The Role Of Focussing in Interpretation of Pronouns 
Candace L. Sidner 
Artificial Intelligence Laboratory 
Massachusetts Institute of Technology 
Cambridge, MA 02139 
;rod 
Bolt, Beranek and Newman, Inc. 
50 Moulton Street 
Cambridge" MA 02138 
In this p;,per I \[ discuss the formal relationship between 
the process of focussing and interpret;ition of pronominal 
anaphora. The discussion of focussing extends the work of 
Grosz \[1977\]. Foct,ssing is defined algorithmical\]y as a process 
which chooses a focus of attention in a discourse and moves it 
around as the speaker's focus ch'mges. The paper shows how to 
use the focussing algorithm by ;m extended example given below. 
DI-I Alfred a,ld Zohar liked to play baseball. 
2 They played it everyday after school before 
dinner. 
3 After their game, the two usually went for ice 
cream cones. 
4 They tasted really good. 
5 Alfred always had the vanilla super scooper, 
6 while Zohar tried the flavor of the day cone. 
7 After the cones had been eaten, 
8 the boys went home to study. 
In this example, the discourse focusses initially on baseball. The 
focus moves in DI-3 to the ice cream cone. Using this example, 
I show how the formal algorithm computes focus and determines 
how the focus moves according to the signals which the speaker 
uses in discourse to indicate the movement. 
Given a process notion of focus, the paper reviews the 
difficulties with previous approaches (Rieger \[1974\], Charniak 
\[1972\], Winograd \[1971\], Hobbs \[1975\] and Lockman \[1978\]). 
Briefly, the first four authors all point out the need for 
inferencing as part of anaphora disambiguation, but each of 
their schemes for inferencing suffer from the need for control 
which will reduce the combinatorial search or which will insure 
only one search path is taken. In addition, Winograd and 
Lockman are aware of pronopn phenomena which cannot be 
treated strictly by inference, as shown below. 
D2-1 I haven't seen Jeff for several days. 
2 Carl thinks h e's studying for his exams. 
3 Oscar says hj is sick, 
4 but I think he went to the Cape with Linda. 
1. This report describes research done at the Artificial 
Intelligence Laboratory of the Massachusetts Institute of 
Technology. Support for the laboratory's artificial intelligence 
research is provided in part by the Advanced Research Projects 
Agency of the Department of Defense under the Office of 
Naval Research under Contract Number N00014-73-C4)643. 
However, their approaches are either simple heuristics which 
offer no unified treatment (Winograd) or require the 
computation of a structure which must assume the pronouns 
have previously been resolved (Lockman). 
In order to state formal rules for pronoun 
interpretation, the concept of antecedence is defined 
computationally as a relationship among elements represented in 
a database. Using this framework, the paper supports two 
claims by means of rules for antecedence. 
I. The focus provides a source of 
antecedence in rules for interpreting 
pronominal anaphora. 
2. Focussing provides a control for the 
inferencing necessary for some kinds of 
anaphora. 
The rules 
confirming 
restrictions 
The use of 
D3 below. 
D3-I 
2 
for pronominal anaphora rely on three sources of 
information: syntactic criteria, semantic selectional 
and consistency checks from inferencing procedures. 
these rules are presented for examples D2 above and 
Whitimore isn't such a good thief. 
The man whose watch he stole called the 
police. 
3 They catzght him. 
These examples show how to use the three sources of 
information to support or reject a predicted antecedence. In 
particular, inferencing is controlled by checking for consistency 
on a predicted choice rather than by search ~lsing general 
inference. 
The paper also indicates what additional requirements 
are needed for a full treatment of pronominal anphora. These 
include use of a representation such as that of Webber \[197g\]; 
linguistic rules such as the disjoint reference rules of Lasnik 
\[\[976\] and Reinhart \[\[976\] as well as rules of anapbora in 
logical form given by Cbomsky \[1976\]; and presence of actor 
loci such as they in D3. The nature of these requirements is 
discussed, while the computational inclusion of them is found in 
$idner \[ 1979\]. 
"77 
1. References 
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Comprehension. M.I.T.A.I. Lab TR-266. 
Chmnsky, N. \[1976\] Conditions on Rules o\[ Grammar. Linguistic 
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78 
