GETTING AT DISCOURSE REFERENTS 
Rebecca J. Passonneau 
UNISYS, Paoli Research Center 
P.O. Box 517, Paoli, PA 19301, USA 
ABSTRACT 
I examine how discourse anaphoric uses of the 
definite pronoun it contrast with similar uses of 
the demonstrative pronoun thai. Their distinct 
contexts of use are characterized in terms of two 
contextual features--perslstence of grammati- 
cal subject and persistence of gr,~mmatical 
form--which together demonstrate very clearly 
the interrelation among lexical choice, grammati- 
cal choices and the dimension of time in signalling 
the dynamic attentional state of a discourse. 
1 Introduction 
Languages vary in the number and kinds of gram- 
matical distinctions encoded in their nominal and 
pronominal systems. Language specific means 
for explicitly mentioning and re-mentioning dis- 
course entities constrain what Grosz and Sidner 
refer to as the linguistic structure of discourse \[2\]. 
This in turn constrains the ways in which dis- 
course participants can exploit linguistic structure 
for indicating or inferring attentional state. At- 
tentional state, Grosz and Sidner's term for the 
dynamic representation of the participants' focus 
of attention \[2\], represents--among other things- 
which discourse entities are currently most salient. 
One function of attentional state is to help resolve 
pronominal references. English has a relatively 
impoverished set of definite pronouns in which 
gender is relevant only in the 3rd person singu- 
lar, and where number---a fairly universal nominal 
category--is not relevant in the 2nd person. Yet 
even within the English pronominal system, there 
is a semantic contrast that provides language users 
with alternative means for accessing the same pre- 
viously mentioned entities, therefore providing in- 
vestigators of language with an opportunity to ex- 
plore how distinct lexicogrammatical features cor- 
relate with distinct attentional processes. This 
is the contrast between demonstrative and non- 
demonstrative pronouns. In this paper I examine 
how certain uses of the singular definite pronoun it 
contrast with similar uses of the singular demon- 
strative pronoun that. 
I present evidence that the two pronouns it and 
that have pragmatically distinct contexts of use 
that can be characterized in terms of a remarkably 
simple set of preconditions. First, in §2 1 delineate 
the precise nature of the comparison made here. In 
§3.1, I describe the methods I used to collect and 
analyze a set of data drawn from ordinary con- 
versational interactions. The result of my statisti- 
cal analysis was a single, highly significant multi- 
dimensional distributional model, showing lexieai 
choice to be predicted by two features of the lo- 
cal context. In §3.2, I summarize the statistical 
results. They were strikingly clearcut, and pro- 
vide confirmation that grammatical choices made 
by participants in a dialogue prior to a particular 
point in time correlate with lexical choice of either 
participant at that time. 
Of over a dozen different variables that were 
examined, two alone turned out to have enor- 
mons predictive power in distinguishing between 
the typical contexts for the two pronouns. Very 
briefly, the first variable, persistence of gram- 
matical subject, indicates whether both the an- 
tecedent and pronoun were subjects of their re- 
spective clauses. The second, persistence of 
grammatical form, indicates whether the an- 
tecedent was a single word phrase or a multi- 
word phrase, and if the latter, whether the phrase 
was syntactically more clause-like or more noun- 
like. Both variables point up the significance of 
the temporal dimension of discourse in two ways. 
The first has to do with the evanescence of sur- 
face syntactic form--the two features pertaining 
to the grammatical means used to refer to entities 
are relevant only for a short time, namely across 
two co-references \[17\]. The second has to do with 
the dual nature of referring expressions--as noted 
by Isard they are constrained by the prior con- 
text but immediately alter the contezt and become 
part of it \[3\] \[18\]. In §4 I discuss how the contrast 
between the definite and demonstrative pronouns 
is constrained by the local discourse context, and 
51 
how the constraining features of the local context 
in combination with the lexical contrast provides 
evidence about modelling the attentional state of 
discourse. 
2 Comparability of it and that 
Previous work has related the discourse deictic 
uses of that to the global segmental structure of 
discourse, and tied the contrast between it and 
that to the distinction between units of informa- 
tion introduced at the level of discourse segments 
versus units of information introduced at the level 
of the constituent structure of sentences \[8\] \[12\] 
\[18\]. This paper deals only with the latter cate- 
gory. That is, I am concerned with entities that 
are evoked into the discourse model by explicit 
mentions, i.e., noun phrases \[19\] or other intra- 
sentential constituents, and with the difference be- 
tween accessing these referents via the definite ver- 
sus the demonstrative pronoun. Thus the data re- 
ported on here are restricted to cases where one of 
these pronouns has occurred with an explicit lin- 
guistic antecedent that is a syntactic argument. 1 
A pronoun's antecedent was taken to be a prior 
linguistic expression evoking (or re-evoking) a dis- 
course entity that provided a pronoun's referent. 
