Signalling the Interpretation of Indirect Speech Acts 
Philip R. Cohen 
Center for the Study of Reading 
University of Illinois, & 
Bolt, Beranek and Newman, Inc. 
Cambridge, Mass. 
This panel was asked to consider how various "problem 
contexts" (e.g., cooperatively assembling a pump, or 
Socratically teaching law) influence the use of language. 
As a starting point, I shall regard the problem context 
as establishing a set of expectations and assumptions 
about the shared beliefs, goals, and social roles of 
those participants. Just how people negotiate that they 
are in a given problem context and what they know about 
those contexts are interesting questions, but not ones I 
shall address here. Rather, I shall outline a theory of 
language use that is sensitive ¢o those beliefs, goals, 
and expectations. 
The theory is being applied to characterize actual 
dialogues occurring in the Familiar task-orlented slt- 
uation ~O.1, in which an expert instructs a novice Co do 
something, in our case to assemble a toy water pump. In 
such circumstances, the dialogue participants can be 
viewed as performing speech acts planned, prlmarl\]y, to 
achieve goals set by the task. Other contexts undoubted- 
ly emphasize the instrumental uses of language (e.g.,~) 
but those problem contexts will not be considered here. 
The application of a model of speech act use to actual 
dialogue stresses the need For sources of evidence to 
substantiate predictions. The purpose of this paper is 
to point to one such source -- speaker-reference ~9\]- 
The natural candidate for a theory of instrumental use 
of speech acts is an account of rational action ~ -- 
what is typically termed "planning". However, contrary 
to the assumption of most planning systems, we are in- 
terested in the planning of (usually) cooperative agents 
who attempt to recognize and facilitate the plans of 
their partners ~,h,5,\]6,20\]. Such helpful behavior is 
independent of the use of language, but is the source of 
much conversational coherence. 
A plan based theory of speech acts specifies that plan 
recognition is the basis for inferring the illocuCionary 
force(s) of an utterance. The goal of such a theory is 
to formalize the set of possible plans underlying the use 
of particular speech acts Co achieve a given set of goals. 
In light of the independent motivation for plan generation 
and recognition, such a Formalism should treat commun- 
icative and non-communlcatlve acts uniformly, by stating 
the communicative nature of an illocutlonary act as part 
of chat act's definition. A reasoning system, be it 
human or computer, would then not have to employ special 
knowledge about communicative acts; it would simply at- 
tempt Co achieve or recognize goals. 
The components of speech act p\]annlng and recognition 
systems developed so far include: a Formal language for 
describing mental states and states of the physical and 
social worlds, operators for describing changes of state, 
associations of utterance features (e.g., mood) with cer- 
taln operators, and a set of plan construction and re- 
cognition inferences. Illocutionar'y acts are defined as 
operators that primarily affect the mental states of 
speakers and hearers L3,8,13,I7J. 
To be more specific, in the most fully developed at- 
tempt at such a theory, Perraulc and Allen ~ show how 
plan recognition can "reason out" a class of indirect 
speech acts. Briefly, they define "surface =' speech act 
operators, which depend on an utterance's mood, and op- 
erators For illocutionary acts such as requesting. Plan 
recognition involves inferences of the form "the agent 
intended to perform action X because he intended to ach- 
ieve its effect in order to enable him to do some other 
action Y". Such inferences are applied to surface speech 
act operators (characterizing, for instance, "Is the salt 
near you?") to yield iilocutionary operators such as 
* For this brief paper, I shall have Co curtail discussion 
of the planning/plan recognition literature. 
requests to pass the salt. 
The remainder of this paper attempts to illustrate the 
kinds of predictlons made by the theory,.and the use of 
anaphora to support one such prediction." Consider the 
following dialogue fragment (transmitted over teletype) 
in the water pump context described earlier: 
Expert: l). '~e need a clear bent tube For the bottom 
hole." 
Novice: 2). "OK, it's done." 
