Event-building through Role-filling and Anaphora Resolution 
Greg Whittemore 
Electronic Data Systems Corp. 
5951 Jefferson Street N.E. 
Albuquerque, NM 87109-3432 
greg@edsr.eds.com 
Melissa Macpherson 
Electronic Data Systems Corp. 
5951 Jefferson Street N.E. 
Albuquerque, NM 87109-3432 
melissa@edsr.eds.eom 
Greg Carlson 
Linguistics Program, University of Rochester 
Rochester, NY 
grca~uorvm.bitnet 
ABSTRACT 
In this study we map out a way to build event 
representations incrementally, using information 
which may be widely distributed across a dis- 
course. An enhanced Discourse Representation 
(Kamp, 1981) provides the vehicle both for car- 
rying open event roles through the discourse until 
they can be instantiated by NPs, and for resolving 
the reference of these otherwise problematic NPs 
by binding them to the event roles. 
INTRODUCTION 
The computational linguistics literature includes 
a wide variety of ideas about how to represent 
events in as much detail as is required for reason- 
ing about their implications. Less has been writ- 
ten about how to use information in text to incre- 
mentally build those event representations as dis- 
course progresses, especially when the identifica- 
tion of event participants and other details is dis- 
persed across a number of structures. We will be 
concerned here with providing a representational 
framework for this incremental event-building, and 
with using that representation to examine the ways 
in which reference to the internal structure of 
events contributes to discourse cohesion. That is, 
we will be interested both in the process of gleaning 
fully-specified event descriptions from continuous 
text, and in showing how individual elements of an 
event's internal structure can behave anaphorically. 
Examples of the kinds of linkages that must be 
dealt with in building representations of events 
from text follow: 
la) He was believed Co be a liar. 
b) We promised him to be truthful. 
c) He tried to keep his mouth shut. 
2a) Joe gave Pete a book to read. 
b) Joe gave Pete a book to impress him. 
c) Joe asked Pete for a book to read. 
d) I asked Joe for a book to impress Sam. 
e) Joe gave Pete the message to save 
his skin. 
3a) Joe told Pete that to err is human. 
b) He told us that to quit eould be silly. 
4a) GM will broaden collaboration with 
Lotus to make a new car. 
b) Mary thought that an argument with 
herself would be entertaining. 
c) Mary thought that a conference with 
himself would make John look silly. 
The examples in (1) are familiar cases of syntac- 
tically obligatory control; we will consider their be- 
havior to be straightforwardly and locally resolved. 
The sentences of (2) show infinitival relatives, pur- 
pose, and 'in-order-to' clauses in which control of 
the infinitive (and hence of its implicit subject) is 
sometimes clear, sometimes ambiguous. In (3), a 
subject infinitival phrase receives an unavoidably 
generic reading in one case and a non-generic but 
ambiguous reading in the other. Finally, the exam- 
ples of (4) indicate that nominalizations of events 
also have roles whose reference must be determined, 
and whose existence and identity has consequences 
for subsequent discourse. 
Aside from the sentences in (1), in which control 
is unambiguously sorted out within the sentence on 
the basis of verb type, all the examples above can 
17 
be paraphrased with equivalent multi-sentence con- 
structions in which the facts of referent-assignment 
are identical. Even more extended discourses, in- 
cluding dialogues such as that in (5), show the in- 
fluence of an instantiated situation or event over 
the assignment of referents to entities introduced 
later in the discourse. 
5) A: John has been hobbling around for 
two weeks with a sprained ankle. 
B: So what did the nurse say 
yesterday? 
A: She said that it would not be smart 
to run so soon after injuring 
himself. 