The two expressions were not constrained to be 
strictly coreferential since a wide variety of seman- 
tic relationships may hold between cospecifying 
expressions \[I\] \[16\] \[19\]. 
Syntactically it and that have very similar-- 
though not identical--privileges of occurrence. 2 
The following bullets briefly summarize their syn- 
tactic differences. 
• that, but not it, is categorially ambiguous, oc- 
curring either as a determiner or as an inde- 
pendent pronoun 
• it, but not that, has a reflexive and a posses- 
sive form ( itself/*thatsel~,, its/*thats) 
• it, but not that, may occur in prepositional 
phrases where the pronoun in the PP corefers 
with a c-commanding NP (the table with a 
drawer in itpthat) 
x Pronouns whose antecedents were independent tensed 
clauses or clausal conjuncts were excluded from considera- 
tion here; I reported on a much larger class of contexts in 
t12   42;ext,. ch  . mmate betw n thcm. .t _ 
tically occurred very rarely in my data. 
• it, but not that, can be used non-referentially 
( it/*that is raining; it/*that is hard to find an 
honest politician) 
These differences, though they may ultimately 
pertain to the phenomena presented here, won't be 
discussed further. In general, that can occur with 
the same syntactic types of antecedents with which 
it occurs. Thus, apart from prosodic differences-- 
which were not considered here---the two pronouns 
are extremely comparable semantically as well as 
syntactically. Both pronouns are 3rd person, non- 
animate, and singular. They are thus primarily 
distinguished by the semantic feature of demon- 
strativity. 
An unforeseen but interesting fact is that the 
proximal demonstrative this occurred very rarely. 
So the relevant semantic contrast was that be- 
tween definiteness and demonstrativity, and did 
not include the proximal/non-proximal contrast 
associated with this versus that. While I had 
originally planned to investigate the contrast be- 
tween the two demonstrative pronominals as well, 
there were only 8 tokens of this out of ,,-700 pro- 
nouns whose antecedents were sentence internal 
arguments. This strongly suggests that however 
the attentional space of discourse entities is struc- 
tured, it is not as differentiated as in the spatio- 
temporal domain, where the contrast between this 
and that is apparently more relevant. With respect 
to the contexts examined here, the proximal/non- 
proximal contrast between this and that is irrele- 
vant. 
A stretch of discourse evokes a set of discourse 
entities, some of which can be accessed pronomi- 
nally. Of these, some can be accessed by it, and 
some can be accessed by that. The data I present 
suggest that the availability of focussed entities for 
definite and demonstrative pronominal reference 
differs, and that the consequences on the subse- 
quent attentional state also differs. The conditions 
on and consequences of speaker choice of it or that 
must be pragmatic, and further, it is likely that 
the choice pertains to attentional state, since both 
pronominaiization and demonstrativity play such 
a large role in indicating the attentional status of 
their referents (cf. \[8\], \[15\], \[18\]). 
The following excerpts from my conversational 
data illustrate the syntactic variety of the pro- 
nouns' antecedents, and give a sense as well that 
substituting one pronoun for another sometimes 
results in an equally natural sounding discourse, 
with the difference being a very subtle one, as 
52 
in 2. 3 Occasionally, the substitution creates dis- 
course that is pragmatically odd, as in 6. 
1. A: so \[you plan to\] work for a while, save 
some money, travel--B: save SOME MONEY 
and then blow IT (/THAT) off and then go 
to school 
2. what does NOTORIETY mean to you, where 
does THAT (/IT) put you 
3. I didn't really want TO (PAUSE) TEACH PEO- 
PLE, THAT (/IT) wasn't the main focus 
4. so in some ways, I'd like TO BE MY OWN BOSS, 
so THAT (/IT)'s something that in some way 
appeals to me very much 
5. the drawback is THAT I'M ON CALL 24 HOURS 
A DAY but IT (/THAT) also means I get dif- 
ferent periods of time off 
6. I don't think EACH SITUATION IS INHERENTLY 
DIFFERENT FROM THE OTHER, at least, THAT 
(/IT)'s not the way I look at it 
In this paper, I focus on the linguistic features 
of the local context, i.e., the context containing a 
pronoun token and its antecedent, in order to in- 
vestigate the relationship between the pronominal 
features of demonstrativity and definiteness and 
the local attentional state of a discourse. 
