COMMON TOPICS AND COHERENT SITUATIONS: 
INTERPRETING ELLIPSIS IN THE CONTEXT OF 
DISCOURSE INFERENCE 
Andrew Kehler 
Harvard University 
Aiken Computation Laboratory 
33 Oxford Street 
Cambridge, MA 02138 
kehler@das.harvard.edu 
Abstract 
It is claimed that a variety of facts concerning ellip- 
sis, event reference, and interclausal coherence can be 
explained by two features of the linguistic form in ques- 
tion: (1) whether the form leaves behind an empty 
constituent in the syntax, and (2) whether the form 
is anaphoric in the semantics. It is proposed that these 
features interact with one of two types of discourse in- 
ference, namely Common Topic inference and Coherent 
Situation inference. The differing ways in which these 
types of inference utilize syntactic and semantic repre- 
sentations predicts phenomena for which it is otherwise 
difficult to account. 
Introduction 
Ellipsis is pervasive in natural language, and hence has 
received much attention within both computational and 
theoretical linguistics. However, the conditions under 
which a representation of an utterance may serve as 
a suitable basis for interpreting subsequent elliptical 
forms remain poorly understood; specifically, past at- 
tempts to characterize these processes within a single 
traditional module of language processing (e.g., consid- 
ering either syntax, semantics, or discourse in isolation) 
have failed to account for all of the data. In this paper, 
we claim that a variety of facts concerning ellipsis res- 
olution, event reference, and interclausal coherence can 
be explained by the interaction between the syntactic 
and semantic properties of the form in question and the 
type of discourse inference operative in establishing the 
coherence of the antecedent and elided clauses. 
In the next section, we introduce the facts concerning 
gapping, VP-ellipsis, and non-elliptical event reference 
that we seek to explain. In Section 3, we categorize 
elliptical and event referential forms according to two 
features: (1) whether the expression leaves behind an 
empty constituent in the syntax, and (2) whether the 
expression is anaphoric in the semantics. In Section 4 
we describe two types of discourse inference, namely 
Common Topic inference and Coherent Situation in- 
ference, and make a specific proposal concerning the 
interface between these and the syntactic and seman- 
tic representations they utilize. In Section 5, we show 
how this proposal accounts for the data presented in 
Section 2. We contrast the account with relevant past 
work in Section 6, and conclude in Section 7. 
Ellipsis and Interclausal Coherence 
It has been noted in previous work that the felicity of 
certain forms of ellipsis is dependent on the type of co- 
herence relationship extant between the antecedent and 
elided clauses (Levin and Prince, 1982; Kehler, 1993b). 
In this section we review the relevant facts for two such 
forms of ellipsis, namely gapping and VP-ellipsis, and 
also compare these with facts concerning non-elliptical 
event reference. 
Gapping is characterized by an antecedent sentence 
(henceforth called the source sentence) and the elision of 
all but two constituents (and in limited circumstances, 
more than two constituents) in one or more subsequent 
target sentences, as exemplified in sentence (1): 
(1) Bill became upset, and Hillary angry. 
We are concerned here with a particular fact about gap- 
ping noticed by Levin and Prince (1982), namely that 
gapping is acceptable only with the purely conjunc- 
tive symmetric meaning of and conjoining the clauses, 
and not with its causal asymmetric meaning (para- 
phraseable by "and as a result"). That is, while either 
of sentences (1) or (2) can have the purely conjunctive 
reading, only sentence (2) can be understood to mean 
that Hillary's becoming angry was caused by or came 
as a result of Bill's becoming upset. 
(2) Bill became upset, and Hillary became angry. 
This can be seen by embedding each of these examples 
in a context that reinforces one of the meanings. For 
instance, gapping is felicitous in passage (3), where con- 
text supports the symmetric reading, but is infelicitous 
in passage (4) under the intended causal meaning of 
and. 1 
1This behavior is not limited to the conjunction and; a 
similar distinction holds between symmetric and asymmet- 
ric uses of or and but. See Kehler (1994) for further discus- 
sion. 
50 
(3) The Clintons want to get the national debate fo- 
cussed on health care, and are getting annoyed 
because the media is preoccupied with Whitewa- 
ter. When a reporter recently asked a Whitewater 
question at a health care rally, Bill became upset, 
and Hillary became/0 angry. 
