TEMPORAL REASONING IN NATURAL LANGUAGE UNDERSTANDING: 
THE TEMPORAL STRUCTURE OF THE NARRATIVE 
Alexander Nakhimovsky 
Department of Computer Science 
Colgate University 
Hamilton, NY 13346 USA 
CSNet: sasha@colgate 
Abstract 
This paper proposes a new framework for dis- 
course analysis, in the spirit of Grosz and Sid- 
ner (1986), Webber (1987a,b) but differentiated 
with respect to the type or genre of discourse. It 
is argued that different genres call for different 
representations and processing strategies; par- 
ticularly important is the distinction between 
subjective, pefformative discourse and objective 
discourse, of which narrative is a primary ex- 
ample. This paper concentrates on narratives 
and introduces the notions of temporal focus 
(proposed also in Webber (1987b)) and narra- 
tive move. The processing tasks involved in re- 
constructing the temporal structure of a narra- 
tive (Webber's e/e structure) are formulated in 
terms of these two notions. The remainder of 
the paper analyzes the durational and aspectual 
knowledge needed for those tasks. Distinctions 
are established between grammatical aspect, as- 
pectual class and the aspectual perspective of a 
sentence in discourse; it is shown that in En- 
glish, grammatical aspect under-determines the 
aspectual perspective. 
NARRATIVES 
This paper investigates the varieties of tempo- 
ral knowledge and temporal reasoning that are 
at work in understanding extended narratives. 
It starts out by developing a new framework for 
narrative representation, a framework that has 
developed independently from, but is very sim- 
ilar to Webber, 1987a, 1987b. It also builds on 
the ideas of Grosz and Sidner (1986), but refor- 
mulates them specifically for the task of narra- 
tive understanding. A reformulation, I believe, 
is needed because different genres of discourse - 
narrative, expository text, task-oriented dialog, 
argument, etc. - have different principles of or- 
ganization that call for different representations 
and processing strategies. Without offering a 
comprehensive taxonomy of discourse genres I 
would llke to stress that narrative stands out 
by virtue of its two properties: it is objective 
and it unfolds in time. 
A distinction between subjective and objec- 
tive modes of discourse has been drawn by many 
authors in linguistics and structuralist poetics, 
who all "have a category of narration to which 
another category is opposed; and they all agree 
that the non-narrative category is more subjec- 
tive ~ (Lyone,1982:117). One manifestation of 
the objectivity of narratives is the structure of 
the underlying intentions. This structure plays 
an important role in Grosz and Sidner, 1986 
who propose, inter alia, are that (a) the con- 
tent of discourse is embedded in, and classified 
by, the speaker's intentions which form a hier- 
archical intentional structure, and (b) the con- 
tent structure is separate from the attentional 
state, and both are rather indirectly represented 
by the linguistic material of discourse, orga- 
nized in a hierarchical structure of discourse 
segments. I adopt (b) without reservations, 
but (a), I suggest, needs to be modified and 
differentiated. In dialogs the structure of in- 
tentions is, indeed, rich and informative (note 
that most indirect speech acts occur in dialogs); 
in narratives and expository prose the inten- 
tion is practically constant: aintend that the 
other discourse participant believe proposition 
p~ (cf. Grosz and Sidner, 1986:184). In other 
words, the only discourse purpose of a narra- 
tive or its segments is to modify the memory 
of the other discourse participant. Removing 
this, rather uninformative, top level of inten- 
tion, reveals the %bjective ~ content structure 
of the narrative, whose main building block ls 
a situation persisting or evolving in time, best 
visualized as a four-dimensional piece of time- 
space. Loosely following Hayes, 1978 I use the 
term history-token (h-token) for all varieties of 
such situations (events, processes, activities, ha- 
262 
bitual actions, etc); each h-token is an instance 
of a hiztory-type (h-type) corresponding to ab- 
stract situations types of Situation Semantics. 
I assume that associated with each predicate of 
the meaning representation language is a set of 
roles such as Agent, Object or Patient; an h- 
type is a predicate together with its roles and a 
selectional restriction on them (cf. Creary and 
PoUard, 1985, Hobbs etal, 1986). 
Removing the top layer of intentions leads 
to other changes in the Grosz-Sidner model. 