3 Statistical Analysis of the 
Conversational Data 
3.1 Method 
Psychologists and sociologists studying face-to- 
face interaction have argued that the baseline of 
interactive behavior is dyadic rather than monadic 
\[4\] \[9\]; similarly, in understanding how speak- 
ers cooperatively construct a discourse, the base- 
line behavior must be dialogic rather than mono- 
logic. The analytic methods employed here were 
adapted from those used in studying social inter- 
action among individuals. I analyzed the local 
context of lexical choice between it and that in 
four career-counseling interviews. The interviews 
3The relevant pronoun tokens and their antecedents 
appear in CAPS, and the substituted pronoun appears in 
parentheses to the right of the original. A: and B: are used 
to distinguish two speakers, where relevant. Text enclosed 
in brackets was added by the author to clarify the context. 
took place in a college career-counseling office, and 
were not staged. The final corpus consisted of 
over 3 1/2 hours of videotaped conversation be- 
tween counselors and students. This provided an 
excellent source of data, with the speakers con- 
tributing tokens of it/that at the rate of roughly 1 
in every 2 sentences, or a total of 1,183 tokens in 
all. Nearly all of these were indexed and coded for 
16 contextual variables characterizing the linguis- 
tic structure of the local context. 4 These variables 
fell into two classes: those pertaining to the rdN- 
EAR ORGANIZATION OF DISCOURSE, or to the re- 
spective locations of the antecedent and pronoun~ 5 
and those pertaining to the SYNTACTIC FORM of 
the antecedent expression. 
Statistical analysis was used as a discovery pro- 
cedure for finding the strongest determinants of 
lexical choice, rather than to test a particular hy- 
pothesis. The goal was to find the best \]it between 
the contextual variables and lexical choice, i.e., 
to include in a final statistical model only those 
variables which were highly predictive. I used log- 
linear statistical methods to construct a single best 
multi-dimensional model; log-linear analysis per- 
mits the use of the x-square statistic for greater 
than 2-dimensional tables. This is advantageous, 
because multi-dimensionality imposes more con- 
straints on the statistical model, and is thus even 
more reliable than 2-dimensional tables in reveal- 
ing non-chance correlations. In addition to multi- 
dimensionality, three other criteria guided the se- 
lection of the best \]it: a statistically significant 
probability for the table, meaning a probability of 
5.0% or lower; statistical independence of the pre- 
dictive variables from one another, i.e., that they 
represented truly distinct phenomena, rather than 
overlapping factors; and finally, that the distribu- 
tional patterns were the same for each individual 
speaker and for each separate conversation, in or- 
der to justify pooling the data into a single set. 6 
The antecedents of some of the pronouns oc- 
curred in the interlocutor's speech, but change of 
4Certain repetitions, e.g., false starts, were excluded 
from consideration; cf. chapter 2 of 1131 
SLacation was construed very abstractly, and included, 
e.g., measures of whether the antecedent and pronoun were 
in the same, adjacent, or more distant sentences; how 
deeply embedded syntactically the antecedent and pronoun 
were; how many referential expres~ons with the same or 
conflicting semantic features of person, number and gender 
intervened between the pronoun and its antecedent; and 
their respective grammatical roles \[131. 
6The reliability of the data was tested by comparing 
within- and across-subjects statistical measures; i.e., I took 
into account the data for the conversations as a whole, each 
individual conversation, and each individual speaker \[13\]. 