(4) Hillary has been getting annoyed at Bill for his in- 
ability to deflect controversy and do damage con- 
trol. She has repeatedly told him that the way 
to deal with Whitewater is to play it down and 
not to overreact. When a reporter recently asked 
a Whitewater question at a health care rally, Bill 
became upset, and (as a result) Hillary became/# 
angry. 
The common stipulation within the literature stating 
that gapping applies to coordinate structures and not 
to subordinate ones does not account for why any co- 
ordinated cases are unacceptable. 
VP-ellipsis is characterized by an initial source sen- 
tence, and a subsequent target sentence with a bare 
auxiliary indicating the elision of a verb phrase: 
(5) Bill became upset, and Hillary did too. 
The distribution of VP-ellipsis has also been shown 
to be sensitive to the coherence relationship extant be- 
tween the source and target clauses, but in a differ- 
ent respect. In a previous paper (Kehler, 1993b), five 
contexts for VP-ellipsis were examined to determine 
whether the representations retrieved are syntactic or 
semantic in nature. Evidence was given that VP-ellipsis 
copies syntactic representations in what was termed 
parallelconstructions (predicting the unacceptability of 
the voice mismatch in example (6) and nominalized 
source in example (8)), but copies semantic represen- 
tations in non-parallel constructions (predicting the ac- 
ceptability of the voice mismatch in example (7) and 
the nominalized source in example (9)): 2 
(6) # The decision was reversed by the FBI, and the 
ICC did too. \[ reverse the decision \] 
(7) In March, four fireworks manufacturers asked 
that the decision be reversed, and on Monday the 
ICC did. \[ reverse the decision \] 
(8) # This letter provoked a response from Bush, and 
Clinton did too. \[ respond \] 
(9) This letter was meant to provoke a response from 
Clinton, and so he did. \[ respond \] 
These examples are analogous with the gapping cases in 
that constraints against mismatches of syntactic form 
hold for the symmetric (i.e., parallel) use of and in 
examples (6) and (8), but not the asymmetric (i.e., 
non-parallel) meaning in examples (7) and (9). In 
2These examples have been taken or adapted from Kehler 
(1993b). The phrases shown in brackets indicate the elided 
material under the intended interpretation. 
fact, it appears that gapping is felicitous in those con- 
structions where VP-ellipsis requires a syntactic an- 
tecedent, whereas gapping is infelicitous in cases where 
VP-ellipsis requires only a suitable semantic antecedent. 
Past approaches to VP-ellipsis that operate within a 
single module of language processing fail to make the 
distinctions necessary to account for these differences. 
Sag and Hankamer (1984) note that while elliptical 
sentences such as (6) are unacceptable because of a 
voice mismatch, similar examples with non-elided event 
referential forms such as do it are much more accept- 
able: 
(10) The decision was reversed by the FBI, and the 
ICC did it too. \[ reverse the decision \] 
An adequate theory of ellipsis and event reference must 
account for this distinction. 
In sum, the felicity of both gapping and VP-ellipsis 
appears to be dependent on the type of coherence re- 
lation extant between the source and target clauses. 
Pronominal event reference, on the other hand, appears 
not to display this dependence. We seek to account for 
these facts in the sections that follow. 
Syntax and Semantics of Ellipsis and 
Event Reference 
In this section we characterize the forms being ad- 
dressed in terms of two features: (1) whether the form 
leaves behind an empty constituent in the syntax, and 
(2) whether the form is anaphoric in the semantics. In 
subsequent sections, we show how the distinct mecha- 
nisms for recovering these types of missing information 
interact with two types of discourse inference to predict 
the phenomena noted in the previous section. 