Each discourse segment (DS) is now character- 
ized by its main h-token, rather than its DS pur- 
pose. An h-token is, in turn, characterized by 
a spatio-temporal location, a set of participants 
and a time scale. Dominance relations between 
intentions correspond to compositional relations 
between h-tokens: the h-token of entering a 
room decomposes into opening the door, cross- 
ing the threshold, closing the door (provided 
there is a door to open and close). Satisfaction- 
precedence relations between intentions corre- 
spond to the temporal and causal relations be- 
tween histories. Thus re-interpreted, the pair 
intentional structure-attentional state of Gross 
and Sidner, 1986 becomes very similar to Web- 
her's (1987a:137) proposal: aAlong with build- 
ing up a discourse model of the entitles salient 
to the given text, the listener is also building 
up a model of the events and situatons they 
participate in-e/s structure. = (Although Web- 
her speaks of a Itext' in general, I believe she 
means 'a narrative text,' and all her examples 
are such.) To emphasize the similarity of the 
two approaches, and to avoid proliferation of 
terminology, I use Webber's term e/s structure 
for the representation of the narrative's con- 
tent, but retain Gross and Sidner's terminology 
for the attentional state and speak of a focus 
space (FS) corresponding to each DS, and a fo- 
cus space stack (FS stack). An important dif- 
ference is that I don't think anything ever gets 
popped of the FS stack: it just keeps growing, 
representing the linear progression of the text 
(while the e/s structure represents the tempo- 
ral progression of its content). It is a stack 
only in the sense that its top element is the 
easiest to access, not in the sense of following 
the LIFO discipline. Even interruptions, di- 
gressions and flashbacks, to which the pop-off 
action seems most applicable, are better repre- 
sented as a move into a new FS, accompanied by 
a promise to return: to return to the immedi- 
ately preceding FS in the case of interruptions, 
and to a specified position in the e/s structure 
in the case of digressions and flashbacks. 
The constancy of intention is one aspect of 
the narmtive's objectivity; another one is its 
"closeness unto itself" in the processing of defi- 
nite and temporal anaphora. Subjectivity goes 
with deixis, the constant presence of the situa- 
tion of utterance in the processing model. Ob- 
jective texts' contents are removed from deixis 
into a separate universe, which, in the case of 
narratives, is endowed with its own, separate 
timeline. In some languages this separateness is 
clearly signalled by special narrative-beginning 
devices and/or narrative tenses (Dahl, 1985). In 
English, there is of course an overlap between 
the "narrative = and "non-narrative = tenses, but 
it is far less complete than is usually supposed: 
one could go through a book on computer sci- 
ence and not find a single occurrence of a past 
tense, except, perhaps, in short passages on the 
history of particular ideas; conversely, one could 
go through a long novel and not find a single 
sentence in the present or future, except in the 
characters' dialogs. 
Behind the superficial dl~erence in the use 
of tenses stands the more important one in the 
basic meaning of the grammatical category of 
tense. The standard view is that tense in- 
dicates relative position in time with respect 
to the speech event (Comrie, 1985). In di- 
alogs tense indeed appears in its deictic func- 
tion, which is also the dominant function of the 
present and future tenses. However, past tenses 
are diferent, especially in narratives; consider: 
~On March 5, 3275, Captain Kirk got up early, 
shaved and boarded the Enterprise. ~ Surely, 
the form of the verb 8base does not mean that 
the Captain was clean-shaven before the book 
went to print. Rather, it indicates that we are in 
a narrative, and it helps position the event vis- 
a-vis the narmtive's preceding events. In other 
words, narrative tenses are anaphoric, not delc- 
tic. An analogy with pronouns is, perhaps, use- 
ful: although 3 person pronouns are grouped to- 
gether with I and you in traditional grammars, 
and although they can be used deicticaUy (if 
strongly accented and accompanied by a ges- 
ture) their primary function is anaphoric. 