Expert: 3). "OK, now, start pumping" 
The example is constructed to illustrate my point, but it 
does not "feel" artificial. Experiments we are conducting 
show analogous phenomena in telephone and teletype modes. 
The theory predicts two inference paths For utterance 
I -- "helpful" and "intended". In the Former case, the 
novice observes the surface-lnform speech act indicated 
by a declarative utterance, and interprets it simply as 
an inform act that communicates a joint need. Then, be- 
cause the novice is helpful, she continues to recognize 
the plan behind the expert's utterance and attempts to 
further it by performing the action of putting the spout 
over the hole. The novice, therefore, is acting on her 
own, evaluating the reasonableness of the plan inferred 
for the expert using private beliefs about the expert's 
beliefs and intentions. Alternatively, she could infer 
that the expert intended for it to be mutually believed 
that he intended her to put on the tube. Thus, the novice 
would be acting because she thinks the expert intended 
for her ¢o do so. Later, she could summarize the expert's 
utterance and intentions as a request ~7\]. Perrault and 
Alien supply heuristics that would predlct-~" the preferred 
inference route to be the "intended" path since it is 
mutually believed that putting the tube on is the relev- 
ant act, and his intending that she perform pump-related 
acts is an expected goal in this problem context. To use 
Perrault and Alien's model For analyzing conversation, 
such predictions must be validated against evidence of 
the novice's interpretation of the expert's intent. 
Signalling Interpretation of Intent 
For this problem context and communication modality, 
the novice and expert shared knowledge that the exoert 
will attempt to get the novice to achieve each subgoal 
of the physical task, and the novice must indicate suc- 
cessful completion of those subtasks. However, not all 
communicative acts achieving the goal of indicating suc- 
cessful completion provide evidence of the novice's in- 
terpretation of intent. For instance, the novlce might 
say "I've put the bent tube on" simply to keep the expert 
informed of the situatlon. Such an informative act could 
arise if the problem context and prior conversation dld 
not make the salience of putting the tube on mutually 
known. To supply evidence of the novice's interpretation 
of intent, her response must pragmatically presuppose 
that interpretation. 
In our example, the novice has used "it" to refer to 
the action she has performed. It has been proposed that 
definite and pronomlnal/pro-verbal reference requires 
mutual belief chat the object in question_ --is in Focus 
O0,,s\] and satisfies the "descript,on'l t6,l  . Assuming 
that the,_inferring of mutually believed goals places them 
in focusU~ , the shared knowledge needed to refer using 
"it" is supplied by only one of the above interpretations 
-- the one summarizable as an indirect request. 
Robinson ~!~ has identified this problem of reference 
to actions and has implemented a system to resolve them. 
In chls paper, I stress the importance of that work to 
theories of speech act use. 
29 
Other signals of the interpretation of intent need to 
be identified to explain how the expertis "OK, now start 
pumping" communicates that he thinks she has inter- 
preted him correctly -- mutual signalling of intent 
and its interpretation is central to conversational 
Success. 
A formal theory that could capture the belief, in- 
tention, and focus conditions for speaker-reference is 
thus clearly needed to validate models of speech act use. 
A plan-based theory might accomodate such an analysis via 
a decomposition of currently primitive surface speech 
acts to include reference acts \[2,18J. By planning ref- 
erence acts to facilitate the hearers' plans (of. ~43), 
a system could perhaps also answer questions coopera- 
tively without resorting to Gricean maxims or "room 
theories" \[19.~. 
I have given a bare bones outline of how a descrip- 
tion of speaker-reference can ser~e as a source of em- 
pirical support to a theory of speech acts. However, 
much more research must take place to flesh out the 
theoretical connections. I have also deliberately av- 
oided problems of computation here, but hope the panel 
will discuss these issues, especially the utility of 
computational mode is to ethnographers of conversation. 
Acknowledgements: 
I would llke to thank Chip Bruce, Scott Fertig, and 
Sharon 0vlatt for comments on an earlier draft. 
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