We illustrate the relevant syntactic and semantic 
properties of these forms using the version of Catego- 
rial Semantics described in Pereira (1990). In the Mon- 
tagovian tradition, semantic representations are com- 
positionaUy generated in correspondence with the con- 
stituent modification relationships manifest in the syn- 
tax; predicates are curried. Traces are associated with 
assumptions which are subsequently discharged by a 
suitable construction. Figure 1 shows the representa- 
tions for the sentence Bill became upset; this will serve 
as the initial source clause representation for the exam- 
ples that follow. 3 
For our analysis of gapping, we follow Sag (1976) in 
hypothesizing that a post-surface-structure level of syn- 
tactic representation is used as the basis for interpreta- 
tion. In source clauses of gapping constructions, con- 
stituents in the source that are parallel to the overt con- 
stituents in the target are abstracted out of the clause 
representation. 4 For simplicity, we will assume that 
3We will ignore the tense of the predicates for ease of 
exposition. 
4It has been noted that in gapping constructions, con- 
trastive accent is generally placed on parallel elements in 
51 
S: become '(upset ')(Bill') 
NP: Bill' VP: beeome'(upset') 
Bill: Bill' V: become' AP: upset' 
I I bec~ame: becx~me' upset: upset' 
Figure 1: Syntactic and Semantic Representations for 
Bill became upset. 
this abstraction is achieved by fronting the constituents 
in the post-surface-structure, although nothing much 
hinges on this; our analysis is compatible with several 
possible mechanisms. The syntactic and semantic rep- 
resentations for the source clause of example (1) after 
fronting are shown in Figure 2; the fronting leaves trace 
assumptions behind that are discharged when combined 
with their antecedents. 
S: bccomc'(upsct'XBill') \[tracc-abs\] 
hiP: Bill' S: beeome'(upset'X t o \[trae~abs\] 
Bill: Bill' ~: upset' S: become'(tuX tb) 
upset: upset' NP:t b \[~'ace-licl VP: become'(tu) 
t6 V: become' AP:t u \[Iraee-lic\] 
I I 
bee~me: become' 6 
Figure 2: Syntactic and Semantic Representations for 
Bill became upset after fronting. 
Target clauses in gapping constructions are therefore 
represented with the overt constituents fronted out of 
an elided sentence node; for instance the representation 
of the target clause in example (1) is shown in Figure 3 
both the target and the source clauses, and that abstracting 
these elements results in an "open proposition" that both 
clauses share (Sag, 1976; Prince, 1986; Steedman, 1990). 
This proposition needs to be presupposed (or accommo- 
dated) for the gapping to be felicitous, for instance, it would 
be infelicitous to open a conversation with sentence such as 
(1), whereas it is perfectly felicitous in response to the ques- 
tion How did the Clintons react?. Gapping resolution can 
be characterized as the restoration of this open proposition 
in the gapped clause. 
(the empty node is indicated by ¢). The empty con- 
s: 
NP: Hillary' S: 
HiUary: Hinary' AP: angry' S: 
I I 
angry: angry' ~5 
Figure 3: Syntactic and Semantic Representations for 
Hillary angry. 
stituent is reconstructed by copying the embedded sen- 
tence from the source to the target clause, along with 
parallel trace assumptions which are to be bound within 
the target. The semantics for this embedded sentence 
is the open proposition that the two clauses share. This 
semantics, we claim, can only be recovered by copying 
the syntax, as gapping does not result in an indepen- 
dently anaphoric expression in the semantics. ~ In fact, 
as can be seen from Figure 3, before copying takes place 
there is no sentence-level semantics for gapped clauses 
at all. 
Like gapping, VP-ellipsis results in an empty con- 
stituent in the syntax, in this case, a verb phrase. How- 
ever, unlike gapping, VP-ellipsis also results in an inde- 
pendently anaphoric form in the semantics. 6 Figure 4 
shows the representations for the clause Hillary did (the 
anaphoric expression is indicated by P). 
J 
NP: Hillary' 
I 
ttillary: Hillary' 
S: P(Hillary') 
VP:P 
AUX: '~Q.Q VP: P \[l~-on-lic\] I 
did: AQ.Q 
Figure 4: Syntactic and Semantic Representations for 
Hillary did. 
Given the representation in Figure 1 as the source, 
the semantics for the missing VP may be recovered in 
5This claim is supported by well-established facts sug- 
gesting that gapping does not pattern with standard forms 
of anaphora. For instance, unlike VP-ellipsis and overt pro- 
nouns, gapping cannot be cataphoric, and can only obtain 
its antecedent from the immediately preceding clause. 