The anaphorlc nature of past tenses (first rec- 
ognized in Partee (1973), investlg~ted specifi- 
cally in narratives in Hinrichs (1986)) has im- 
portant computational implications, for anaphora 
can only be resolved with respect to a con- 
stantly maintained and updated focus (Gross, 
1977; Sidner, 1983). To emphasize the par- 
aUel between temporal and definite anaphora, 
I will speak of the temporal focus of a narra- 
tive. (The same term for the same concept and 
263 
with the same motivation is proposed in Web- 
her, 1987b; in Nakhimovsky 1986, 1987 I speak 
of the Active Window on discourse, or Window 
for short; I~mp and Rohrer, 1983 have recy- 
cled Reichenbach's Reference Point for a sim- 
ihr concept.) If the focus eimpliciter answers 
the question =What are we talking about? u the 
tempor~ focus answers the question ZWhere in 
time IS the narrative now? w As the narrative 
progresses, the temporal focus changes its po- 
sition in time; I will refer to the movement of 
temporal focus from one sentence of the narr'~- 
tive to the next as t/~e na~ative move. 
A narrative move can remain within the cur- 
rent FS, or shift to a different one, which can 
be totally new or a resumption of a~u old FS 
from the stack. (In terms of linguistic structure, 
the current sentence may continue the same, or 
start a new, DS.) The two kinds of narrative 
moves will be called micro- and macro-moves, 
respectively. Examples (1)-(3) contrast the two 
kinds of moves and Illustrate other concepts in- 
troduced in this section. 
(1) a. John entered the president's once. b. 
The president got up. 
This is narrative at its simplest: an orderly 
progression of events within the same narrative 
unit. The required Inferential work le relatively 
transparent. The event of John's entering the 
once results in the state of his being in the of- 
rice: this le part of the lexical meaning of enter. 
The temporal focus is inside this state, at its 
beginning. Sentence b., which in \]sol=tion could 
mean that the president got up from his bed at 
home, is interpreted vis-a-vis the position of the 
temporal focus: the president was in his office, 
sitting; he saw John and got up; both men are 
now standing, 'now' referring to the temporal 
focus as it always does. This example shows 
that it would be more accurate to speak of the 
spatio-temporal focus to which the current situ- 
ation is anchored (cf. Barwiee and Perry, 1983) 
but I leave the spatial dimensions of narrative 
for future research. 
Examples (2) and (3) Illnstmte macro-moves: 
(2) a. Gradually, H~rvey ber~n to yield the 
details of his crime, prodded by the persistent 
questions of the investigator, b. He arrived at 
the bank at 4 p.m. dressed as a postal worker. 
(3) a. Hartley and Phoebe had been sent by 
their mother to fix the tail v-~hve of the windmilL 
b. In the great expanse of the prairie where 
they lived, the high tower of the windmill was 
the only real landmark (Worline, 1956:1). 
In (2), the similarity between definite and 
temporal anaphora stands out quite clearly. 
Just as he in sentence b. anaphoricaily evokes 
discourse-prominent \]~rvey, so arrived evokes 
the time of the discourse-promlnent crime event 
and ~ p.m. evokes the day of that event. Just as 
he selects for anaphoric reference one of two dis- 
course entities available for pronominalization, 
so art/red and ~ p.m. select one of two available 
events, the interro~-~tion and the crime. The 
shift of temporal focus to an earlier event, over 
a considerable time interval, signals the begin- 
ning of a new DS. The FS associated with the 
old DS is saved on the stack together with the 
last position of the temporal focus in it, which is 
under-determined by the English narmrive: it 
can be within, or right after, the reconstructed 
the details history. If the DS is resumed with 
Harvey took a sip of water ~nd mopped Aie brow, 
we don't know whether the reconstruction is 
over or not. 
In (3) the beginning of a new DS in sentence 
b. is indicated by a drastic change in time scMe, 
rather than movement of focus. Sentence a. 
establishes, either directly or through simple, 
lexicon-ba4~ed inferences, three events: the tail 
v~ne broke, mother sent the children to fix it, 
the children set off walking. The temporal fo- 
cus, Indicated by the past perfect tense, is in the 
middle of the wallri~g event; the time scale of 
the entire sequence is within a day or two. The 
time scale of sentence b, Indicated by the ~uAere 
thev lived chuee a~d the lifetime of a windmill 
(h~cDermott, 1982), is years or decades. (Note 
the accompa~ylng shift in the spatial scale from 
one household to the entire prairie.) 
