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<Paper uid="E87-1042">
  <Title>TEMPORAL REASONING IN NATURAL LANGUAGE UNDERSTANDING: THE TEMPORAL STRUCTURE OF THE NARRATIVE</Title>
  <Section position="1" start_page="0" end_page="0" type="metho">
    <SectionTitle>
TEMPORAL REASONING IN NATURAL LANGUAGE UNDERSTANDING:
THE TEMPORAL STRUCTURE OF THE NARRATIVE
</SectionTitle>
    <Paragraph position="0"/>
  </Section>
  <Section position="2" start_page="0" end_page="0" type="metho">
    <SectionTitle>
CSNet: sasha@colgate
Abstract
</SectionTitle>
    <Paragraph position="0"> This paper proposes a new framework for discourse analysis, in the spirit of Grosz and Sidner (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; particularly important is the distinction between subjective, pefformative discourse and objective discourse, of which narrative is a primary example. This paper concentrates on narratives and introduces the notions of temporal focus (proposed also in Webber (1987b)) and narrative move. The processing tasks involved in reconstructing the temporal structure of a narrative (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, aspectual class and the aspectual perspective of a sentence in discourse; it is shown that in English, grammatical aspect under-determines the aspectual perspective.</Paragraph>
  </Section>
  <Section position="3" start_page="0" end_page="264" type="metho">
    <SectionTitle>
NARRATIVES
</SectionTitle>
    <Paragraph position="0"> This paper investigates the varieties of temporal knowledge and temporal reasoning that are at work in understanding extended narratives.</Paragraph>
    <Paragraph position="1"> It starts out by developing a new framework for narrative representation, a framework that has developed independently from, but is very similar to Webber, 1987a, 1987b. It also builds on the ideas of Grosz and Sidner (1986), but reformulates them specifically for the task of narrative understanding. A reformulation, I believe, is needed because different genres of discourse narrative, expository text, task-oriented dialog, argument, etc. - have different principles of organization 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.</Paragraph>
    <Paragraph position="2"> A distinction between subjective and objective modes of discourse has been drawn by many authors in linguistics and structuralist poetics, who all &amp;quot;have a category of narration to which another category is opposed; and they all agree that the non-narrative category is more subjective ~ (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 content of discourse is embedded in, and classified by, the speaker's intentions which form a hierarchical intentional structure, and (b) the content structure is separate from the attentional state, and both are rather indirectly represented by the linguistic material of discourse, organized 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 intentions is, indeed, rich and informative (note that most indirect speech acts occur in dialogs); in narratives and expository prose the intention 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 narrative or its segments is to modify the memory of the other discourse participant. Removing this, rather uninformative, top level of intention, 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 timespace. Loosely following Hayes, 1978 I use the term history-token (h-token) for all varieties of such situations (events, processes, activities, ha- null bitual actions, etc); each h-token is an instance of a hiztory-type (h-type) corresponding to abstract situations types of Situation Semantics.</Paragraph>
    <Paragraph position="3"> 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).</Paragraph>
    <Paragraph position="4"> Removing the top layer of intentions leads to other changes in the Grosz-Sidner model.</Paragraph>
    <Paragraph position="5"> Each discourse segment (DS) is now characterized by its main h-token, rather than its DS purpose. 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, crossing the threshold, closing the door (provided there is a door to open and close). Satisfaction-precedence relations between intentions correspond to the temporal and causal relations between histories. Thus re-interpreted, the pair intentional structure-attentional state of Gross and Sidner, 1986 becomes very similar to Webher's (1987a:137) proposal: aAlong with building 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 Webher 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 content, but retain Gross and Sidner's terminology for the attentional state and speak of a focus space (FS) corresponding to each DS, and a focus space stack (FS stack). An important difference 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 temporal 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, digressions and flashbacks, to which the pop-off action seems most applicable, are better represented as a move into a new FS, accompanied by a promise to return: to return to the immediately preceding FS in the case of interruptions, and to a specified position in the e/s structure in the case of digressions and flashbacks.</Paragraph>
    <Paragraph position="6"> The constancy of intention is one aspect of the narmtive's objectivity; another one is its &amp;quot;closeness unto itself&amp;quot; in the processing of definite and temporal anaphora. Subjectivity goes with deixis, the constant presence of the situation of utterance in the processing model. Objective 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 &amp;quot;narrative = and &amp;quot;non-narrative = tenses, but it is far less complete than is usually supposed: one could go through a book on computer science 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.</Paragraph>
    <Paragraph position="7"> 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 indicates relative position in time with respect to the speech event (Comrie, 1985). In dialogs tense indeed appears in its deictic function, 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 delctic. An analogy with pronouns is, perhaps, useful: although 3 person pronouns are grouped together with I and you in traditional grammars, and although they can be used deicticaUy (if strongly accented and accompanied by a gesture) their primary function is anaphoric.</Paragraph>