6Unlike gapping, VP-ellipsis patterns with other types of 
anaphora, for instance it can be cataphoric and can locate 
antecedents from clauses other than the most immediate 
one. 
52 
one of two ways. The syntactic VP could be copied 
down with its corresponding semantics, from which the 
semantics for the complete sentence can be derived. In 
this case, the anaphoric expression is constrained to 
have the same semantics as the copied constituent. Al- 
ternatively, the anaphoric expression could be resolved 
purely semantically, resulting in the discharge of the 
anaphoric assumption P. The higher-order unification 
method developed by Dalrymple et al. (1991) could be 
used for this purpose; in this case the sentence-level 
semantics is recovered without copying any syntactic 
representations. 
Event referential forms such as do it, do tha~, and do 
so constitute full verb phrases in the syntax. It has been 
often noted (Halliday and Hasan, 1976, inter alia) that 
it is the main verb do that is operative in these forms 
of anaphora, in contrast to the auxiliary do operative 
in VP-ellipsis/ It is the pronoun in event referential 
forms that is anaphoric; the fact that the pronouns refer 
to events results from the type constraints imposed by 
the main verb do. Therefore, such forms are anaphoric 
in the semantics, but do not leave behind an empty 
constituent in the syntax. 
To summarize this section, we have characterized the 
forms being addressed according to two features, a sum- 
mary of which appears in Table 1. Whereas anaphoric 
Form Empty Node Anaphoric \[\[ 
in Syntax in Semantics II 
Gapping ~/ 
VP-Ellipsis ~/ V / 
Event Reference ~/ 
Table l: Common Topic Relations 
forms in the semantics for these forms are indepen- 
dently resolved, empty syntactic constituents in and of 
themselves are not anaphoric, and thus may only be 
restored when some independently-motivated process 
necessitates it. In the section that follows we outline 
two types of discourse inference, one of which requires 
such copying of empty constituents. 
Discourse Inference 
To be coherent, utterances within a discourse segment 
require more than is embodied in their individual syn- 
tactic and semantic representations alone; additional 
rFor instance, other auxiliaries can appear in elided 
forms but cannot be followed by it, tt, at, or so as in ex- 
ample (11), and a pronominal object to the main verb do 
cannot refer to a state as VP-ellipsis can as in example (12). 
(11) George was going to the golf course and Bill was  /(# 
it)/(# that)/(# so) too. 
(12) Bill dislikes George and Hillary does fl/(# it)/(# 
that)/(# so) too. 
inter-utterance constraints must be met. Here we de- 
scribe two types of inference used to enforce the con- 
straints that are imposed by coherence relations. In 
each case, arguments to coherence relations take the 
form of semantic representations retrieved by way of 
their corresponding node(s) in the syntax; the oper- 
ations performed on these representations are dictated 
by the nature of the constraints imposed. The two types 
of inference are distinguished by the level in the syntax 
from which these arguments are retrieved, s 
Common Topic Inference 
Understanding segments of utterances standing in a 
Common Topic relation requires the determination 
of points of commonality (parallelism) and departure 
(contrast) between sets of corresponding entities and 
properties within the utterances. This process is reliant 
on performing comparison and generalization opera- 
tions on the corresponding representations (Scha and 
Polanyi, 1988; Hobbs, 1990; Priist, 1992; Asher, 1993). 
Table 2 sketches definitions for some Common Topic 
relations, some taken from and others adapted from 
Hobbs (1990). In each case, the hearer is to understand 
the relation by inferring po(al,..., a,) from sentence So 
and inferring p1(bl, ..., bn) from sentence $1 under the 
listed constraints. 9 In order to meet these constraints, 
the identification of p0 and Pl may require arbitrary lev- 
els of generalization from the relations explicitly stated 
in the utterances. 
Examples of these relations are given in sentences 
(13a-d). 
