguistic elements (words, phrases) have a distribution... as an arena in which linguistic elements behave in certain ways 4

5 Semantics: Where's the Beef? So far, our grammar has no semantic representations. We have, however, been relying on semantic intuitions in our argumentation, and discussing semantic contrasts where they line up (or don't) with syntactic ones. Examples? structural ambiguity S/NP parallelism count/mass distinction complements vs. modifiers 5

6 Our Slice of a World of Meanings Aspects of meaning we won t account for Pragmatics Fine-grained lexical semantics: The meaning of life is life, or, in our case, INST life i

7 Our Slice of a World of Meanings MODE INDEX RESTR prop s SIT SAVER SAVED save s i, j NAME NAMED name Chris, i NAME NAMED name Pat j... the linguistic meaning of Chris saved Pat is a proposition that will be true just in case there is an actual situation that involves the saving of someone named Pat by someone named Chris. (p. 140)

8 Our Slice of a World of Meanings What we are accounting for is the compositionality of sentence meaning. How the pieces fit together Semantic arguments and indices How the meanings of the parts add up to the meaning of the whole. Appending RESTR lists up the tree 8

9 Semantics in Constraint-Based Grammar Constraints as (generalized) truth conditions proposition: what must be the case for a proposition to be true directive: what must happen for a directive to be fulfilled question: the kind of situation the asker is asking about reference: the kind of entity the speaker is referring to Syntax/semantics interface: Constraints on how syntactic arguments are related to semantic ones, and on how semantic information is compiled from different parts of the sentence. 9

10 Feature Geometry SYN SEM HEAD VAL MODE INDEX RESTR pos SPR COMPS list(expression) list(expression) { prop, ques, dir, ref, none} { i, j, k,... s 1, s 2,... } list(pred) 10

11 How the Pieces Fit Together Dana, word SYN HEAD noun AGR 3sing VAL SPR COMPS SEM INDEX i MODE ref RESTR name NAME Dana NAMED i 11

12 How the Pieces Fit Together slept, word SYN SEM HEAD verb SPR NPj VAL COMPS INDEX s 1 MODE prop sleep RESTR SIT s 1,... SLEEPER j 12

13 The Pieces Together S 1 NP SEM INDEX i VP SYN VAL SPR 1 SEM RESTR SIT s 1 SLEEPER i sleep,... Dana slept 13

14 A More Detailed View of the Same Tree SEM S INDEX MODE RESTR SEM INDEX RESTR 1 NP i name NAME Dana NAMED i VP SYN VAL SPR 1 SEM RESTR SIT s 1 SLEEPER i sleep,... 14

15 To Fill in Semantics for the S-node We need the Semantics Principles The Semantic Inheritance Principle: In any headed phrase, the mother's MODE and INDEX are identical to those of the head daughter. The Semantic Compositionality Principle: 15

16 Semantic Inheritance Illustrated SEM S INDEX s 1 MODE RESTR prop SEM INDEX RESTR 1 NP i name NAME Dana NAMED i VP SYN VAL SPR 1 SEM RESTR SIT s 1 SLEEPER i sleep,... 1

17 To Fill in Semantics for the S-node We need the Semantics Principles The Semantic Inheritance Principle: In any headed phrase, the mother's MODE and INDEX are identical to those of the head daughter. The Semantic Compositionality Principle: In any well-formed phrase structure, the mother's RESTR value is the sum of the RESTR values of the daughter. 1

18 Semantic Compositionality Illustrated SEM INDEX s 1 MODE RESTR prop NAME NAMED i S name Dana, SIT s 1 SLEEPER i sleep,... SEM INDEX RESTR 1 NP i name NAME Dana NAMED i VP SYN VAL SPR 1 SEM RESTR SIT s 1 SLEEPER i sleep,... 18

19 What Identifies Indices? S 1 NP i VPSPR 1 D NOM i SPR 1 RESTR VP SIT s 3 SLEEPER i sleep PP the cat slept on the mat 19

20 contribute predications slept, word SYN SEM Summary: Words... expose one index in those predications, for use by words or phrases relate syntactic arguments to semantic arguments HEAD verb SPR NP j VAL COMPS INDEX s 1 MODE prop sleep RESTR SIT s 1,... SLEEPER j