Narrativse (1)-(3) |11narrate several impor- 
tant points about the temporal focus. First, 
it is always Inside some history, either directly 
narrated or inferred. If that history has a built- 
in terminM point that is reached in the normal 
course of events, the position of the focus sets 
up the expectation that, within a certain time 
scale, the terminal point will be reached. So, 
in (3) we expect the children to make it to the 
windmill before it gets dark, and indeed, after a 
page of background material, the FS of (3a) is 
resumed, with children already standing at their 
destination. Second, the position of the tempo- 
ral focus may be under-determined, as in (2), 
but there are precisely two possibilities: inside 
or right after the most recently narrated his- 
tory. Adopting the terminology of Smith (1986) 
I will speak of the imperfective and perfective 
sentence perspective, respectively. 
Given the conceptual apparatus that has 
264 
been developed in this section, several tasks in- 
volved in narrative understanding can be spec- 
ified. The tasks are clearly interrelated, but in 
this paper I make no comment on how the in- 
teraction can be set up. 
(4) As each new sentence of the narrative 
comes in do: 
• a. determine the type of narrative move 
(micro or raaero) that the new sentence 
represents. If it is a macro-move, update 
the FS stack and position the new F5 in 
the ezisting e-s structure. If it is a micro- 
move, determine the temporal relations be- 
tween the histories described by the current 
and the preceding sentence. 
• b. using knowledge about durations and as- 
pectual classes of events, determine the as- 
pectual perspective of the new sentence and 
the position of the temporal focus; 
• e. using knowledge about causality and in- 
ternal constituency of events, add inferred 
events to the narrated ones; update old ez- 
pectations and set up new ones. 
Several kinds of temporal knowledge are thus 
brought to bear on the process of narrative un- 
derstanding. First, there is knowledge about 
durations and time scales, and the interaction, 
totally disregarded in existing work, between 
the event structure of the narrative and the hi- 
erarchy of ~received n time cycles such as times 
of day, seasons of the year and the stages of hu- 
man life. Second, there is compositional knowl- 
edge about internal constituency of events and 
their terminal points. Third, there is aspectual 
knowledge, both lexical, about intrinsic prop- 
erties of histories, and grammatical, about the 
way the history is presented by a given verb 
form. The remainder of this paper investigates 
these three kinds of knowledge and the ways 
they are represented in the lexicon and utilized 
in narrative understanding. 
DURATION 
Information about durations can be entered in 
the lexicon in the following three ways that 
are not mutually exclusive: (a) most generally, 
as qualitative functional dependencies (Forbus, 
1985) among the participants of the situation; 
so, the time it takes to read a text depends 
on its length and genre, and the proficiency of 
the reader;, (b) for some h-types (e.g. lecture, 
shower, lunch) the duration of their h-tokens is 
stable and can be entered in the lexicon directly 
as a fuzzy number (e.g. lecture \[1,2 hour\]; (c) for 
a majority of h-types, the tlme scale of their h- 
tokens is quite narrowly constrained, where the 
time scale of an interval is a sequence of mea- 
surement units that are anaturaln to it: mea- 
sured in a natural unit, the length of the in- 
terval will not be a very small fraction (greater 
than some constant R) or a very big number 
(less than some constant N). The important 
ideas are, first, that measurement units form 
a small set that is partially civilization specific, 
partially determined by the biological and phys- 
ical universals; second, that the duration of an 
h-token constrains the choice of measurement 
units in which its duration is measured and thus 
the precision of measurements: when we say It 
took loan an hour to repair a faucet we don't 
mean that it took him 3600 seconds. 
An important durational class of h-tokens 
is instantaneous events. There is a persistent 
misconception, inspired by scientific thinking, 
that the notion of an instantaneous or punc- 
tual event can only be defined relative to a time 
scale because awe can always 'increase the mag- 
nification' and find more structure s (Allen and 
Kauts, 1985:253; see also Dowry, 1986, Kamp, 
1979). I believe that instantaneousness is an 
absolute quality determined by our biology: in- 
stantaneous events are those that are not per- 
ceived by humans as possessing internal struc- 
ture. Languages select such events for special 
treatment by disallowing the ~imperfectlve de- 
scription B of them: one cannot use the imper- 
fective aspect to place the temporal focus in the 
middle of an instantaneous event, so that The 
light was flashing does not place the temporal 
focus inside an individual flash. (More on as- 
pects below.) 