(13) a. John organized rallies for Clinton, and Fred 
distributed pamphlets for him. (Parallel) 
b. John supported Clinton, but Mary supported 
Bush. (Contrast) 
c. Young aspiring politicians usually support 
their party's presidential candidate. For in- 
stance, John campaigned hard for Clinton in 
1992. (Exemplification) 
d. A young aspiring politician was arrested in 
Texas today. John Smith, 34, was nabbed in 
a Houston law firm while attempting to em- 
bezzle funds for his campaign. (Elaboration) 
Passage (13a), for instance, is coherent under the un- 
derstanding that John and Fred have a common prop- 
SHobbs (1990), following Hume (1748), suggests a clas- 
sification of coherence relations into three broad cate- 
gories, namely Resemblance, Cause or Effect, and Contiguity 
(Hume's terminology). Here, Resemblance relations appear 
to pattern well with those employing our Common Topic 
inference, and likewise Cause or effect and Contiguity with 
our Coherent Situation inference. 
9Following Hobbs, by al and bi being similar we mean 
that for some salient property qi, qi(ai) and qi(b,) holds. 
Likewise by dissimilar we mean that for some qi, q,(al) and 
"~qi (bi ) holds. 
53 
Constraints Conjunctions \[I Relation 
Parallel 
Contrast 
Exemplification 
Elaboration 
Po = Pl, ai and bi are similar 
(1) Po = -~Pl, ai and bi are similar 
(2) P0 = Pl, ai and bi are dissimilar for some i 
Po =Pl ;bl Eaior biCai 
PO = pl , ai ---- bi 
and 
but 
for example ' 
in other words 
Table 2: Common Topic Relations 
erty, namely having done something to support Clin- 
ton. Passage (13c) is likewise coherent by virtue of the 
inferences resulting from identifying parallel elements 
and properties, including that John is a young aspiring 
politician and that he's a Democrat (since Clinton is 
identified with his party's candidate). The character- 
istic that Common Topic relations share is that they 
require the identification of parallel entities (i.e., the al 
and bi) and relations (P0 and Px) as arguments to the 
constraints. We posit that the syntactic representation 
is used both to guide the identification of parallel ele- 
ments and to retrieve their semantic representations. 
Coherent Situation Inference 
Understanding utterances standing in a Coherent Sit- 
uation relation requires that hearers convince them- 
selves that the utterances describe a coherent situation 
given their knowledge of the world. This process re- 
quires that a path of inference be established between 
the situations (i.e., events or states) described in the 
participating utterances as a whole, without regard to 
any constraints on parMlelism between sub-sententiM 
constituents. Four such relations are summarized in 
Table 3. l° In all four cases, the hearer is to infer A 
from sentence $1 and B from sentence $2 under the 
constraint that the presuppositions listed be abduced 
(ttobbs et al., 1993): 11 
Relation Presuppose Conjunctions 
Result 
Explanation 
Violated Expectation 
Denial of Preventer 
A-. B 
B--,A 
A ---* -, B 
B --* -~ A 
and (as a result) 
therefore 
because 
but 
even though 
despite 
Table 3: Coherent Situation Relations 
Examples of these relations are given in sentences 
(14a-d). 
(14) a. Bill is a politician, and therefore he's dishon- 
est. (Result) 
1°These relations are what Hume might have termed 
Cause or Effect. 
11We are using implication in a very loose sense here, as 
if to mean "could plausibly follow from". 
b. Bill is dishonest because he's a politician. 
(Explanation) 
c. Bill is a politician, but he's honest. 
(Violated Expectation) 
d. Bill is honest, even though he's a politician. 
(Denial of Preventer) 
Beyond what is asserted by the two clauses individually, 
understanding each of these sentences requires the pre- 
supposition that being a politician implies being dishon- 
est. Inferring this is only reliant on the sentential-level 
semantics for the clauses as a whole; there are no p, ai, 
or bi to be independently identified. The same is true 
for what Hume called Contiguity relations (perhaps in- 
eluding Hobbs' Occasion and Figure-ground relations); 
for the purpose of this paper we will consider these as 
weaker cases of Cause or Effect. 