21 Summary: Grammar Rules... identify feature structures (including the INDEX value) across daughters Head Specifier Rule phrase SYN VAL SPR 1 HSYN VAL SPR 1 COMPS Head Complement Rule phrase SYN VAL COMPS word H SYN VAL COMPS 1,..., n 1... n Head Modifier Rule phrase H 1 SYN COMPS COMPS SYN VAL MOD 1 21

22 Summary: Grammar Rules... identify feature structures (including the INDEX value) across daughters license trees which are subject to the semantic principles - SIP passes up MODE and INDEX from head daughter SEM INDEX s 1 MODE RESTR prop NAME NAMED i S name Dana, SIT s 1 SLEEPER i sleep,... SEM INDEX RESTR 1 NP i name NAME Dana NAMED i VP SYN VAL SPR 1 SEM INDEX s 1 MODE RESTR prop SIT s 1 SLEEPER i sleep,... 22

23 Summary: Grammar Rules... identify feature structures (including the INDEX value) across daughters license trees which are subject to the semantic principles - SIP passes up MODE and INDEX from head daughter - SCP: gathers up predications (RESTR list) from all daughters SEM INDEX s 1 MODE RESTR prop NAME NAMED i S name Dana, SIT s 1 SLEEPER i sleep,... SEM INDEX RESTR 1 NP i name NAME Dana NAMED i VP SYN VAL SPR 1 SEM INDEX s 1 MODE RESTR prop SIT s 1 SLEEPER i sleep,... 23

24 Other Aspects of Semantics Tense, Quantification (only touched on here) Modification Coordination Structural Ambiguity 24

25 Evolution of a Phrase Structure Rule Ch. 2: NOM --> NOM PP VP --> VP PP Ch. 3: phrase VAL Ch. 4: phrase H Ch. 5: phrase H 1 COMPS itr H phrase VAL SPR VAL SYN SPR COMPS PP PP VAL COMPS COMPS SYN VAL MOD 1 COMPS Ch. 5 (abbreviated): phrase H 1 COMPS MOD 1 25

26 Evolution of Another Phrase Structure Rule Ch. 2: X --> X + CONJ X Ch. 3: word Ch. 4: Ch. 5: VAL 1 HEAD SYN VAL 0 SEM IND s 0 conj VAL 1 + SYN VAL 0 SYN VAL 0... SEM IND s 1 SEM IND s n 1 Ch. 5 (abbreviated): VAL 0 IND s 0 1 word HEAD SYN SEM conj VAL 1 HEAD conj IND s 0 RESTR ARGS s 1...s n HEAD conj VAL 0 VAL 0... IND s 0 IND s 1 IND s n 1 RESTR ARGS s 1...s n 2 SYN VAL 0 SEM IND s n VAL 0 IND s n

27 Combining Constraints and Coordination Coordination Rule VAL 0 IND s 0 HEAD conj VAL 0 VAL 0... IND s 0 IND s 1 IND s n 1 RESTR ARGS s 1...s n VAL 0 IND s n Lexical Entry for a Conjunction and, SYN SEM HEAD INDEX MODE RESTR conj s none SIT and s 2

28 Combining S IND s 0 Constraints and Coordination Lexical Entry for and SYN HEAD conj INDEX s and, MODE none SEM and RESTR SIT s S IND s 1 HEAD conj IND s 0 RESTR and SIT s 0 ARGS s 1, s 2 S IND s 2 Coordination Rule VAL 0 IND s 0 VAL 0... IND s 1 Pat sings HEAD conj VAL 0 IND s 0 IND s n 1 RESTR ARGS s 1...s n and VAL 0 IND s n Lee dances

29 S IND s 0 Structural Ambiguity, 1 S IND s 0 ADV MOD 1 Tree I S IND s 1 CONJ S IND s 2 frequently NP VP and NP VP Pat sings Lee dances IND s 0 MODE prop name sing and NAME Pat, SIT s 1, SIT s 0, NAMED k SINGER k ARGS s 1, s 2 RESTR name dance frequently NAME Lee, SIT s 2, ARG s 0 NAMED j DANCER j