(adapted from Nishigauchi's 48, cited as 
a modification of Chao's 28) 
The distribution of event participants across 
multi-sentence discourses is sufficient to lay to rest 
any idea that the linkage is syntactically governed, 
even though the entities which provide cohesion in 
these examples are arguments which are typically 
bound syntactically. That is, it seems that initially 
unfilled thematic roles play a part in tying one sen- 
tence to the next. Event roles left unfilled after 
the operation of local syntactic processing are ap- 
parently still 'active', in some sense, and they ap- 
pear to be able to attract participants from exter- 
nal structures to fill them. Carlson and Tanenhaus 
(1988) provide psycholinguistic evidence that this 
is indeed the case; open thematic roles do appear 
to be effective as cohesion devices. 1 
Previous theories about how open roles become 
filled (mostly intra-sententially) have been based 
on notions ranging from strictly syntactic to more 
pragmatic, knowledge-based approaches. Obvi- 
ously wherever we do have what appears to be 
invariant and obligatory control, we want to ex- 
ploit a syntactic explanation. However, these cases 
1Whether it is just thematic roles, or those plus certain 
types of highly predictable adjuncts, or a wide variety of 
other types of slots which can provide the type of linking we 
are talking about is still an open question. We do assume 
that for each event we will encode not only THAT it expects 
certain arguments to be filled, but HOW it expects them to 
be filled; for instance it should be perceived that the noun 
'salesman' is a highly suitable Agent for a sale event. We 
may need to know about more than that. In particular, we 
may require metonymical devices that make discourses like 
the following possible. 
I had a hard time shopping. 
First, the parking lot was all full .... 
Coherence in this example dearly depends on being able 
to associate 'the parking lot' with 'store' and 'store' with 
the Location of the 'shopping' event. This extension is no 
different in kind, however, from the core of what we are 
proposing here. 
do not account for much of the ground that we 
need to cover. As the examples above show, even 
the syntactic position PRO often defies straightfor- 
ward control assignment, and in the case of nominal 
references to events, Williams' (1985) arguments 
against a strictly syntactic account of referent- 
assignment are convincing. Of course, there are no 
syntactic means for linking arguments with event 
descriptions intersententially. Appeals to underly- 
ing thematic role notions and/or more pragmati- 
cally governed operators then seem to hold more 
promise for the kinds of situations we are describ- 
ing. 
Given their currency above and below the sen- 
tence level, and the fact that they seem to be sen- 
sitive to both syntactic and pragmatic constraints, 
the behavior of unfilled event roles will best be ex- 
plained at the discourse level. Like other discourse 
anaphoric elements, open roles can not only receive 
their reference from distant structures, but they 
also seem to be used productively to create links 
between linguistic structures and to extend focus 
in both forward and backward directions. 
To machine-build representations of events 
whose essential components are dispersed across 
multiple structures, two key ingredients are neces- 
sary. First, the system must have knowledge about 
events and their expected participants and other 
characteristics. Given this, one can make predic- 
tions about the expectancy of arguments and the 
underlying properties they should hold. The sec- 
ond ingredient required is a means for assessing 
the mutual accessibility of discourse entities. As 
has been pointed out by various researchers, sen- 
tential structure, thematic relationships, and dis- 
course configurations all may play a part in deter- 
mining which entities must, might, and cannot be 
associated with others, and a discourse framework 
must make it possible to take all these factors into 
account in assigning reference and building repre- 
sentations of events. 
Our intent in this paper is to provide a prototype 
model of event building which is effective across 
clauses, both intra- and inter-sententially. We will 
incorporate into this representation of events a 
means for assessing accessibility of events and event 
participants for anaphoric reference, and we will 
use the representation to examine the anaphoric 
behavior of open roles. 
Event-Building Representation: We have 
chosen DRT as an overall representation scheme, 
though we will be modifying it to some extent. 
DRT has been designed to perform a variety of 
18 
tasks, including proper placement of individual 
events in an overall discourse representation and 
making it possible to indicate which event entities 
are available for future anaphoric referencing and 
what constraints hold over those entities. A typi- 
cal DR for a simple sentence is given in (6). The 
sentence, 'John gave Bill a dollar' is designated by 
the variable E1 and has associated with it a pred- 
icate calculus statement that contains the predi- 
cate, give, and argument variables V1, V2, and V3. 