    <Paragraph position="8"> The anaphorlc nature of past tenses (first recognized in Partee (1973), investlg~ted specifically in narratives in Hinrichs (1986)) has important computational implications, for anaphora can only be resolved with respect to a constantly maintained and updated focus (Gross, 1977; Sidner, 1983). To emphasize the paraUel between temporal and definite anaphora, I will speak of the temporal focus of a narrative. (The same term for the same concept and  with the same motivation is proposed in Webher, 1987b; in Nakhimovsky 1986, 1987 I speak of the Active Window on discourse, or Window for short; I~mp and Rohrer, 1983 have recycled Reichenbach's Reference Point for a simihr 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 position 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.</Paragraph>
    <Paragraph position="9"> A narrative move can remain within the current 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 introduced in this section.</Paragraph>
    <Paragraph position="10"> (1) a. John entered the president's once. b.</Paragraph>
    <Paragraph position="11"> The president got up.</Paragraph>
    <Paragraph position="12"> 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 ofrice: 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 situation is anchored (cf. Barwiee and Perry, 1983) but I leave the spatial dimensions of narrative for future research.</Paragraph>
    <Paragraph position="13"> 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.</Paragraph>
    <Paragraph position="14"> (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).</Paragraph>
    <Paragraph position="15"> In (2), the similarity between definite and temporal anaphora stands out quite clearly.</Paragraph>
    <Paragraph position="16"> 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 discourse 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 beginning 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.</Paragraph>
    <Paragraph position="17"> 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.</Paragraph>
    <Paragraph position="18"> 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 focus, 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 important 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 temporal focus may be under-determined, as in (2), but there are precisely two possibilities: inside or right after the most recently narrated history. Adopting the terminology of Smith (1986) I will speak of the imperfective and perfective sentence perspective, respectively.</Paragraph>
    <Paragraph position="19"> Given the conceptual apparatus that has  been developed in this section, several tasks involved in narrative understanding can be specified. The tasks are clearly interrelated, but in this paper I make no comment on how the interaction can be set up.</Paragraph>
    <Paragraph position="20"> (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 micromove, determine the temporal relations between the histories described by the current and the preceding sentence.</Paragraph>
    <Paragraph position="21"> * b. using knowledge about durations and aspectual classes of events, determine the aspectual perspective of the new sentence and the position of the temporal focus; * e. using knowledge about causality and internal constituency of events, add inferred events to the narrated ones; update old ezpectations and set up new ones.</Paragraph>
    <Paragraph position="22"> Several kinds of temporal knowledge are thus brought to bear on the process of narrative understanding. 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 hierarchy of ~received n time cycles such as times of day, seasons of the year and the stages of human life. Second, there is compositional knowledge about internal constituency of events and their terminal points. Third, there is aspectual knowledge, both lexical, about intrinsic properties 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.</Paragraph>
  </Section>
  <Section position="4" start_page="264" end_page="265" type="metho">
    <SectionTitle>
DURATION
</SectionTitle>
    <Paragraph position="0"> 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 measurement units that are anaturaln to it: measured in a natural unit, the length of the interval 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 physical 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.</Paragraph>
    <Paragraph position="1"> 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 punctual event can only be defined relative to a time scale because awe can always 'increase the magnification' 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: instantaneous events are those that are not perceived by humans as possessing internal structure. Languages select such events for special treatment by disallowing the ~imperfectlve description B of them: one cannot use the imperfective 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 aspects 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 considerable body of literature that compares the event-process and count-mass oppositions (Mourelatos, 1981, Bunt, 1985, Bach, 1986). As I argue 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 aspectual system. (Cf. also did some reading, went  /or a v~at~ ) The distinctions event-process and processstate are thus orthogonal to each other, rather than forming a single classification as in Mourelatos, 1981; Allen, 1984. The former distinction is one of aspect: %he term 'process' means a dynamic situation viewed imperfectively, and the term 'event' means a dynamic situation viewed perfectively m (Comrie, 1976:51). The latter distinction is one of aspectual class. This is elaborated in the next section.</Paragraph>
  </Section>
  <Section position="5" start_page="265" end_page="266" type="metho">
    <SectionTitle>
ASPECT
</SectionTitle>
    <Paragraph position="0"> In what follows it is essential to keep the following three concepts apart: aspect as a grammatical category of the verb, implemented by affixes, auxillarles and such; aspectual class, which is a characteristics of an h-type or lexical meaning; the aspectual perspective of the sentence.</Paragraph>
    <Paragraph position="1"> Both grammatical aspect and aspectual class sometimes uniquely determine, sometimes just strongly constrain, the aspectual perspective.</Paragraph>
