Notes on computational linguistics.pdf - UCLA Department of ...

Stabler - Lx 185/209 2003
which we can abbreviate unambiguously by the lexical sequence
ɛ::=T C -s::v=> +k T ɛ::=>V =D v have::=D +k V a::=Num D -k ɛ::=N Num car::N I::D -k
or, for convenience, even more briefly with something like:
C(-s(v(have(a(Num(car))),I))) or even have(a(car),I).
These structures cannot generally be translated into the first order predicate calculus, since they can have
non-first-order quantifiers like most, modal operators like tense, etc.
Another respect in which the syntactic structures differ from the ones considered by Jurafsky and Martin is
that their structures refer to “havers” and “had things”. That idea is similar to the proposal that we should
be able to recognize the subject of have as the “agent” and the object is the “theme.”
In transformational grammar, it is often proposed that these semantic, “thematic” roles of the arguments
of a predicate should be identifiable from the structure. A strong form of this idea was proposed by Baker
(1988) for example, in something like the following form:
Uniformity of Theta Assignment Hypothesis (UTAH): identical thematic relationships between items are
represented by identical structural relationships between those items in the positions where they are
selected (before movement).
So for example, we might propose
(H) the specifier of v is always the agent of the V that v selects.
(Actually, the proposal will need to be a little more complex that this, but let’s start with this simple idea).
A potential problem for this simple proposal comes with verbs that exhibit what is sometimes called the
“causative alternation”:
a. i. Titus break -s the vase
ii. The vase break -s
b. i. Titus open -s the window
ii. The window open -s
c. i. The wind clear -s the sky
ii. The sky clear -s
In the a examples, the subject is the agent and the object is the theme, as usual, but the b examples cause
a problem for H and UTAH, because there, it seems, the subject is the theme.
This problem for H and UTAH can be avoided if we assume that the single argument forms are not simple
intransitives like laugh, but are a different class of verb, where the verb selects just an object, not a subject.
One way to have this happen is to provide lexical entries that will generate trees like this:
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