The give event specification and other constraints, 
again in predicate calculus form, are contained in 
the lower portion of the DR. In the top half of the 
DR, any entities, including events, which are avail- 
able for subsequent anaphoric referencing are listed 
by their variable names. 
Vl, V2, V3, E1 
(John V1) 
(Bill V2) 
(Dolla~V3) 
El:(give (agent Vl), 
(goal V2),(theme V3)) 
6. A DR for John gave Bill a dollar. 
Our representation departs in some ways from 
the way in which the binding of anaphors is usu- 
ally shown in DRT. In versions of DRT with re- 
altime processing, whenever an NP is being pro- 
cessed, two things can happen: i) either the NP 
can be linked with a previously occurring NP and 
become anaphorically bound to it, or ii) a new ref- 
erent can be generated for the NP and posted when 
no antecedent can be found. For our purposes, it 
is convenient to include in the DR an extra tier 
which contains items which have not yet found a 
referent. ~ To designate the three parts of our DRs, 
we will use the following tier labels: 
Available Referents - AR 
Unbound Referents - UR, and 
Constraints on Referents - CR. 
For processing purposes, we will not attempt to 
immediately bind anaphors as they are encountered 
in sentences, beyond what we can get for free from 
syntactic analysis. Rather, we will initiate a two- 
stage process, with the first DR having unbound 
anaphors and the second attempting representa- 
tion of binding. In the first representation, we will 
2 A buffer of this sort may be implicit in other treatments 
of anaphora resolution; our extension is just to add it ex- 
plicitly to the DR representation. Without some such buffer 
it is not clear how one would handle sentences like 'When 
he was a kid, John was pretty goofy.' 
post unbound anaphors in UR. We will also post 
constraints for unbound items within CR to reflect 
their type, e.g. (PRO Xl), (DEFINITE X2), and 
(HE X3). When items in UR become bound (or 
when their referents are found), their bindings will 
be represented in AR, they will be crossed off from 
within UR, and a new DR will be created to reflect 
the change in status. 
We will also revise the representation of event 
descriptions in CR, by including in them implicit 
arguments for each event as well as ones which are 
explicitly realized in the sentence. Every event will 
have its underlying thematic and highly expected 
adjunctive roles posted in CR, whether the roles 
have been filled or not. These unfilled or implicit 
roles are posted as entities requiring binding, in 
UR. The constraint (IMPLICIT X) will be included 
for any open role, and for each event variable we 
will note in CR whether it was a verbal or other- 
than-verbal description. 
Example (7) contains an instance of what we 
intend. The nominalized form of an investigate 
event, marked with El, has two open slots: Agent 
and Theme, V1 and V2, respectively. E1 is posted 
as a possible referent in AR; its two implicit argu- 
ments V1 and V2 are posted in UR. Similarly, E2, 
the launch event is posted in AR, while its open 
agent role, designated by V3, is shown in UR; its 
explicit Theme is already posted in AR as El. 
AK: El, E2 
UR: V1, V2, V3 
CR: El:(investigate (Agent V1)CTheme V2)) 
E2:(launch (Agent V3) (Theme El)) 
7. A DR of the sentence An investigation was 
launched. 
We will show that because of the inclusion of 
open roles in the representation of events and on 
the UR tier, this framework for discourse repre- 
sentation makes it possible to link arguments that 
appear in a variety of structures to their respective 
events, and thus provides more predictive power for 
anaphoric resolution processes. 
Verb-based Event References: We will 
demonstrate how DRs can be used to build inter- 
clausal events by providing various examples. We 
will move from the easiest examples, those that 
have much syntactic support, to the hardest, those 
whose resolution is mostly based on pragmatic 
grounds. 