Non-lnstantaneous events are, intuitively, 
discrete and countable entities with a distinct 
beginning and end; packaged in between the 
beginning and end of an event is the %tuif 
the event is made of, = which is a process or 
state. This intuitlon is dlscussed in a consider- 
able body of literature that compares the event- 
process and count-mass oppositions (Moure- 
latos, 1981, Bunt, 1985, Bach, 1986). As I ar- 
gue in Nakhimovsky (1986), all these authors 
should also have allowed for events made out of 
states, as, for example, the event described by 
Bobby took a nap. Surprisingly, collocations of 
this nature have never, to my knowledge, been 
discussed in connection with the English aspec- 
tual system. (Cf. also did some reading, went 
265 
/or a v~at~ ) 
The distinctions event-process and process- 
state are thus orthogonal to each other, rather 
than forming a single classification as in Moure- 
latos, 1981; Allen, 1984. The former distinction 
is one of aspect: %he term 'process' means a dy- 
namic situation viewed imperfectively, and the 
term 'event' means a dynamic situation viewed 
perfectively m (Comrie, 1976:51). The latter dis- 
tinction is one of aspectual class. This is elabo- 
rated in the next section. 
ASPECT 
In what follows it is essential to keep the follow- 
ing three concepts apart: aspect as a grammati- 
cal category of the verb, implemented by affixes, 
auxillarles and such; aspectual class, which is 
a characteristics of an h-type or lexical mean- 
ing; the aspectual perspective of the sentence. 
Both grammatical aspect and aspectual class 
sometimes uniquely determine, sometimes just 
strongly constrain, the aspectual perspective. 
In English, the progressive aspect guarantees 
that the sentence perspective is imperfective; 
in any language, instantaneous events are pre- 
sented perfectively (which does not mean that 
the corresponding verbs are in any sense per- 
fective). All three concepts are needed for un- 
derstanding the workings of aspectual systems; 
I don't think anybody in the abundant recent 
literature on aspect keeps all three clearly apart. 
There are languages, most notably Slavic, 
where the difference in the sentence perspective 
is hard-wired into verb morphology: simplify- 
ing slightly, every Russian verb is either perfec- 
rive or imperfective, and the morphological fea- 
ture of the verb determines the aspectual per- 
spective of the sentence. (In fact, the English 
term 'aspect' is a mistranslation of the Russian 
term 'rid,' 'view, perspective.') In other words, 
I claim, rather audaciously, that grammatical 
aspect is a purely attentional device that helps 
determine the position of the temporal focus; 
all the other shades of aspectual meaning re- 
sult from interactions between this (pragmat- 
ically defined) Grundbsdeutung and numerous 
other factors, including aspectual class, dis- 
course genre, and general pragmatic principles 
of language. 
The following examples, adopted from Dowty 
(1986), illustrate the interplay between aspect, 
aspectual class and the micro-move of the nar- 
rative. (I repeat (1) here for convenience.) 
(1) a. John entered the president's office, b. 
The president got up. 
(5) a. John entered the president's office, b. 
The president was asleep, c. The clock on the 
wall ticked loudly. 
(6) a. John entered the president's office, b. 
The president was writing a letter. 
Sentences (la) and (lb) describe two pro- 
cesses (entering and getting up) that each have 
a built-in terminal point that is reached in 
the normal course of events and beyond which 
the processes cannot continue. (In Vendler's 
(1967) well-known classification such processes 
are called accomplishments; I call them, follow- 
ing Comrie (1976), tellc processes.) The aspec- 
tual perspective of both sentences is peffective; 
the events of the two sentences are understood 
to have happened in succession; the temporal 
focus has advanced to the time when both men 
are standing. 
Sentences b. and c. in (5) describe a state 
and an atelic process, respectively. They are 
understood to have begun before the event of 
sentence 1, and to persist in parallel The tem- 
poral focus stands still. Note that the sentence 
perspective of b. and c. is determined by the 
aspectual class, not grammatical aspect. In (6), 
however, the sentence perspective of b., and the 
micro-move from a. to b., are determined by the 
progressive form of the verb: alt.hough writing 
a letter is a relic process the mlcro-move in (6) 
is the same as in (5). 