To reiterate the crucial observation, Common Topic 
inference utilizes the syntactic structure in identify- 
ing the semantics for the sub-sentential constituents to 
serve as arguments to the coherence constraints. In 
contrast, Coherent Situation inference utilizes only the 
sentential-level semantic forms as is required for ab- 
ducing a coherent situation. The question then arises 
as to what happens when constituents in the syntax 
for an utterance are empty. Given that the discourse 
inference mechanisms retrieve semantic forms through 
nodes in the syntax, this syntax will have to be recov- 
ered when a node being accessed is missing. Therefore, 
we posit that missing constituents are recovered as a 
by-product of Common Topic inference, to allow the 
parallel properties and entities serving as arguments to 
the coherence relation to be accessed from within the re- 
constructed structure. On the other hand, such copying 
is not triggered in Coherent Situation inference, since 
the arguments are retrieved only from the top-level sen- 
tence node, which is always present. In the next section, 
we show how this difference accounts for the data given 
in Section 2. 
Applying the Analysis 
In previous sections, we have classified several ellip- 
tical and event referential forms as to whether they 
leave behind an empty constituent in the syntax and 
whether they are anaphoric in the semantics. Empty. 
constituents in the syntax are not in themselves refer- 
ential, but are recovered during Common Topic infer- 
54 
ence. Anaphoric expressions in the semantics are inde- 
pendently referential and are resolved through purely 
semantic means regardless of the type of discourse in- 
ference. In this section we show how the phenomena 
presented in Section 2 follow from these properties. 
Local Ellipsis 
Recall from Section 2 that gapping constructions such 
as (15) are only felicitous with the symmetric (i.e., 
Common Topic) meaning of and: 
(15) Bill became upset, and Hillary angry. 
This fact is predicted by our account in the following 
way. In the case of Common Topic constructions, the 
missing sentence in the target will be copied from the 
source, the sentential semantics may be derived, and the 
arguments to the coherence relations can be identified 
and reasoning carried out, predicting felicity. In the 
case of Coherent Situation relations, no such recovery 
of the syntax takes place. Since a gapped clause in and 
of itself has no sentence-level semantics, the gapping 
fails to be felicitous in these cases. 
This account also explains similar differences in fe- 
licity for other coordinating conjunctions as discussed 
in Kehler (1994), as well as why gapping is infelicitous 
in constructions with subordinating conjunctions indi- 
cating Coherent Situation relations, as exemplified in 
(16). 
(16) # Bill became upset, 
{ because } 
even though Hillary angry. 
despite the fact that 
The stripping construction is similar to gapping ex- 
cept that there is only one bare constituent in the tar- 
get (also generally receiving contrastive accent); unlike 
VP-ellipsis there is no stranded auxiliary. We therefore 
might predict that stripping is also acceptable in Com- 
mon Topic constructions but not in Coherent Situation 
constructions, which appears to be the case: 12 
(17) Bill became upset, 
but not 
# and (as a result) # because Hillary. 
# even though 
# despite the fact that 
In summary, gapping and related constructions are 
infelicitous in those cases where Coherent Situation in- 
ference is employed, as there is no mechanism for re- 
covering the sentential semantics of the elided clause. 
12Stripping is also possible in comparative deletion con- 
structions. A comprehensive analysis of stripping, pseudo- 
gapping, and VP-ellipsis in such cases requires an articula- 
tion of a syntax and semantics for these constructions, which 
will be carried out in future work. 
VP-Ellipsis 
Recall from Section 2 that only in Coherent Situation 
constructions can VP-ellipsis obtain purely semantic 
antecedents without regard to constraints on structural 
parallelism, as exemplified by the voice mismatches in 
sentences (18) and (19). 
(18) # The decision was reversed by the FBI, and the 
ICC did too. \[ reverse the decision \] 
(19) In March, four fireworks manufacturers asked 
that the decision be reversed, and on Monday the 
ICC did. \[ reverse the decision \] 
These facts are also predicted by our account. In the 
case of Common Topic constructions, a suitable syn- 
tactic antecedent must be reconstructed at the site of 
the empty VP node, with the result that the anaphoric 
expression takes on its accompanying semantics. There- 
fore, VP-ellipsis is predicted to require a suitable syn- 
tactic antecedent in these scenarios. In Coherent Sit- 
uation constructions, the empty VP node is not re- 
constructed. In these cases the anaphoric expression 
is resolved on purely semantic grounds; therefore VP- 
ellipsis is only constrained to having a suitable semantic 
antecedent. 