~9 
We treat the binding of the PRO subject of em- 
bedded infinitive as a case of open role filling, and 
for our purposes, such binding is fundamentally 
the same in both obligatory and non-obligatory en- 
vironments, since in every case the result is that 
open event roles are filled by arguments from ex- 
ternal sources. That is, even where control is gen- 
erated entirely within syntax, the links are con- 
strued as being the result of a cross-clause event- 
building process. The operational difference is just 
that wherever control CAN be reliably determined 
syntactically, as in the case of obligatory control 
verbs, indices between controllers and PROs will be 
in place when initial DRs are generated. 3 A typical 
DR with a controller-controllee relationship would 
appear as in (8). 
AR: Xl, El, E2 
CR: (John, Xl) 
El:(try (Agent Xl)(Goal E2)) 
E2:(leave (Agent Xl)) 
8. The DR for John tried to leave. 
In the event-building examples that we show in 
the remainder of the paper, the aim is the con- 
struction of DRs that ultimately link events and 
arguments in this same way. What is different 
about the more complicated cases is just the means 
of accomplishing the linking. In the case of non- 
obligatory control of PRO, such results may often 
require information from several levels of process- 
ing, and an adequate event-building representation 
must be able to accommodate the representation of 
all factors which are shown to be effective in pre- 
dicting that control. 
Nishigauchi (1984), for example, demonstrates 
that choice of controller can often be determined 
through knowledge of thematic roles (see also Bach, 
1982, and Dowty and Ladusaw, 1988, for their ac- 
counts). In Nishigauchi's account, control of infini- 
tival purpose clauses and infinitival relative clauses 
is primarily dependent on the presence of one of 
three thematic roles from his so-called Primary Lo- 
cation hierarchy; the idea is that a controller can 
be assigned if a Goal, Location, or Source is present 
in the sentence. Where a Goal is present, its refer- 
3Dowty and Ladusaw (1988) believe that control is gen- 
erally established via pragmatic means. They claim that it 
is pragmatic knowledge of events that enables one to gen- 
erate links between participants and events. They also be- 
lieve, however, that there are a large number of situations 
for which control has become grammaticized, and that there 
does not need to be any internal analysis in these situations 
to comprehend argument-to-event links. 
ent has precedence as controller; where Goal is not 
present, Location or Source can take control. 
The examples in (9) are indicative of the kinds 
of links that can be made via this hierarchy. In ex- 
ample (9a), the Goal 'Mary' controls the infinitival 
relative. 4 In (9b), John ends up with the book, so 
'John' is Goal, while in (9c), John as the possessor 
of the book is its Location; in both cases 'John' 
controls the infinitive. 
(9) 
a) John bought Ha.ry a book PRO to read. 
b) John bought a book PRO to read. 
c) John has a book PRO to read. 
To handle examples like (9a-c), we begin with ini- 
tial DRs that include the kind of information that 
can be expected from a syntactic/semantic parser 
that produces initial logical forms. For instance, we 
know that 'John' is the Agent and 'Mary' the Goal 
of a buy event, and that the PRO subject of 'read' 
(the Agent of the read event) has no binding. The 
object of 'read' is identified in syntax as 'book'. 5 
An initial DR for (9a) is illustrated in (10). 
AR: X1 X2 X3 E1 E2 
UR: X4 
CR: 
El:(buy (Agent Xl)(0bjeet X2)(Goal X3)) 
E2:(read (Agent X4)(Object X2)) 
(John X1) 
(book X2) 
(Mary X3) 
(PRO X4) 
(10). The initial DR for John bought Mary a book 
to read. 
At this stage, a positive check for Goal in E1 re- 
sults in the binding of the unbound variable X4 to 
X3 in AR; X4 is then canceled out of UR. Were 
there no Goal in El, a Location or Source would 
have the same effect. In a case where none of these 
roles is specified explicitly, as in example (11) (from 
Bach), it must be filled by default and/or from 
4 'Mary' is more typically interpreted as Beneficiary in 
this sentence, but Nishigauchi claims that since Mary ends 
up with the book, she is the Goal. Bach's (1982) explanation 
is similar; it is that entity which the matrix verb puts in a 
position to do the VERBing which controls the infinitive. 