53 
IT Form of Gram'l 
Ant't Roles 
Pronoun Subj-Subj 
Other 
NP Subj-Subj 
Other 
Nou-NP Subj-Subj 
Arg Other 
Other Subj-Subj 
Other 
Column Totals 
147 
110 
90 
18 
25 
18 
416 
Absolute Distributions 
THAT Row 
Totals 
31 178 
54 164 
6 24 
88 178 
3 6 
66 91 
2 7 
12 30 
262 678 
Main and Interaction Effects 
Source 
Intercept 
Form of Antecedent 
Grammatical Roles 
Likelihood Ratio 
Degrees of X- Proba- 
Freedom Square bility 
1 12.71 0.0004 
3 39.37 0.0001 
1 16.87 0.0001 
:3 0.35 0.9509 
Table I: A Multi-Dimensional Statistical Model of 
Lexical Choice 
speaker within the local context had no effect on 
lexical choice, either alone, or in concert with other 
factors. Before pooling the data from all con- 
versations and all individual speakers into a sin- 
gle population, the variability across conversations 
and speakers was tested and found to be insignif- 
icant. Thus the results presented below represent 
a speaker behavior--lexical choice of pronoun m 
that is extraordinarily consistent across speakers, 
that is independent of whether a pronoun and its 
antecedent occurred in the same speaker's turn, 
independent of individual speaker and even of in- 
dividual conversation. Consequently, it is justifi- 
able to assume that the factors found to predict 
lexical choice pertain to communicatively relevant 
purposes. In other words, whatever these factors 
are, they presumably pertain not only to models 
of speech production, but also to models of speech 
comprehension. 
3.2 Results 
Table 1 gives the distribution of pronouns across 
the relevant contexts and gives the probabilities 
and x-squares for the two contextual variables 
and their intercept, i.e., the interaction between 
them/ The very low probability of 0.04% for 
7Note that the 4th category of Antecedent--Other-- 
includes a mixture of atypical arguments, primarily adver- 
bial in nature, like the adverbial argument of go in go far. 
I Form Subsequen i Pronoun 
of Subject Non-Subject 
Antecedent IT I THAT IT I THAT 
Pronominal 147 31 39 19 
Subject 96.0 48.7 48•7 42.4 
27.1 6.4 1.9 12.9 
Pronominal 37 21 34 14 
Non-Subject 43.1 21.9 21.9 19.1 
.9 .0 6.7 1•3 
NP 18 6 Ii 10 
Subject 18.3 9.3 9.3 8.1 
.0 1.1 .3 •1 
NP 43 33 36 45 
Non-Subject 63.9 32.4 32.4 28.2 
6.8 .0 .4 10.0 
Non-NP 8 5 1 1 
Subject 6.1 3.1 3.1 2.7 
.6 1.2 1.4 I.I 
Non-NP 23 44 19 33 
Non-Subject 48.4 24.6 24.6 21.4 
13.3 15.3 1.3 6.3 
Table x-Square 116.3 
Degrees of Freedom 7 
Probability 0.001 
Table 2: A Two-Way Distributional View of the 
Data, showing Absolute Frequency, Expected Fre- 
quency, and x-squares for each Cell 
the intercept indicates that the two variables axe 
clearly independent, or in other words, repre- 
sent two distinct contexts. The exceedingly low 
probabilities of 0.01% for the contextual variables 
and the highly significant table x-square (i.e., 
close to 1) indicate that the model is extremely 
significant, s The correlation between the depen- 
dent dimension of lexical choice and the two inde- 
pendent dimensions, persistence of grnmmat- 
ical subject and persistence of grammati- 
cal form, presents an intuitively very satisfying 
view--yet not an obvious one a priori---of how 
all three variables conspire together to convey the 
current attentional status of a discourse referent• 
First I will summarize the effects of the two con- 
textual variables one at a time. Then I will review 
the distributionally significant facts as a whole. 
First Dimension: Persistence of Grammat- 
ical Subject. The first dimension of the model 
is binary and the two contexts it defines are in 
diametric opposition to one another; it was likely 
SThe cutoff is generally 5%; 1% is deemed to be very 
significant. 
54 
to occur in exactly one of the two contexts, and 
that was likely to occur in the opposing context. If 
both referring expressions were subjects, then the 
lexical choice was far more likely to be it than that. 
All it took for the balance to swing in favor of the 
demonstrative was for either the pronoun itself or 
for its antecedent to be a non-subject. The two 
relevant contexts, then are: 
• those in which both the antecedent and the 
target pronoun are syntactic subjects; =~ IT 
• all other contexts. =~ THAT 
Parallelism has sometimes been suggested as an 
organizing factor across clauses. It is certainly a 
strong stylistic device, but did not make a strong 
enough independent contribution to the statistical 
model to be included as a distinct variable. To 
repeat, the crucial factor was found to be that 
both expressions were subjects, not that both had 
the same grammatical function in their respective 
clauses. In §4.1 I will review the relationship of 
these results to the centering literature \[I\] \[5\] \[6\]. 
