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<Paper uid="J92-4007">
  <Title>Mann, William C., and Thompson,</Title>
  <Section position="2" start_page="539" end_page="539" type="metho">
    <SectionTitle>
2. The Argument from Interpretation
</SectionTitle>
    <Paragraph position="0"> We begin by showing that in discourse interpretation, recognition may flow from the informational level to the intentional level or vice versa. In other words, a hearer may be able to determine what the speaker is trying to do because of what the hearer knows about the world or what she knows about what the speaker believes about the world. Alternatively, the hearer may be able to figure out what the speaker believes about the world by recognizing what the speaker is trying to do in the discourse. This point has previously been made by Grosz and Sidner (1986, pp. 188-190). 4 Returning to our initial example Example 1  (a) George Bush supports big business.</Paragraph>
    <Paragraph position="1"> (b) He's sure to veto House Bill 1711.</Paragraph>
    <Paragraph position="2">  suppose that the hearer knows that House Bill 1711 places stringent environmental controls on manufacturing processes, s From this she can infer that supporting big business will cause one to oppose this bill. Then, because she knows that one way for the speaker to increase a hearer's belief in a proposition is to describe a plausible cause of that proposition, she can conclude that (a) is intended to increase her belief in (b), i.e., (a) is evidence for (b). The hearer reasons from informational coherence to intentional coherence.</Paragraph>
    <Paragraph position="3"> Alternatively, suppose that the hearer has no idea what House Bill 1711 legislates. However, she is in a conversational situation in which she expects the speaker to support the claim that Bush will veto it. For instance, the speaker and hearer are arguing and the hearer has asserted that Bush will not veto any additional bills before the next election. Again using the knowledge that one way for the speaker to increase her belief in a proposition is to describe a plausible cause of that proposition, the hearer in this case can conclude that House Bill 1711 must be something that a big business supporter would oppose--in other words that (a) may be a cause of (b). Here the reasoning is from intentional coherence to informational coherence. Note that this situation illustrates how a discourse can convey more than the sum of its parts. The speaker not only conveys the propositional content of (a) and (b), but also the implication relation between (a) and (b): supporting big business entails opposition to House Bill 1711. 6 It is clear from this example that any interpretation system must be capable of recognizing both intentional and informational relations between discourse elements, and must be able to use relations recognized at either level to facilitate recognition at the other level. We are not claiming that interpretation always depends on the recognition of relations at both levels, but rather that there are obvious cases where it does. An interpretation system therefore needs the capability of maintaining both levels of relation.</Paragraph>
  </Section>
  <Section position="3" start_page="539" end_page="540" type="metho">
    <SectionTitle>
4 In Grosz and Sidner (1986), dominates and satisfaction-precedence are the intentional relations, while
</SectionTitle>
    <Paragraph position="0"> supports and generates are the informational relations. 5 The hearer also needs to believe that it is plausible the speaker holds the same belief; (see Konolige and Pollack 1989). 6 This is thus an example of what Sadock calls modus brevis (Sadock 1977).</Paragraph>
    <Paragraph position="1">  Johanna D. Moore and Martha E. Pollack A Problem for RST 3. The Argument from Generation  It is also crucial that a generation system have access to both the intentional and informational relations underlying the discourses it produces. For example, consider the following discourse: S: H:  (a) Come home by 5:00. (b) Then we can go to the hardware store before it closes.</Paragraph>
    <Paragraph position="2"> (c) We don't need to go to the hardware store. (d) I borrowed a saw from  Jane.</Paragraph>
    <Paragraph position="3"> At the informational level, (a) specifies a CONDITION for doing (b): getting to the hardware store before it closes depends on H's coming home by 5:00. 7 How should S respond when H indicates in (c) and (d) that it is not necessary to go to the hardware store? This depends on what S's intentions are in uttering (a) and (b). In uttering (a), S may be trying to increase H's ability to perform the act described in (b): S believes that H does not realize that the hardware store closes early tonight. In this case, S may respond to H by saying: S: (e) OK, I'll see you at the usual time then.</Paragraph>
    <Paragraph position="4"> On the other hand, in (a) and (b), S may be trying to motivate H to come home early, say because S is planning a surprise party for H. Then she may respond to H with something like the following: S: (f) Come home by 5:00 anyway. (g) Or else you'll get caught in the storm that's moving in.</Paragraph>
    <Paragraph position="5"> What this example illustrates is that a generation system cannot rely only on informational level analyses of the discourse it produces. This is precisely the point that Moore and Paris have noted (1992). If the generation system is playing the role of S, then it needs a record of the intentions underlying utterances (a) and (b) in order to determine how to respond to (c) and (d). Of course, if the system can recover the intentional relations from the informational ones, then it will suffice for the system to record only the latter. However, as Moore and Paris have argued, such recovery is not possible because there is not a one-to-one mapping between intentional and informational relations.</Paragraph>
    <Paragraph position="6"> The current example illustrates this last point. At the informational level, utterance (a) is a CONDITION for (b), but on one reading of the discourse there is an ENABLEMENT relation at the intentional level between (a) and (b), while on another reading there is a MOTIVATION relation. Moreover, the nucleus/satellite structure of the informational level relation is maintained only on one of these readings. Utterance (b) is the nucleus of the CONDITION relation, and, similarly, it is the nucleus of the ENABLEMENT relation on the first reading. However, on the second reading, it is utterance (a) that is the nucleus of the MOTIVATION relation.</Paragraph>