SThis analysis assumes that the infinitive is recognized 
as an infinitival relative on 'book', so that it does have an 
Object gap. The infinitive could also of course he an 'in- 
order-to' clause with intransitive 'read', in which case the 
controller is the Agent of 'buy'. 
20 
context before it can bind the infinitive. In this 
case the default Goal for 'brought' is "present com- 
pany", and so the PRO subject of 'enjoy' is first 
person plural inclusive. 
(11) I brought this miserable Morgon 
to enjoy with our dinner. 
Nominal Descriptions of Events: Much discus- 
sion has focused on the extent to which the internal 
structure of NPs that have nominalized events as 
heads, e.g. 'the destruction of the city by the Ro- 
mans,' carries over the internal structure of the as- 
sociated verb-headed structure, as in 'the Romans 
destroyed the city'. The consensus is that such de- 
verbal noun phrases, while obviously semantically 
parallel in some ways, are not equivalent to ver- 
bal descriptions. In particular, semantic arguments 
associated with the nominalized form are held to 
be syntactically adjunctive in nature and entirely 
optional, even where they would be expressed as 
obligatory complements to the associated verb. 
We are interested here in cases in which nomi- 
nals representing events are linked with arguments 
that are not part of the same immediate syntac- 
tic environment. Several examples are provided in 
(12) and (13). As Higgins (1973, cf. Dowty, 1986) 
has discussed, in sentences like (12a) the subject 
of the matrix verb 'make' can be associated with 
the Agent position of an embedded nominal; there- 
fore we understand 'Romans' to be the Agent of 
'attack'. It is apparently the nature of the verb 
'make' that permits this association; 'perform' be- 
haves similarly. The verbs 'suffer' and 'undergo', 
on the other hand, link their subjects to the Theme 
or Experiencer of a nominalized event (that is, to 
what would be the expected object of the associ- 
ated verb), as shown in (12b). 
12a) The Romans made an attack on the 
Sabines. 
b) The Romans suffered a 
crippling defeat. 
Williams (1985) makes use of the notion that a 
matrix verb can impose an association between its 
own arguments and any implicit arguments of a 
controlled event noun. However as the following 
examples show, not all verbs impose association of 
arguments to the degree that 'perform' and 'un- 
dergo' do. A verb may show some tendency toward 
association between Agents, as 'schedule' does in 
(13a), but be open to a realignment of matrix sub- 
ject with some other more focused role in other 
environments, as in (13b). Some may have such 
a slight tendency to associate arguments in a par- 
ticular way that it can be disrupted by syntactic 
structure, as in (13c) and (13d). In (13c) Sam may 
or may not be a party himself to the agreement, 
but in (13d) he is probably not involved. 
(13a) John scheduled a takeover/meeting. 
b) John scheduled a haircut/a checkup. 
c) Sam negotiated an agreement. 
d) An agreement was negotiated 
by Sam. 
What is necessary in order to sort this out is 
a working framework within which these tenden- 
cies can be represented and their interactions with 
other factors tracked. Where the tendency towards 
association is as strong as it is for 'make', which is 
considered to be semantically "bleached" in such 
constructions as make an attempt, make an ar- 
rangement, make a promise, make an attack (that 
is, it could be said to have become just a mech- 
anism for linking matrix subject to object event), 
our representation will allow for an early linking at 
the level of syntax. For the general run of cases 
where an event noun is the object of a matrix verb, 
as in (13a-d), we must rely on our knowledge of typ- 
ical interactions between events in order to decide 
what the linking between matrix subject and em- 
bedded event might be. The interaction between 
the AR and the UR tiers of the DR, along with 
constraints on variables of both types, allows us to 
manipulate the association as may seem appropri- 
ate, with as much knowledge as we have at the time 
of linking. 
Cross-Sentence Event-building: As we men- 
tioned earlier, the linking phenomena we are ex- 
amining hold across, as well as within sentences. 