Second Dimension: Persistence of Gram- 
matical Form. While many grammatical dis- 
tinctions among sentence constituents are possi- 
ble, the syntactic form of a pronoun's antecedent 
correlated with the choice between it and that in 
the following very specific way. The 3 discriminat- 
ing contexts were where the antecedent was: 
• any pronoun--the lexical choice for an an- 
tecedent pronoun had no effect on the lexical 
choice of the subsequent pronoun; =~ IT 
• a canonical ~P headed by a noun (including 
nominalizations); =~ IT or THAT 
• and all other types of constituents. =~ THAT 
The latter category included gerundives, infiniti- 
val expressions, and embedded finite clauses. 9 For 
contexts with a pronominal antecedent, the lexical 
choice was far more likely to be it. For canonical 
NP antecedents, it and that were equally likely, re- 
gardless of the type of head. For other types of 
constituents, that was far more likely. Thus there 
are two opposing contexts and one which doesn't 
discriminate between the two pronouns, i.e., a con- 
text in which the opposition is neutralized. 
°Cf. \[14\] for & detailed discussion of how the precise 
dividing llne between types of antecedents was determined. 
The dynamic component of this dimension is 
that it indicates, for a consecutive pair of co- 
specifying expressions, whether there has been a 
shift towards a surface form that is syntactically 
more compact and semantically less explicit, and 
if so, how great a shift. In the first context, where 
the antecedent is already pronominal, there is no 
shift, and it has a much higher probability of oc- 
currence than that. The context in which there is a 
shift from a lexical NP to a phrasal NP, i.e., a shift 
from a reduced form to an unreduced one, but no 
categorial shift, doesn't discriminate between the 
two pronouns. The context favoring that is the 
one in which there is not only a shift from a single 
word to a multi-word phrase, but also a change in 
the categorial status of the phrase from a non-NP 
constituent to a lexical NP. 
Full 3-way model. Table 2 displays the data in 
a finer-grained two-dimensionai x-square table in 
order to show separately all 4 of the possible out- 
comes, i.e., it or that as a subject or non-subject. 
In this table, the row headings represent the an- 
tecedent's form and grammatical role; the column 
headings represent the lexical choice and gram- 
matical role of the subsequent pronominal expres- 
sion. Each cell of the table indicates the absolute 
frequency, the expected frequency given a non- 
chance distribution, and the cell x-square, with 
the latter in boldface type to indicate the signif- 
icant cells. This is a somewhat more perspicu- 
ous view of the data because it can be displayed 
schematically in terms of initial states, final states, 
and enhanced, suppressed or neutral transitions, 
as in Fig. 1. However, it is also a somewhat mis- 
leading transformation of the 3-dimensional view 
given in table 1, because it suggests that the gram- 
matical role of a pronoun and that of its an- 
tecedent are independent factors. Since the sta- 
tistical model shown in table I is actually the best 
fit of the data, better than other models that were 
tested in which the grammatical role of each ex- 
pression was treated separately \[13\], it is crucial to 
recognize that the statistically significant factor is 
the pair-wise comparison of subject status. 
Large cell x-squares in Table 2 indicate the sig- 
nificant contexts, and a comparison of the absolute 
and expected frequencies in these cells indicate 
whether the context is significantly frequent or sig- 
nificantly infrequent. Thus there ar~ 3 types of 
cells in the table representing the contexts of lexi- 
ca\] choice as chance events, as enhanced events, or 
as suppressed events. In Fig. 1, I have translated 
55 
1. Pro-Subj ~" IT-Subj 
2. -I THAT-Subj 
3. IT-NonSubj 
4. -I THAT-NonSubj 
5. Pro-NonSubj IT-Subj 
6. THAT-Subj 
7. I- IT-NonSubj 
8. THAT-NonSubj 
9. NP-Subj IT-Subj 
10. THAT-Subj 
11. IT-NonSubj 
12. THAT-NonSubj 
13. NP-NonSubj -~ IT-Subj 
14. THAT-Subj 
15. IT-NonSubj 
16. t- THAT-NonSubj 
17. NonNP-Subj 
18. 
19. 
20. 
21. NonNP-NonSubj -I IT-Subj 
22. I- THAT-Subj 
23. IT-NonSubj 
24. I- THAT-NonSubj 
Figure 1: Schematic Representation of Table 2 as 
a set of State Transitions 
the table into a set of 3 types of state transitions. 