The analysis accounts for the range of data given in 
Kehler (1993b), although one point of departure exists 
between that account and the current one with respect 
to clauses conjoined with but. In the previous account 
these cases are all classified as non-parallel, resulting in 
the prediction that they only require semantic source 
representations. In our analysis, we expect cases of pure 
contrast to pattern with the parallel class since these are 
Common Topic constructions; this is opposed to the vi- 
olated expectation use of but which indicates a Coherent 
Situation relation. The current account makes the cor- 
rect predictions; examples (20) and (21), where but has 
the contrast meaning, appear to be markedly less ac- 
ceptable than examples (22) and (23), where but has 
the violated expectation meaning: 13 
(20) ?? Clinton was introduced by John, but Mary 
didn't. \[ introduce Clinton \] 
(21) ?? This letter provoked a response from Bush, 
but Clinton didn't. \[ respond \] 
(22) Clinton was to have been introduced by someone, 
but obviously nobody did. \[ introduce Clinton \] 
(23) This letter deserves a response, but before you do, 
... \[ respond \] 
To summarize thus far, the data presented in the ear- 
lier account as well as examples that conflict with that 
analysis are all predicted by the account given here. 
As a final note, we consider the interaction between 
VP-ellipsis and gapping. The following pair of examples 
are adapted from those of Sag (1976, pg. 291): 
lZThese examples have been adapted from several in 
Kehler (1993b). 
55 
(24) :Iohn supports Clinton, and Mary $ Bush, al- 
though she doesn't know why she does. 
(25) ?? John supports Clinton, and Mary 0 Bush, and 
Fred does too. 
Sag defines an alphabeiic variance condition that cor- 
rectly predicts that sentence (25) is infelicitous, but in- 
correctly predicts that sentence (24) is also. Sag then 
suggests a weakening of his condition, with the result 
that both of the above examples are incorrectly pre- 
dicted to be acceptable; he doesn't consider a solution 
predicting the judgements as stated. 
The felicity of sentence (24) and the infelicity of sen- 
tence (25) are exactly what our account predicts. In 
example (25), the third clause is in a Common Topic 
relationship with the second (as well as the first) and 
therefore requires that the VP be reconstructed at the 
target site. However, the VP is not in a suitable form, 
as the object has been abstracted out of it (yielding 
a trace assumption). Therefore, the subsequent VP- 
ellipsis fails to be felicitous. In contrast, the conjunc- 
tion alfhough used before the third clause in example 
(24) indicates a Coherent Situation relation. Therefore, 
the VP in the third clause need not be reconstructed, 
and the subsequent semantically-based resolution of the 
anaphoric form succeeds. Thus, the apparent paradox 
between examples (24) and (25) is just what we would 
expect. 
Event Reference 
Recall that Sag and Hankamer (1984) note that whereas 
elliptical sentences such as (26a) are unacceptable due 
to a voice mismatch, similar examples with event ref- 
erential forms are much more acceptable as exemplified 
by sentence (26b): 14 
(26) a. # The decision was reversed by the FBI, and 
the ICC did too. \[ reverse the decision \] 
b. The decision was reversed by the FBI, and the 
ICC did it too. \[ reverse the decision \] 
As stated earlier, forms such as do it are anaphoric, but 
leave no empty constituents in the syntax. Therefore, 
it follows under the present account that such reference 
is successful without regard to the type of discourse 
inference employed. 
Relationship to Past Work 
The literature on ellipsis and event reference is volumi- 
nous, and so we will not attempt a comprehensive com- 
parison here. Instead, we briefly compare the current 
work to three previous studies that explicitly tie ellipsis 
14Sag and Hankamer claim that all such cases of VP- 
ellipsis require syntactic antecedents, whereas we suggest 
that in Coherent Situation relations VP-eUipsis operates 
more like their Model-Interpretive Anaphora, of which do 
it is an example. 
resolution to an account of discourse structure and co- 
herence, namely our previous account (Kehler, 1993b) 
and the accounts of Priist (1992) and Asher (1993). 