Discourse (14) is provided as an example of a dis- 
course in which an open role is filled in a subsequent 
sentence. In the first sentence, there are actually 
several open roles. Left unfilled are (at least) the 
roles Source and Exchange. With the DR struc- 
turing we have chosen, an initial DR for the first 
sentence of (14) would be built as in (15). The main 
thing to note in (15) is that the open role variables, 
are Z1 and Q1, the Source and the Exchange, have 
been posted in UR. 
(14a) Pete bought a car. 
b) The salesman was a real jerk. 
21 
(ls) 
AR: EI,XI,YI 
UR: Zl O1 
CR: (Pete Xl) 
(car Y1) 
El:(buy (Agent Xl), (Theme Y1), 
(Source ZI), (Exchange Ol)) 
(implicit Z1) 
(implicit ql) 
The initial DR. for the second sentence of (14) is 
in (16a). The variable X2, representing 'the sales- 
man', has been posted in the unresolved NP buffer, 
and X2 will be the first thing to be resolved by way 
of anaphora operators. 
The anaphoric processes invoked at this point 
would be much like what has been promoted else- 
where. A variety of factors would come into play, 
including looking at basic semantic characteristics, 
centering, etc. We would also want to provide a 
means for ordering available referents as they are 
placed in AR. in terms of their forward focusing 
character (Grosz, Joshi, and Weinstein, 1983). 
For 'the salesman', the previously occurring dis- 
course entities that are available as referents are El, 
Xl, and Y1 in the previous AR., and Z1 and Q1 in 
the previous UR. The possible referent Xl, 'Pete', 
ranks as a possible candidate but not a very likely 
one, since if Pete were to be referred to in a subse- 
quent sentence it would more likely be done via a 
personal pronoun. The other available referent, Y1, 
the 'car', is semantically unlikely and is not con- 
sidered a good choice. A search is then made into 
the previous UR.. The Source Z1, in this instance, 
would be a highly likely choice, since any seman- 
tic qualities that would accompany 'the salesman' 
would fit those of the Source of a buy event. 
It has been reported in previous studies that def- 
inite NPs often have no clear antecedent. For in- 
stance, 363 out of 649 definite NPs found in a study 
of corpus of dialogues (Brunner, Ferrara, and Whit- 
temore, 1990) had no direct linguistic antecedents. 
53% of the 363 definite NPs had semantically in- 
ferrable antecedents, where definite NPs were used 
to refer to attributes of antecedents and the like, 
but not to antecedents themselves. Apparently, 
definite NPs function to focus on some partial as- 
pect of an antecedent or topic and not necessarily 
to refer directly to it as a whole. 6 Following the 
6The other 47% were reported to have no clear an- 
tecedents, and were only 'topically' tied to the context. It 
might prove beneficial to re-examine these true orphans and 
see if any of these refer back to open roles. 
line of reasoning that one could take from these 
findings, it could be the case that there is actually 
a preference for definite NPs to refer back to open 
roles, since they represent particular points of focus 
or sub-components of events. 
'Salesman', via the variable X2, would then get 
bound to the buy event and a second DR. with no 
unresolved anaphora would be returned, as shown 
in (16b). 
(16a) 
AR: E2 
UR: X2 
CR: (Salesman X2) 
(definite X2) 
E2:(IS X2 real-jerk) 
(16b) 
AR: X2, E2 
UR: 
CR: (Salesman X2) 
(definite X2) 
E2:(IS X2 real-jerk) 
Similarly, the DR for the first sentence would 
need modification since now the open Source role, 
represented as Z1, would need to be bound to X2, 
'the salesman' (this updated binding is not shown). 
Limits on Linking: There are limits on the 
kinds of linking that can be effected between event 
descriptions and fillers for open roles. For instance, 
note that the open slot in the example above does 
not seem to be available for pronominal reference. 
If (14b) is replaced with 'He was a real jerk,' the 
sequence of sentences makes no sense (or at least 
we would have to say that the same role is not 
accessed). This restriction appears to be true in 
general for pronominal reference into event descrip- 
tions, as the following examples show: 
• I was attacked. *He was enormous. 