30 S IND s 0 Structural Ambiguity, S IND s 1 CONJ S IND s 2 Tree II NP VP and 1 S IND s 2 ADV MOD 1 Pat sings NP VP frequently IND s 0 MODE prop NAME NAMED RESTR NAME NAMED Lee dances name sing and Pat, SIT s 1, SIT s 0, k SINGER k ARGS s 1, s 2 name dance frequently Lee, SIT s 2, ARG s 2 j DANCER j

31 Question About Structural Ambiguity Why isn t this a possible semantic representation for the string Pat sings and Lee dances frequently? IND s 0 MODE prop NAME NAMED RESTR NAME NAMED name sing and Pat, SIT s 1, SIT s 0, k SINGER k ARGS s 1, s 2 name dance frequently Lee, SIT s 2, ARG s 1 j DANCER j 31

32 IND s 0 MODE prop NAME NAMED RESTR NAME NAMED IND s 0 MODE prop NAME NAMED RESTR NAME NAMED Semantic Compositionality name sing and Pat, SIT s 1, SIT s 0, k SINGER k ARGS s 1, s 2 name dance frequently Lee, SIT s 2, ARG s 0 j DANCER j name sing and Pat, SIT s 1, SIT s 0, k SINGER k ARGS s 1, s 2 name dance frequently Lee, SIT s 2, ARG s 2 j DANCER j 32

33 Overview Some notes on the linguist s stance Which aspects of semantics we ll tackle Our formalization; Semantics Principles Building semantics of phrases Modification, coordination Structural ambiguity Next time: How the grammar works 33

34 Reading Questions Won't all those predicate-specific role names lead to too many features? Wouldn't theta-roles be better? Why are some more bland (e.g. ISNT)? Why do some nouns get NAME & NAMED and others just INST? 34

35 Reading Questions Are RESTR values the same as semantic frames? How do these RESTR values correspond to the predicate logic expressions we usually see in semantics classes? What are the RESTR values eventually used for? They're concatenated and passed up the tree, but I don't think this chapter gave an example of what we do with the final list in the top S node. Will they be necessary for syntactic parsing, or are we just storing them for applications that need semantic info? 35

36 Reading Questions What does the INDEX value do that isn't covered by RESTR (or by SIT in RESTR)? Does the SIP have directionality? In figure 52, for determiner "a" the value for INDEX is "i" and the value for BV is "i" - this seems redundant. Why have both specified? 3

37 3 * a, 2 4 word SYN 2 4 HEAD 2 4 det AGR 3sing COUNT VAL 2 4 COMPS hi SPR hi MOD hi SEM 2 4 MODE none INDEX i RESTR *" exist BV i #

38 Reading Questions Are we better equipped now to handle ambiguity (lexical or structural) than with previous chapters? We've started sharing semantic information between expressions in a tree, but it does yet have any affect on the syntax? Will it later? 38

39 Reading Questions How does the idea of propositions being true or false tie in with the syntactic structure? On pg 135, it indicates that your proposition has to meet all of its truth conditions. But if you say "Kim is running" and it is actually someone else running in the real world, does that really change anything about the meaning of the sentence? What if the proposition is a paradox? 39

40 Reading Questions On Pg. 144 states that the order of the elements in RESTR lists has no semantic significance. Why is it said so? Wouldn t the order matter as we go from LEFT to RIGHT daughter? 40

41 Reading Questions Some words and phrases (such as conjunctions and determiners) cannot take the MODE value "none" instead of the four primary MODE values {prop, ques, dir, ref}. If the types that can take {prop, ques, dir, ref} and the types that can take {none} are mutually exclusive then why do they inherit from the same sem-cat with all five values. 41

42 Reading Questions I would also seem that semantic features can occur inside syntactic categories, as in (35) on p. 14. May I assume that it's also true vice versa? And more broadly, are we supposed to memorize the fast-growing number of rules, features and principles? 42

43 * today, 2 SYN SEM 4 2 HEAD VAL 4 2 MODE 4RESTR adv 2 MOD 4SPR COMPS none *" * + hindex VP i s 1 h i h i ARG s 1 3 #+ today

44 Reading Questions Quantifiers? Scope? Copestake et al 2005 Minimal Recursion Semantics: An Introduction Where can I learn more about pragmatics? Levinson 2000 Presumptive meanings: The theory of generalized conversational implicature 44

45 Reading Questions 45