SOME PROBLEMATIC CASES OF VP ELLIPSIS 
Daniel Hardt 
Department of Computer and Information Science 
University of Pennsylvania 
Philadelphia, PA 19104 
Internet: hardt~linc.cis.upenn.edu 
INTRODUCTION 
It has been widely assumed that VP ellipsis is gov- 
erned by an identity condition: the elided VP is in- 
terpreted as an identical copy of another expression 
in surrounding discourse. For example, Sag (76) 
imposes an identity condition on Logical Form rep- 
resentations of VP's. A basic feature of this ac- 
count is the requirement that a syntactic VP be 
available as the antecedent. This requirement is re- 
flected in most subsequent accounts as well. In this 
paper I examine three cases of VP ellipsis in which 
the antecedent cannot be identified with any VP. 
These cases, which are illustrated using naturally- 
occurring examples, present a fundamental problem 
for any of the standard approaches. I will argue 
that they receive a natural treatment in the system 
I have developed, in which VP ellipsis is treated by 
storing VP meanings in a discourse model. 
I will address the following three problems: 
• Combined Antecedents: The antecedent may be a 
combination of more than one previous property. 
• Passive Antecedents: the antecedent in a passive 
clause may not be associated with any VP, but, 
rather, the property associated with the active 
counterpart of that clause. 
• NP Antecedents: the antecedent may be a prop- 
erty associated with an NP. 
In what follows, I sketch my general approach 
to VP ellipsis, after which I show how each of the 
above phenomena can be treated in this approach. 
BACKGROUND 
VP ellipsis, I suggest, is to be explained along the 
lines of familiar accounts of pronominal anaphora 
(e.g., Kamp 80, Heim 81). A discourse model is 
posited, containing various semantic objects, includ- 
ing (among other things) entities and properties 
that have been evoked in preceding discourse. Typ- 
ically, entities are evoked by NP's, and properties 
by VP's. The interpretation of a pronoun involves a 
selection among the entities stored in the discourse 
model. Similarly, the interpretation of an elliptical 
VP involves a selection among the properties stored 
276 
in the discourse model. 1 I have described an imple- 
mentation along these lines in Hardt 91, based on 
some extensions to the Incremental Interpretation 
System (Pereira and Pollack 91). 
There are two rules governing VP ellipsis: one 
allowing the introduction of properties into the dis- 
course model, and another allowing the recovery of 
properties from the discourse model. 
These two rules are given below. In general, I 
assume the form of grammar in Pereira and Pollack 
91, in which all semantic rules take the input and 
output discourse models as arguments. That is, all 
semantic rules define relations on discourse models, 
or "file change potentials", in Heim's terms. 
The (simplified) rule for recovering a property 
from the discourse model is: 
AUX =~ P 
where P e DMi,,. 
That is, an auxiliary verb is replaced by some 
property P stored in the input discourse model. 
Secondly, properties are introduced into the dis- 
course model by the following rule: 
Upon encountering a property-denoting seman- 
tic object of the form: 
P(-, al) 
that is, a predicate with the first argument slot 
empty, we have: 
DMout = DMin U {P(-, at)} 
This indicates that the property is added to the 
output discourse model. Typically, the property- 
denoting expression is associated with a VP, al- 
though other types of expressions can also introduce 
properties into the discourse model. 
I have argued elsewhere (Hardt 91, 91a) that 
such a system has certain important advantages over 
alternative approaches, such as those of Sag (76) 
and Williams (77). 2 
1To be precise, it is not properties that are stored as 
VPE antecedents, but relations involving an input and 
output discourse context as well as a property. 
2The DRT-based account of Klein (87) essentially du- 
In what follows, I will briefly examine the phe- 
nomena listed above, which present fundamental 
problems for all accounts of VP ellipsis of which 
I am aware a. For each problem, I will suggest that 
the current approach provides a solution. 
COMBINED ANTECEDENTS 
There are cases of VP ellipsis in which the an- 
tecedent is combined from two or more separate 
VP's. This presents a problem for most accounts of 
VP ellipsis, since there is no syntactic object con- 
sisting of the combination of two separate VP's. If 
antecedents are stored in the discourse model, as I 
am suggesting, this is not surprising. For example, 
it is well known that combinations of entities can be- 
come the antecedent for a plural pronoun. Consider 
the following example: 
After the symmetry between left-handed 
particles and right-handed anti- particles was 
broken by the kaons in the 1960s, a new symme- 
try was introduced which everybody swears is 
unbreakable. This is between left-handed par- 
ticles moving forwards in time, and right- 
handed anti-particles moving backwards in 
time (none do, in any practical sense, but that 
does not worry theorists too much). 
From: The Economist, ~ August 1990, p.69. 
Bonnie Webber, p.c. 
The meaning of the elided VP ("none do") is, 
I take it, "none do move forwards or move back- 
. wards in time". So the antecedent must consists of a 
combination of properties associated with two VP's: 
"moving forwards in time" and "moving backwards 
in time". 