Initial states are in the left column and final states 
in the right one. The 3 types of transition are one 
which is unaffected by the contrast between it and 
that (no symbol), one which is enhanced (~-), and 
one which is suppressed (-t). The initial states in 
boldface indicate for each antecedent type which 
of the two grammatical role states was more likely, 
subject or non-subject. Absence of final states for 
the nonNP-Subj initial state indicates that this set 
of contexts is extremely rare. In the following sec- 
tion, I discuss the relation of these events to an 
abstract model of attentional state. 
4 Discussion 
The outcome of this study is not a model of at- 
tentionai processes per #e, but rather, a set of fac- 
tors pertaining to attentional structure that elu- 
cidates the shifting functions of the demonstra- 
tive pronoun in English discourse. The particular 
function served by that seems to depend on what 
functional contrasts are available given the current 
attentionai state. 
It is most useful to think of the data in terms 
of two major categories of phenomena. The first 
category is where a discourse entity has already 
been mentioned pronominally. In this case, main- 
tenance of reference in subject grammatical role is 
a particularly signficant determinant of the choice 
between it and that. This effect is discussed in 
§4.1 in relation to the notion of centering. The 
second category is where a discourse entity most 
recently evoked by a multi-word phrase is subse- 
quently referenced by a pronoun. While gram- 
matical role is relevant here, its relevance seems 
to depend on a more salient distinction pertaining 
to the syntactico-semantic type of the discourse 
entity, as discussed in §4.2. 
4.1 Definite/Demonstrative 
Pronouns and Centering 
The literature on attentionai state has shown that 
both pronominalization and grammatical role af- 
fect the attentionai status of a discourse entity. In 
this section I will show how the use of the definite 
pronoun it conforms in particular to the predic- 
tions made by Kameyaxna \[6\] \[5\] regarding canon- 
icai and non-canonical center-retention, and that 
the demonstrative pronoun is incompatible with 
center-retention. 
The centering model predicts that an utterance 
will contain a referent that is distinguished as the 
backward looking center (Cb) \[1\], and that if the 
Cb of an utterance is coreferentlai with the Cb of 
the prior utterance, it will be pronominallzed \[1\]. 
Kameyama \[6\] proposes that there are two means 
for retaining a discourse entity as the Cb, canon- 
ical center-retention--both references in subject 
role--and non-canonical center retention--neither 
reference in subject role. As shown in Fig. 1, 
the most enhanced context for lexical choice of it 
(context 1) was where both the pronoun and its 
pronominal antecedent were subjects, i.e., canoni- 
cal center-retention. The next most enhanced con- 
text for it (context 7) was where neither the pro- 
noun nor its pronominal antecedent were subjects, 
i.e., non-canonical center-retention. Thus, the def- 
inite pronoun correlates with both canonical and 
non-canonical center retention. 
Lexical choice of it is actively suppressed in 
contexts which are incompatible with center- 
retention. Note in Fig. 1 that if the antecedent is 
neither a pronoun nor a subject, a subsequent ref- 
erence via it in subject role is suppressed (contexts 
13 and 21). The only (non-rare) context where an 
it subject is neither enhanced nor suppressed is 
56 
where the antecedent is a canonical NP in subject 
role (context 9) (cf. §4.2). 
The demonstrative pronoun is actively sup- 
pressed in the case of canonical center-retention 
(context 2); i.e, given two successive pronominal 
references to the same entity where reference is 
maintained in subject role, the referent's atten- 
tional state is such that it precludes demonstrative 
reference. Use of that is also suppressed if the an- 
tecedent is a potential candidate for canonical cen- 
ter retention, even if reference is not maintained 
in subject role (context 4). 
Attentional state is only one component of a 
discourse structure. The discourse model as a 
whole will contain representations of many of the 
things to whcih the discourse participants can sub- 
sequently refer, including discourse entities evoked 
by NPs, and additionally, as argued by Webber 
\[18\], discourse segments. Webber notes that dis- 
course segment referents may have a different star 
tus from the discourse entities evoked by NPs, 
at least until they have been pronominally refer- 
enced. However, she suggests that when a demon- 
strative pronoun refers to a discourse entity, it 
accesses that entity by a process which first in- 
volves accessing the discourse segment in which 
the discourse entity is introduced. In other words, 
she posits two distinct referential processes, de- 
ictic and anaphoric reference, and suggests that 
even when a demonstrative pronoun refers to a 
discourse entity, the process of finding the refer- 
ent is distinct in kind from anaphoric reference 
to the same entity. While I have no evidence that 
bears directly on such a claim, my data do indicate 
that some entities in a discourse segment are ordi- 
narily unavailable via the demonstrative pronoun, 
namely entities that would be expected canonical 
centers, as described in the preceding paragraph. 