• We unloaded the car. *They \[the suitcases\] 
were very heavy. 
• This borrowing has got to stop. *They \[the 
borrowed things\] get left all over the place. 
An event description itself, as a whole, nomi- 
nal or verbal, may function as an antecedent for 
22 
subsequent anaphoric reference, including pronom- 
inal reference ('I went swimming. It was horrible.'). 
It is just pronominal reference INTO an event de- 
scription, especially a verbal one, which seems to be 
blocked. The event described in (17a) below cannot 
typically be elaborated upon by (l?ai). However, 
(17ai) is fine as a continuation if (17aii), in which 
the event is nominalized, comes between. (17b), in 
which the agree event is referred to nominally, can 
be followed by (17bi), (17bii) or both. 
(17) 
a) Bob finally agreed eith Joe. 
i) *It was to not fight anymore. 
ii) The agreement ,as negotiated 
by Sam. 
b) Bob and Joe finally made an agreement. 
i) It was to not fight anymore. 
ii) It/The agreement was negotiated 
by Sam. 
c) *It was between Bob and Sam. 
In our representation the posting of event de- 
scriptions, verbal and nominal, in AR, accounts 
for the fact that each can be linked to by a sub- 
sequent pronominal element. Our intuition is that 
in order to be completely accessible as a referent, 
however, an entity must have not only a semantic 
but also a phonological realization; since open roles 
are merely implicit until they are bound, it is pre- 
dictable that there would be a difference in their 
accessibility. For this reason we post open roles 
only in UR, not in AR, and in our framework this 
blocks pronominal access to them. 
As for the fact that nominalizing an event seems 
to ease the restrictions on referring into it by means 
of a pronoun (as in the (17ai-ii) examples), our 
guess is that in these cases the pronominal refer- 
ence is actually to the event as a thing, and that the 
apparent elaboration of roles is allowed by the same 
mechanisms that allow addition of other adjuncts 
to nominals, as in 'I really enjoyed my vacation. It 
was in Texas in July.' In any case our tagging of 
event variables in CR as nominal or verbal allows 
this distinction to be taken into account. 
The idea of role slots which are canceled from UR 
as they are bound explains another restriction on 
the ways in which events can be elaborated. (17c) 
above cannot appropriately follow either (171) or 
(17b), because we already know from either that 
the agreement was between Bob and Joe. Further, 
if (17bii) follows (17b), then we know that Sam 
is not himself a participant in the agreement he 
negotiated, because we already know from (17b) 
that the agreenaent was between Bob and Joe. In 
each of these cases, the open role in question will 
have been canceled out of UR by binding to other 
entities before the new anaphoric elements come 
along, and so there is no possibility of filling a role 
twice. 
Hard Cases: Finally, we offer a few comments 
on a "pretty hard" and a "really hard" example, 
given in (18) and (19). These are revised versions 
of the discourse given in (5). The task in both cases 
is to bind the referent 'John', which appears in the 
first sentence, to the Agent slot of 'run', which is 
in the second sentence. 
(18) 
John has been hobbling around 
on a sprained ankle. 
Today, the nurse said it would be best 
not to run for teo weeks. 
(19) 
John has been hobbling around 
on a sprained ankle. 
Today, the nurse told his mother it would 
be best not to run for two weeks. 
To resolve these examples, we can employ two 
tactics. First, we will impose a thematic role asso- 
ciation between the Addressee of a say event and 
the Agent of embedded agentless verbs that denote 
advice. Secondly, we will use the notion of open 
implicit roles in DtLs to obtain a filler for the open 
Addressee role in the say/tell event. 7 
With these two notions in place, we can easily 
resolve (18). (18)'s context provides only one pos- 
sible candidate for the open Addressee role, namely 
'John' (that is, if we disregard the speaker of the 
utterance). Once 'John' is used to fill that role, we 
can link 'John also, through the default thematic 
role association, to the Agent slot for 'run'. 
