Michael Elhadad - NLP Fall 2021
Advanced Syntactic Issues and their Semantic Interpretation
We review in this lecture a set of "interesting" syntactic constructs in English
which present challenges to simple compositional CFG formulation:
Quantification / Scope
Consider the sentence:
Every man loves a woman
This has 2 possible semantic interpretations:
(i) For all x, man(x) ==> exits(y), woman(y) and love(x, y)
(ii) Exist y, woman(y) and for all x, man(x) ==> love(x, y)
The difference between these 2 interpretations comes from the relative
scoping of the quantifiers (introduced by the determiner every and
a).
A simple compositional interpretation approach fails to capture this
systematic ambiguity in quantifier scope. Cooper proposed a mechanism
known as Cooper Quantifier Storage to allow a compositional treatment
of quantifier scope ambiguity. (See Cooper, R., Quantification and
Syntactic Theory, 1983, D. Reidel, Dordrecht, Netherlands.)
An alternative compositional formulation called Hole Semantics
is presented in the book Representation and Inference for Natural
Language, Patrick Blackburn and Johan Bos, 2005.
Long Distance Dependency
Consider the examples:
- The man who _ likes Kim
- The man who Kim likes _
The sign _ indicates a gap in the embedded syntactic constituent (the
relative clause) which is filled by another NP from the containing
constituent (the head of the NP). The meaning of gap is that if we
were to extract the embedded clause, and try to express it as an
independent clause, it would be missing a constituent. This constituent
should be "filled" by a constituent of the matrix clause (the clause within
which the embedded clause appears).
Such structures can be recursively embedded - but there exist syntactic
constraints on the location of gaps:
- Which hypothesis did Kim deny that [Sandy had proved _
logically independent]?
- * Which hypothesis did Kim leave for NY [before Sandy had proved _
logically independent]?
Accessibility
Not all scoping combinations are possible for a given syntactic construct.
Consider the example:
(1) * A woman who saw every man disliked him.
(1) is not syntactically correct, while the following examples do
have a possible interpretation:
(2) Every man saw a friend of his.
(3) Every admirer of a picture of himself is vain.
(4) Every man who owns a donkey beats him.
The accessibility of certain NPs as arguments in various syntactic
locations is determined by properties of the NP (whether it is
a pronoun, reflexive, proper name, definite or indefinite reference)
and of the syntactic context. Similar constraints also explain
different scoping possibilities.
Binding and Control
- Mary thinks that John likes her.: her can refer either to Mary (default reading) or to a different female referent.
- Mary likes herself. - herself can only refer to Mary.
- Mary likes her. - her cannot refer to Mary.
- John bought a picture of himself.
- John thought that it would be illegal to undress himself.
- They met each other. (this is a reciprocal reference).
- John talked to Paul about himself. - himself can refer both to Paul and John.
- John talked about himself to Paul. - himself can only refer only to John.
Such observations are explained by the linguistic theory of binding,
which uses the definition of c-command to distinguish between accessible and inaccessible referents for anaphors.
;; binding
;; / \
;; referential expletive
;; / \ / \
;; npro pro it there
;; / \
;; ppro anaphor
;; / \
;; reflexive reciprocal
;;
Last modified Jan 10st, 2021