The history of misconceptions concerning the 
English aspectual system can be summarized 
as follows. First it was believed that English 
has no aspect; progresslve was called a tense. 
When it came to be recognized that progres- 
sive is a variety of the impeffectlve aspect, the 
next misconception was to assume that since 
English has an hnpeffectlve, it ought to have 
a peffective also, with simple past an obvious 
candidate. However, examples like (5c) show 
that a sentence with a verb in simple past can 
have the imperfective perspective. The cur- 
rent consensus seems to be that simple past 
of accomplishment verbs is peffective (Hinrichs, 
1986:68; Dowty, 1986:46-8). In other words, if 
the verb form = simple past and the aspectual 
class = telic process then the sentence perspec- 
tive is peffective and the temporal focus ad- 
vances. Consider, however, example (7), where 
two accomplishments, both described by verbs 
in the simple past, unfold in parallel and are 
both interrupted by a doorbell: 
266 
-" ? 
(7) a. After supper, Alice and Sharon sat 
down in the living room. b. Alice read a book, 
Sharon watched her favorite ballet on television. 
c. Suddenly the doorbell rang. 
Other examples of micro-moves that violate 
Hinrichs' rule are given in (8) and (9), quoted 
from Dowty, 1986. (The rule can also be vio- 
lated by a macro-move, as in example (2)). 
(8) John knelt at the edge of the stream and 
washed his hands and face. He washed slowly, 
feeling the welcome sensation of the icy water 
on his parched skin. (From Dry, 1983) 
(9) Pedro dined at Madam Gilbert's. First 
he gorged himself on hors d'oeuvres. Then he 
paid tribute to the fish. After that the butler 
brought in a glazed chicken. The repast ended 
with a flaming dessert. (From Kamp, ms.) 
I conclude that English has no (morphologi- 
cal) peffective; it has a marked impeffective and 
an unmarked default that does not provide sub- 
stantial information about the aspectual per- 
spective of the sentence (cf. Dahl, 1985 for 
the same view). In other words, English mor- 
phology, even combined with aspectual class, 
underdetermines the sentence perspective and 
the mlcro-move of the narrative. However, the 
number of possibilities is limitied, and an ex- 
tensive empirical investigation could, I believe, 
produce a full catalog of micro-moves commonly 
employed in Western narratives. 
ASPECTUAL CLASS 
The major division among non-instantaneous 
histories, recognized at least since Aristotle, 
is between process (energela) and state (sta- 
sis). In recent times, Vendler (1967) proposed a 
highly influential classification that is still com- 
monly accepted, although the principles of clas- 
sification have changed. Vendler believed, erro- 
neously, that he was classifying English verbs, 
rather than sentence denotations, and he used 
such language-specific criteria as whether or not 
a verb has a progressive form (Vendler's sta- 
tives, such as know, don't). In the model- 
theoretical version of Taylor and Dowry, the 
classification is based on the relationship be- 
tween the truth value of a sentence at an in- 
terval and at its subintervals; so, for instance, a 
sentence S is stative (denotes a state) iff it fol- 
lows from the truth of S at an interval I that S 
is true at all subintervals of I. (Dowty, 1986:42). 
I submit that these criteria cannot possibly 
be right, i.e. capture the real distinctions oper- 
ative in the workings of human language: these 
have to relate to something perceived and expe- 
rienced, rather than truth values (which is not 
to deny that real distinctions may result in fairly 
consistent truth-functional properties). It is not 
accidental that Dowty's own example of a state 
(sleep) contradicts his definition: we can truth- 
fully say that Bob slept from 10 to 6 even if he 
got up once to go to the bathroom. My proposal 
is that we take the physical vocabulary of pro- 
cesses and states seriously, and classify historles 
according to their internal dynamics, the stabil- 
ity of their parameters and the resources they 
consume. (Part of the internal dynamics, in the 
presence of a conscious agent, is the degree of 
volitional controL) We can then note the dis- 
tinction between states that do not require any 
resources to sustain themselves (know English, 
own a house) and those that do (sleep requires 
a certain amount of sleepiness that gradually 
wears out). The sub-interval property holds 
only for zero-resource, zero-control states, and 
is, in fact, a simple consequence of their other 
properties: a state that requires no resources 
and cannot be dropped in and out of at will 
obtains continuously. 