Thus my data support the view that there are dis- 
tinct processes for accessing entities in the model. 
It is relevant to note here that the notion of 
eb is generally discussed in terms of links between 
successive utterances. Since there is an extraor- 
dinary frequency of conjoined sentences in con- 
versational language, I distinguished between ut- 
terances and independent clauses within an ut- 
terance. The successive references in my data 
were in successive sentences a majority of the time 
(roughly 2/3; cf. \[13\]), but were sometimes sepa- 
rated by one or more sentences (roughly 1/6) and 
sometimes occurred in the same sentence (roughly 
1/6). This distance factor had no correlation with 
lexical choice of pronoun, which suggests that dis- 
course segment structure interacts with centering. 
The relevant local context for center-retention may 
not be successive sentences/utterances, but rather, 
successive sentences/utterances within the same 
discourse segment. In any case, for the data pre- 
sented here, the relevant local context consisted of 
two successive co-specifying phrases, not two suc- 
cessive utterances. 
Since the primary objective of this study was 
to examine various features of the context imme- 
diately preceding a given type of pronoun, rather 
than to track the discourse history of particular 
entities, little can be said here about the general 
case of multiple successive references to the same 
entity. However, I did investigate a subset of this 
general case, namely, successive pronominal refer- 
ences to the same entity where the initial men- 
tion was a canonical NP, and where each next co- 
specifying pronoun served as the antecedent for a 
subsequent pronoun. I refer to these as pronoun 
chains. 1° The relative likelihood of it and that 
was the same for the first slot in the chain, which 
conforms to the general distribution for pronouns 
with NP antecedents. The ratio of it to that in the 
last position of a chain conforms to chance, i.e., it 
equals the ratio of it to that in the pronoun chain 
sample. But within a chain, that is strongly pre- 
dicted by persistence of grammatical form. 
The demonstrative occured rarely within chains, 
but where it did occur, either the demonstrative 
token or its antecedent was a non-subject. This 
was found to he the only factor pertaining to lin- 
guistic structure that affected the occurrence of 
that within a pronoun chain. 
A final set of conclusions derived from the 
pronominal initial states in Fig. 1 pertains to the 
non-predictive contexts, i.e., those which neither 
enhance nor suppress center-retention, and those 
which neither enhance nor suppress demonstrative 
reference. These are cases where there is either 
a shift in grammatical role, or where the lexical 
choice is that (contexts 3, 5, 6 and 8). When a cen- 
ter is not retained across two successive utterances 
(in the same discourse segement), then it is likely 
that the global context is affected \[1\], perhaps by a 
center-shift (cf. \[5\]), or by a segment boundary (cf. 
\[7\], \[11\]). Centers seem generally to be unavailable 
for demonstrative reference, but contexts 6 and 8 
l°The term ~nm to have appeared in the philosophical 
and llngu~tic literature at about the same time, e.g., in 
worlm by K. Donnellan, C. Chastain, M. Halliday and D. 
Zubin. There were a total of 101 such chains comprising 
305 total pronoun toker~; they ranged in length from 2 to 
13 pronomm. 
57 
in Fig. 1 perhaps represent a mechanism whereby 
an entity maintained as center can become avail- 
able for demonstrative reference; e.g., context 6 
may coincide with the chaining context discussed 
in the preceding paragraph, whereby a locally fo- 
cussed entity can be accessed by that just in case 
the prior reference was a non-subject. Context 
8 suggests that demonstrative reference is more 
available in contexts of non-canonical center re- 
tention than canonical center retention. 
4.2 Non-Centered Discourse Enti- 
ties 
I have argued elsewhere that the crucial dis- 
tinction for the category of non-pronominal an- 
tecedents is the contrast between true NPS with 
NP syntax, versus all other types of syntactic argu- 
ments (\[12\] \[14\]). This raises two important issues 
pertaining to the status of the discourse entities 
evoked by Nl's versus other kinds of arguments. 