In Kehler (1993b), we presented an analysis of VP- 
ellipsis that distinguished between two types of rela- 
tionship between clauses, parallel and non-parallel. An 
architecture was presented whereby utterances were 
parsed into propositional representations which were 
subsequently integrated into a discourse model. It was 
posited that VP-ellipsis could access either proposi- 
tional or discourse model representations: in the case of 
parallel constructions, the source resided in the propo- 
sitional representation; in the case of non-parallel con- 
structions, the source had been integrated into the dis- 
course model. In Kehler (1994), we showed how this 
architecture also accounted for the facts that Levin and 
Prince noted about gapping. 
The current work improves upon that analysis in sev- 
eral respects. First, it no longer needs to be posited 
that syntactic representations disappear when inte- 
grated into the discourse model; 15 instead, syntactic 
and semantic representations co-exist. Second, various 
issues with regard to the interpretation of propositional 
representations are now rendered moot. Third, there is 
no longer a dichotomy with respect to the level of repre- 
sentation from which VP-ellipsis locates and copies an- 
tecedents. Instead, two distinct factors have been sepa- 
rated out: the resolution of missing constituents under 
Common Topic inference is purely syntactic whereas 
the resolution of anaphoric expressions in all cases is 
purely semantic; the apparent dichotomy in VP-ellipsis 
data arises out of the interaction between these different 
phenomena. Finally, the current approach more read- 
ily scales up to more complex cases. For instance, it 
was not clear in the previous account how non-parallel 
constructions embedded within parallel constructions 
would be handled, as in sentences (27a-b): 
(27) a. Clinton was introduced by John because Mary 
had refused to, and Gore was too. \[ introduced 
by John because Mary had refused to \] 
b. # Clinton was introduced by John because 
Mary had refused to, and Fred did too. \[ in- 
troduced Clinton because Mary had refused 
to \] 
The current approach accounts for these cases. 
The works of Priist (1992) and Asher (1993) pro- 
vide analyses of VP-ellipsis 16 in the context of an 
account of discourse structure and coherence. With 
l~This claim could be dispensed with in the treatment 
of VP-eUipsis, perhaps at the cost of some degree of the- 
oretical inelegance. However, this aspect was crucial for 
handling the gapping data, since the infelicity of gapping in 
non-parallel constructions hinged on there no longer being 
a propositional representation available as a source. 
16In addition, Prfist addresses gapping, and Asher ad- 
dresses event reference. 
56 
Priist utilizing a mixed representation (called syntac- 
tic/semantic structures) and Asher utilizing Discourse 
Representation Theory constructs, each defines mecha- 
nisms for determining relations such as parallelism and 
contrast, and gives constraints on resolving VP-ellipsis 
and related forms within their more general frame- 
works. However, each essentially follows Sag in requir- 
ing that elided VP representations be alphabetic vari- 
ants of their referents. This constraint rules out cases 
where VP-ellipsis obtains syntactically mismatched an- 
tecedents, such as example (19) and other non-parallel 
cases given in Kehler (1993b). It also appears that nei- 
ther approach can account for the infelicity of mixed 
gapping/VP-ellipsis cases such as sentence (25). 
Conclusion 
In this paper, we have categorized several forms of el- 
lipsis and event reference according to two features: (1) 
whether the form leaves behind an empty constituent 
in the syntax, and (2) whether the form is anaphoric 
in the semantics. We have also described two forms of 
discourse inference, namely Common Topic inference 
and Coherent Situation inference. The interaction be- 
tween the two features and the two types of discourse 
inference predicts facts concerning gapping, VP-ellipsis, 
event reference, and interclausal coherence for which it 
is otherwise difficult to account. In future work we will 
address other forms of ellipsis and event reference, as 
well as integrate a previous account of strict and sloppy 
ambiguity into this framework (Kehler, 1993a). 
Acknowledgments 
This work was supported in part by National Science 
Foundation Grant IRI-9009018, National Science Foun- 
dation Grant IRI-9350192, and a grant from the Xerox 
Corporation. I would like to thank Stuart Shieber, Bar- 
bara Grosz, Fernando Pereira, Mary Dalrymple, Candy 
Sidner, Gregory Ward, Arild Hestvik, Shalom Lappin, 
Christine Nakatani, Stanley Chen, Karen Lochbaum, 
and two anonymous reviewers for valuable discussions 
and comments on earlier drafts. 

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