Resource-consuming states all seem to re- 
quire only generic internal resources, which 
are not specific to any given state but rather 
to all individuals of a given sort. Within 
processes, there are those that require only 
generic resources (walking) and those that re- 
quire process-specific resources as well: read- 
ing, for example, requires not only being awake 
and not too hungry, but also a text to read. 
Telic processes can be defined as processes that 
consume a specific amount of a domain-specific 
resource. Resources are understood broadly: 
walking from A to B consumes the distance be- 
tween them, building a house consumes the as- 
yet-unbuilt but envisioned part of it, and de- 
stroying a house consumes the finite amount 
of %tructure = or %rder ~ built into it. These 
examples illustrate three main classes of relic 
processes: creating an object, destroying an ob- 
ject, and moving a specified amount of material 
(possibly the mover himself) to a specified des- 
tination. A subclass of destruction processes 
are ingestions, which convert an external re- 
source into an internal one. Moving is under- 
stood to include all three of Schank's PTRANS, 
ATRANS and MTRANS classes, with the pro- 
viso that, unlike physical motion, MTRANS re- 
ally copies structures from the source to the des- 
tination. Moving also includes gradual (but not 
267 
instantaneous) changes of state. 
Lacking internal structure, instantaneous events 
have to be classified by comparing the world be- 
fore and after them. An instantaneous event 
can terminate either a process or a state, and 
it can initiate either a process or a state; if it 
is sandwiched in between two processes or two 
states, the two can be the same or different. 
The resulting classification, discussed in Nakhi- 
movsky, 1987, captures linguistically significant 
distinctions: for instance, most English verbs 
describing instantaneous events fall into those 
groups where the instantaneous event meets a 
state. 
FUTURE RESEARCH 
Perhaps the biggest task involved in narra- 
tive understanding is to infer, using knowl- 
edge about causality and the internal con- 
stituency of events, the missing links between 
narrated events and the temporal relations be- 
tween them. This involves solving qualitative 
functional equations that hold between the pa- 
rameters of described histories and resources 
they consume (cf. Forbus, 1985), and prop- 
agating durational constraints (of. Allen and 
Kautz, 1985). An analysis of the required lex- 
ical knowledge is presented in this paper and 
Nakhlmovsky (1987). The subject is further de- 
veloped in Nakhimovsky (in preparation). 
ACKNOWLEDGEMENTS 
I'm grateful to Colgate University for giving 
me a leave to do research, and to Yale's AI 
Project for providing a stimulating environment 
for it. My conversations with Tom Myers, 
Donka Farkas and Larry Horn have helped me 
clarify my ideas. Alex Kass read a draft of the 
paper and provided valuable comments and in- 
valuable technical assistance. 
REFERENCES 
Allen, James, and Kautz, H. A. 1985. A model 
of naive temporal reasoning. In Hobbs and 
Moore, 1985. 
Bach, Emmon. 1986. The algebra of events. 
Linguistles and Philosophy, 9:5-16. 
Bobrow, Daniel. (Ed.) 1985. Qualitative 
Reasoning about Physleal Systems. Cambridge, 
~Lk: MIT Press. 
Bunt, H. 1985. The formal representation 
of (quasi) continuous concepts. In Hobbs and 
Moore, 1985. 
Comrie, B. 1976. Aspect. Cambridge: Cam- 
bridge University Press. 
Comrie, B. 1985. Tense. Cambridge: Cam- 
bridge University Press. 
Creary, L., and Pollard, Carl. 1985. A 
computational semantics for natural language. 
ACL-85: 172-9. 
Dahl, O. 1985. Tense and Aspect Systems. 
Oxford: Basil Blackwell. 
Dowry, David. 1986. The effects of aspectual 
class on the temporal structure of discourse. In 
Dowry, 1988:37-61. 
Dowry, David. (ed.) 1986a. Tense and As- 
pect in Discourse. Linguistics and Philosophy, 
9,1. (Special issue) 
Dry, Helen. 1983. The movement of narra- 
tive time. Journal o/Literary Semantics, 12:19- 
53. 