The first is that if non-NP arguments evoke dis- 
course entities, which they certainly must, such 
entities apparently have a different status in the 
model than discourse entities evoked by NPs, given 
that the combination of lexical choice between it 
and that and grammatical function so clearly dis- 
tinguish them. The second issue is that although 
the difference in status seems--at first blush--to 
correlate with a syntactic property, the distinction 
may ultimately be semantic in nature. I will dis- 
cuss each issue in turn. 
Two of the non-pronominal initial states in Fig. 
1 are distinguished by neither enhancing nor sup- 
pressing any of the possible transitions to it or 
that: NP subjects (9-12), and non-NV non-subjects 
(17-20). The extreme rarity of the latter suggests 
that non-NPs don't occur as grammatical subjects, 
or that when they do, they are not likely to be re- 
evoked by a pronoun. On the other hand, NP sub- 
jects are fairly frequent in the contexts where it 
or that occurs with a non-pronominal antecedent, 
thus the absence here of enhanced or suppressed 
transitions suggests that an entity mentioned as 
an NP subject is free to be accessed in a variety 
of ways, or more precisely, that it has a relatively 
unspecified attentional state. It is neither a par- 
ticularly likely Cb nor is it particularly available or 
unavailable for demonstrative reference. 
The two remaining non-subject initial states, 
i.e., NP non-subjects and non-NP non-subjects, 
both suppress subsequent reference via it subjects, 
as mentioned in the previous section. While NP 
subjects apparently have a somewhat unspecified 
attentional status, NP non-subjects enhance the 
lexical choice of non-subject that. It appears that 
discourse entities evoked by NPs which are not sub- 
jects are in an attentional state that is quite dif- 
ferent from that of canonical center retention. 
It is especially interesting that when the an- 
tecedent is a non-NP non-subject, a subsequent 
pronominal reference is most likely to be demon- 
strative, and most likely to be a subjectJ 1 The en- 
hancement of a that-subject context is completely 
contrary to the pattern established for subjects 
and for the demonstrative pronoun. These facts 
contribute to the view that entities evoked by non- 
NP constituents have'a special status, but what 
this status is remains to be determined. In pre- 
vious work, I emphasized the syntactic distinc- 
tion with respect to lexical choice between it and 
that \[14\]. Although the most obvious difference 
is the purely syntactic one, the syntactic distinc- 
tion between NP and non-NP constituents has a 
number of semantico-pragmatic consequences. In 
discussing the nominal and temporal anaphora 
within Kamp's framework of discourse represen- 
tation structures (DRS), Partee raised the ques- 
tion of the difference in status between event- 
describing clauses and nominalizations \[10\]. In- 
dependent clauses differ from the class of non- 
NP constituents under consideration here in that 
the latter occur as arguments of superordinate 
verbs, and are thus entities participating in a de- 
scribed situation, as well as descriptions of situa- 
tions. However, true noun phrases--whether they 
describe events or not--can have definite or indef- 
inite determiners, and cannot have tense or any 
aspectual categories associated with the verb. The 
study presented here brings us no closer to a so- 
lution to the questions posed by Partee regarding 
the ontology and representation of different kinds 
of event descriptions, but it does offer further con- 
firmation that entities evoked by NP and non-sP 
constituents have a different conceptual status, 
given the different possibilities for lexical choice 
and grammatical role of a subsequent pronominal 
mention. 
5 Conclusion 
The following bullets encapsulate the observations 
made in §4: 
11Cf. examples 3-6 in §2 for illustrations. 
58 
• Lexical choice of it indicates canonical or non- 
canonical center retention 
• Lexical choice of it in subject role conflicts 
with non-subject antecedents, but is compat- 
ible with an NP-subject antecedent 
• Lexical choice of that blocks canonical center 
retention 
• Lexical choice of that may be more compatible 
with non-canonical center retention 
• Lexical choice of that in subject role is most 
likely when the antecedent is a non-NP con- 
stituent 
• Lexical choice of that is enhanced when the 
antecedent is a non-NP constituent 
• Lexical choice of that is enhanced when the 
antecedent NP is a non-subject 
• NP subjects have a relatively unspecified at- 
tentional status 
ACKNOWLEDGEMENTS 
The data collection and statistical analysis were sup- 
ported by Sloan Foundation Grant 1-5680-22-4898. 
The computational analysis and preparation of the pa- 
per were supported by DARPA Contract N00014-85- 
C-0012. Many thanks to Elena Levy, Deborah Dahl, 
Megumi Kameyama, Carl Weir, Bonnie Webber and 
David Searls for helpful discussion, commentary and 
criticism. 

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