    <Paragraph position="2"> In English, the progressive aspect guarantees that the sentence perspective is imperfective; in any language, instantaneous events are presented perfectively (which does not mean that the corresponding verbs are in any sense perfective). All three concepts are needed for understanding the workings of aspectual systems; I don't think anybody in the abundant recent literature on aspect keeps all three clearly apart.</Paragraph>
    <Paragraph position="3"> There are languages, most notably Slavic, where the difference in the sentence perspective is hard-wired into verb morphology: simplifying slightly, every Russian verb is either perfecrive or imperfective, and the morphological feature of the verb determines the aspectual perspective 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 result from interactions between this (pragmatically defined) Grundbsdeutung and numerous other factors, including aspectual class, discourse genre, and general pragmatic principles of language.</Paragraph>
    <Paragraph position="4"> The following examples, adopted from Dowty (1986), illustrate the interplay between aspect,  aspectual class and the micro-move of the narrative. (I repeat (1) here for convenience.) (1) a. John entered the president's office, b.</Paragraph>
    <Paragraph position="5"> The president got up.</Paragraph>
    <Paragraph position="6"> (5) a. John entered the president's office, b.</Paragraph>
    <Paragraph position="7"> The president was asleep, c. The clock on the wall ticked loudly.</Paragraph>
    <Paragraph position="8"> (6) a. John entered the president's office, b.</Paragraph>
    <Paragraph position="9">  The president was writing a letter.</Paragraph>
    <Paragraph position="10"> Sentences (la) and (lb) describe two processes (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, following Comrie (1976), tellc processes.) The aspectual 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.</Paragraph>
    <Paragraph position="11"> 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 temporal 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).</Paragraph>
    <Paragraph position="12"> 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.</Paragraph>
    <Paragraph position="13"> When it came to be recognized that progressive 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 current 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 perspective is peffective and the temporal focus advances. 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:  -&amp;quot; ? (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.</Paragraph>
    <Paragraph position="14"> Other examples of micro-moves that violate Hinrichs' rule are given in (8) and (9), quoted from Dowty, 1986. (The rule can also be violated by a macro-move, as in example (2)).</Paragraph>
    <Paragraph position="15"> (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 (morphological) peffective; it has a marked impeffective and an unmarked default that does not provide substantial information about the aspectual perspective of the sentence (cf. Dahl, 1985 for the same view). In other words, English morphology, 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 extensive empirical investigation could, I believe, produce a full catalog of micro-moves commonly employed in Western narratives.</Paragraph>
  </Section>
  <Section position="6" start_page="266" end_page="267" type="metho">
    <SectionTitle>
ASPECTUAL CLASS
</SectionTitle>
    <Paragraph position="0"> The major division among non-instantaneous histories, recognized at least since Aristotle, is between process (energela) and state (stasis). In recent times, Vendler (1967) proposed a highly influential classification that is still commonly accepted, although the principles of classification have changed. Vendler believed, erroneously, 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 statives, such as know, don't). In the model-theoretical version of Taylor and Dowry, the classification is based on the relationship between the truth value of a sentence at an interval and at its subintervals; so, for instance, a sentence S is stative (denotes a state) iff it follows from the truth of S at an interval I that S is true at all subintervals of I. (Dowty, 1986:42).</Paragraph>
    <Paragraph position="1"> I submit that these criteria cannot possibly be right, i.e. capture the real distinctions operative in the workings of human language: these have to relate to something perceived and experienced, 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 truthfully 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 processes and states seriously, and classify historles according to their internal dynamics, the stability 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 distinction 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.</Paragraph>
    <Paragraph position="2"> Resource-consuming states all seem to require 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 require process-specific resources as well: reading, for example, requires not only being awake and not too hungry, but also a text to read.</Paragraph>
    <Paragraph position="3"> 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 between them, building a house consumes the asyet-unbuilt but envisioned part of it, and destroying 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 object, and moving a specified amount of material (possibly the mover himself) to a specified destination. A subclass of destruction processes are ingestions, which convert an external resource into an internal one. Moving is understood to include all three of Schank's PTRANS, ATRANS and MTRANS classes, with the proviso that, unlike physical motion, MTRANS really copies structures from the source to the destination. Moving also includes gradual (but not  instantaneous) changes of state.</Paragraph>
    <Paragraph position="4"> Lacking internal structure, instantaneous events have to be classified by comparing the world before 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.</Paragraph>
    <Paragraph position="5"> The resulting classification, discussed in Nakhimovsky, 1987, captures linguistically significant distinctions: for instance, most English verbs describing instantaneous events fall into those groups where the instantaneous event meets a state.</Paragraph>
  </Section>
class="xml-element"></Paper>