Forbus, K. D. 1985. Qualitative process the- 
ory. In Bobrow, 1985. 
Grosz, Barbara, 1977. The representation 
ann use of focus in a .system for understand- 
ing dialogs. IJCAI-77 Proceedings, Los Altos, 
CA: Morgan Kaufmann. 
Gross, Barbara, and Candace Sidner. 1986. 
Attention, intentions and the structure of dis- 
course. Computational Linguistics, 12,3:175- 
204. 
Hayes, P. 1978. The naive physics manifesto. 
In D. Michie (Ed.), Ezpert Systen~s in the Mi- 
eroeleetronie Age. Edinburgh, Scotland: Edin- 
burgh University Press. 
Hinrichs, Erhard. 1986. Temporal anaphora 
in discourses of English. In Dowty, 1986a: 63- 
82. 
Hobbs, J. R., and R. C. Moore (Eds.). 1985. 
Formal Theories of the Coraraonsenae World. 
Norwood, NJ: Ablex Publishing Corporation. 
Hobbs, J. R. et al. 1986. Commonsense 
metaphysics and lexical semantics. ACL-86: 
231-40. 
Hopper, Paul. 1978. Aspect and foreground- 
ing in discourse. In Talmy Givon, ed., Discourse 
268 
and Syntaz. (Syntax and Semantics, voL 12.) 
New York: Academic Press. 
Hopper, Paul. 1982. (ed.) Tenae-~peet: be- 
tween Semantics and Pragmatic& Amsterdam: 
John Benjamins. 
Kamp, Hans. 1979. Events, instants and 
temporal reference. In R. Banerle, U. Egli and 
Arnim yon Stechow (eds.) Semantics from Dif- 
ferent Points of View. Berlin: Springer. 
Kamp, Hans. ms. Discourse representation 
and temporal reference. 
Kamp, Hans, and Christian Roerer. 1983. 
Tense in texts. In R. Bauerle, C. Schwarze, 
Arnim yon Stechow (eds.), Meaning, Use and 
Interpretation in Language. Berlin: De Gruyter. 
Lyons, John. 1982. Deixis and subjectivity. 
In R. Jarvelia and W. Klein (eds.) Speech, Place 
and Action. Chichester: John Wiley, 101-124. 
McDermott, Drew. 1982. A temporal logic 
for reasoning about processes and plans. Cog- 
nitive Science, 1982, 6:101-155. 
MoureL~tos, A. P. D. 1981. Events, processes, 
and states. In Tedeschi and Zaenen, 1981. 
Nakhlmovsky, A. 1986. Temporal compo- 
nents of word meanings and their coding in the 
lexicon. Proceedings of the Conference on Ad- 
vances in Lexicology, University of Waterloo. 
NakhimovskT, A. 1987. The lexicon, gram- 
matical categories and temporal reasoning. In 
Artificial Intelligence and Simulation of Behav- 
ior, Chichester:. John Wiley. 
Nakhimovsky, A. In preparation. Tense, as- 
pect and the temporal structure of the narra- 
tive. 
Partee, Barbara. 1973. Some structural 
analogies between tenses and pronouns in En- 
glish. Journal of Philosophy, 70:601-9. 
Sidner, Candace. 1983. Focusing in the com- 
prehension of definite anaphora. In l~L Brady 
and R. Berwick eds., Computational Models of 
Discourse, Cambridge, MA: MIT Press. 
Smith, Carlota. 1986. A speaker-based ap- 
proach to aspect. In Dowty, 1986a: 97-115. 
Vendler, Z. 1967. Linguistics and Philosophy. 
Ithaca, NY: Cornel\] University Press. 
Webber, Bonnie. 1987a. Event reference. In 
TINLAP-$ Position Papers. Las Cruces: New 
Mexico State University. 
Webber, Bonnie. 1987b. Two steps closer 
to event reference. TR MS-CIS-86-74, Depart- 
ment of Computer and Information Science, 
University of Pennsylvania. 
Worline, Bonnie Bess. 1956. The Children 
Who Staved Alone. New York: Scholastic Book 
Services. 
269 