(19), however shows that the situation can be 
more complicated. There is no open Addressee 
role in (19); the explicit Addressee is 'his mother'. 
By the process above, then, 'his mother' would be 
linked to the Agent slot of 'run', which of course 
is incorrect. We do not have a perfect explanation 
for why (19) is different from (18), other than that 
John's mother is not the ultimate Addressee. That 
is, a mechanism is needed that can determine that 
John's mother transfers the advice on to the per- 
son who needs it, namely the ailing person, namely 
John. Even if such a complicated scenario is the 
ZA more general form of the first step would be a the- 
matic role reasoning device that permits PROs to be linked 
with those entities which are most eligible to carry out the 
action of the subjectless infinitive. This formulation would 
be in the spirit of Bach, 1982. 
23 
correct one, we believe that our combined thematic 
role/discourse representation would provide a plat- 
form upon which one could make use of such prag- 
matic information. 
Conclusion: Our stated task was to provide 
a vehicle for constructing event representations 
which have roles that are not filled by local syntac- 
tic means. DRT is a natural vehicle for~this kind of 
exercise, given certain extensions. The major ex- 
tension is the posting of open event (thematic) roles 
as potential anchors for subsequent reference. In 
other words we are treating open roles as a type of 
anaphor. Where roles integral to an understanding 
of an event are not immediately filled on the basis 
of local syntax, we hypothesize that they should 
be posted nonetheless as not-yet-instantiated slots. 
We have added a tier to the conventional notion of 
a DR to accommodate this posting. 
Our experiments with this representation have 
shown how information from various levels of pro- 
cessing can be brought together in event building. 
This framework also allows us to discover limits on 
linking phenomena; in particular, it naturally illus- 
trates the inaccessibility of open roles to pronomi- 
nal reference, and the tendency for definite NPs to 
link to substructures within an event. 
ACKNOWLEDGEMENTS 
We would like to note that the idea of using DRs 
as a means for building events across clauses came 
from a comment by Rich Thomason, cited in Dowty 
(1986:32): "Rich Thomason (p.c.) has suggested to 
me that a very natural way to construct a theory 
of event anaphora would be via Discourse Repre- 
sentation Theory." Thomason was addressing (we 
think) the notion of referring to events via nominal- 
izations. We just extended the idea of using DRT 
to construct events across clauses to also include 
those denoted by verbs. 
\[3\] Dowty, D. and Ladusaw, W. 1988. Toward a 
Nongrammatical Account of Thematic Roles, in 
Volume 21 of SYNTAX AND SEMANTICS, pgs. 
61-73. 
\[4\] Grosz, B., Joshi, A., and Weinstein, S. 1983. 
Providing a Unified Account of Definite Noun 
Phrases in Discourse. SRI Technical note ~292. 
\[5\] Kamp, H. 1981. A Theory of Truth and Se- 
mantic Representation, in J. Groenendijk, T. 
Jannsen, and M. Stokhof, (eds.). FORMAL 
METHODS IN THE STUDY OF LANGUAGE. 
\[6\] Nishigauchi, T. 1984. Control and the Thematic 
Domain. LANGUAGE, Volume 60, no. 2, pgs. 
215-250. 
\[7\] Williams, E. 1980. Predication. LINGUISTIC 
INQUIRY, Volume 11, no. 1, pgs. 203-238. 
\[8\] Williams, E. 1985. PRO and Subject of NP. 
NATURAL LANGUAGE AND LINGUISTIC 
THEORY, Volume 3, no. 3, pgs. 297-315. 
References 
\[1\] Carlson, G. and Tanenhaus, M. 1988. Thematic 
Roles and Language Comprehension. THE- 
MATIC RELATIONS, VOLUME 21 OF SYN- 
TAX AND SEMANTICS, pgs. 263-291. 
\[2\] Dowty, D. 1986. On the Semantic Content of 
the Notion "Thematic Role". paper presented at 
the University of Massachusetts conference on 
Property Theory, Type Theory, and Semantics, 
March 13-16, 1986. 
24 