Such an example indicates the necessity for a 
rule allowing the set of properties in the discourse 
model to be expanded, as follows: 
{P...Q...} :~ {P...Q...\[P OP Q\]} 
That is, if the discourse model contains two 
properties P and Q, it may also contain the property 
resulting from a combination of P and Q by some 
operator (I assume that the operators include AND 
and OR). 
Another example is the following: 
So I say to the conspiracy fans: leave him 
alone. Leave us alone. But they won't. 
From: The Welcomat, 5 Feb 92, p.25 
Here the meaning of the elliptical VP is: "they 
won't leave him alone or leave us alone". 
plicates the Sag/Williams approach in DRT. Of partic- 
ulax relevance here is Klein's requirement that the an- 
tecedent be a DRT-representation of a syntactic VP. 
3The recent account of Dadrymple, Shieber and 
Pereira (91) does treat the "Passive Antecedent" prob- 
lem. However, no treatment of the "Combined An- 
tecedent" or "NP Antecedent" problems is given. 277 
This phenomenon has been noted in the liter- 
ature, in particular by Webber (?8), in which the 
following examples were given: 
I can walk, and I can chew gum. Gerry 
can too, but not at the same time. 
Wendy is eager to sail around the world 
and Bruce is eager to climb KiHmanjaro, but 
neither of them can because money is too tight. 
By the rule given above, this example could be 
given the interpretation "neither of them can sail 
around the world or climb Kilimanjaro". 
It is clear that the combining operation is highly 
constrained. In all the examples mentioned, either 
P and Q have the same subject, or the subject of 
the elliptical VP refers to the two subjects of P and 
Q. In future work, I will attempt to formulate con- 
straints on this operation. 
PASSIVE ANTECEDENTS 
The next problem is illustrated by the following 
example, cited by Dalrymple, Shieber and Pereira (91): 
A lot of this material can be presented in a 
fairly informal and accessible fashion, and often 
I do. 
From: Noam Chow_sky on the Generative En- 
terprise, Foris Publications, Dordrecht. 1982. 
The antecedent for the elliptical VP is "present 
a lot of this material in a fairly informal and acces- 
sible fashion". This is not associated with a VP, al- 
though the active counterpart of the sentence would 
contain such a VP. This is not surprising from a se- 
mantic point of view, since it is traditionally held 
that a 'passive transformation' preserves semantic 
equivalence. 
Another example of this is following: 
Business has to be developed and de- 
fended differently than we have in the past. 
From: NPR interview, 24 May 91 
The most straightforward treatment of such 
phenomena in the current framework is to assume 
that the syntactic derivation of a passive antecedent 
such as "this material can be presented" corre- 
sponds to a semantic object 
present(_, this material) 
More generally, for a syntactic expression 
SUBJ be VP+en 
the corresponding semantic object is 
VP'(-, SUB:V) 
That is, the denotation of the "surface subject" 
becomes the second argument of the VP-denotation. 
This semantic object, then, satisfies the condition 
on the rule for introducing properties given above. 
Thus, under such a treatment of the passive, these 
examples are accommodated in the present system 
without further stipulations. 
NP ANTECEDENTS 
In many casgs~ the antecedent property is intro- 
duced by a NP rather than a VP. This would be 
difficult to explain for a syntactic or logical form 
theory. From a semantic point of view, it is not sur- 
prising, since many NP's contain a common noun 
which is standardly analyzed semantically as denot- 
ing a property. Consider the following (naturally 
occurring) example: 
We should suggest to her that she officially 
appoint us as a committee and invite fac- 
ulty participation/input. They won't, of 
course,... 
From: email message. (Bonnie Webber, p.c.) 
In this example, the meaning of the elided VP 
is '%hey won't participate". The source is the NP 
"faculty participation". 
Another example is the following: 
\[Many Chicago-area cabdrivers\] say their 
business is foundering because the riders they 
depend on - business people, downtown work- 
ers and the elderly - are opting for the bus and 
the elevated train, or are on the unemployment 
line. Meanwhile, they sense a drop in visitors 
to the city. Those who do, they say, are not 
taking cabs. 
From: Chicago Tribune front page, ~/6/92. 
Gregory Ward, p.c. 
Here, the meaning of the elided VP is %hose 
who do visit", where the source is the NP "visitors". 
In the current framework, such examples could 
be treated as follows. Assume, following Chierchia 
(84), that there is a class of nouns that are semanti- 
cally correlated with properties. For any such noun, 
the associated property can be added to the dis- 
course model, just as is done for verbs. 
CONCLUSIONS 
The cases investigated constitute strong evidence 
that VP ellipsis must be explained at a seman- 
tic/discourse level. I have argued that the examples 
can be dealt with in the system I have developed. 
In future work, I will formulate constraints on the 
operations described here. 
ACKNOWLEDGEMENTS 
Thanks to Aravind Joshi, Shalom Lappin, Gregory 
Ward, and Bonnie Webber. This work was sup- 
ported by the following grants: ARO DAAL 03- 
89-C-0031, DARPA N00014-90-J-1863, NSF IRI 90- 
16592, and Ben Franklin 91S.3078C-1. 278 

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