  </Section>
  <Section position="4" start_page="540" end_page="541" type="metho">
    <SectionTitle>
7 See Mann and Thompson (1987) for definitions of the RST relations used throughout this example.
</SectionTitle>
    <Paragraph position="0"> Computational Linguistics Volume 18, Number 4 Just as one cannot always recover intentional relations from informational ones, neither can one always recover informational relations from intentional ones. In the second reading of the current example, the intentional level MOTIVATION relation is realized first with a CONDITION relation between (a) and (b), and, later, with an OTHERWISE relation in (f) and (g).</Paragraph>
  </Section>
  <Section position="5" start_page="541" end_page="542" type="metho">
    <SectionTitle>
4. Discussion
</SectionTitle>
    <Paragraph position="0"> We have illustrated that natural language interpretation and natural language generation require discourse models that include both the informational and the intentional relations between consecutive discourse elements. RST includes relations of both types, but commits to discourse analyses in which a single relation holds between each pair of elements.</Paragraph>
    <Paragraph position="1"> One might imagine modifying RST to include multi-relation definitions, i.e., definitions that ascribe both an intentional and an informational relation to consecutive discourse elements. Such an approach was suggested by Hovy (1991), who augmented rhetorical relation definitions to include a &amp;quot;results&amp;quot; field. Although Hovy did not cleanly separate intentional from informational level relations, a version of his approach might be developed in which definitions are given only for informational (or, alternatively, intentional) level relations, and the results field of each definition is used to specify an associated intentional (informational) relation. However, this approach cannot succeed, for several reasons.</Paragraph>
    <Paragraph position="2"> First, as we have argued, there is not a fixed, one-to-one mapping between intentional and informational level relations. We showed, for example, that a CONDITION relation may hold at the informational level between consecutive discourse elements at the same time as either an ENABLEMENT or a MOTIVATION relation holds at the intentional level. Similarly, we illustrated that either a CONDITION or an OTHERWISE relation may hold at the informational level at the same time as a MOTIVATIONAL relation holds at the intentional level.</Paragraph>
    <Paragraph position="3"> Thus, an approach such as Hovy's that is based on multi-relation definitions will result in a proliferation of definitions. Indeed, there will be potentially n x m relations created from a theory that initially includes n informational relations and m intentional relations. Moreover, by combining informational and intentional relations into single definitions, one makes it difficult to perform the discourse analysis in a modular fashion. As we showed earlier, it is sometimes useful first to recognize a relation at one level, and to use this relation in recognizing the discourse relation at the other level.</Paragraph>
    <Paragraph position="4"> In addition, the multi-relation definition approach faces an even more severe challenge. In some discourses, the intentional structure is not merely a relabeling of the informational structure. A simple extension of our previous example illustrates the point: S: (a) Come home by 5:00. (b) Then we can go to the hardware store before it closes. (c) That way we can finish the bookshelves tonight.</Paragraph>
    <Paragraph position="5"> A plausible intentional level analysis of this discourse, which follows the second reading we gave earlier, is that finishing the bookshelves (c) motivates going to the hardware store (b), and that (c) and (b) together motivate coming home by 5:00 (a).</Paragraph>
    <Paragraph position="6"> Coming home by 5:00 is the nucleus of the entire discourse: it is the action that S  Johanna D. Moore and Martha E. Pollack A Problem for RST wishes H to perform (recall that S is planning a surprise party for H). This structure is illustrated below: motivation motivation b c At the informational level, this discourse has a different structure. Finishing the bookshelves is the nuclear proposition. Coming home by 5:00 (a) is a condition on going to the hardware store (b), and together these are a condition on finishing the bookshelves (c): condition a c The intentional and informational structures for this discourse are not isomorphic. Thus, they cannot be produced simultaneously by the application of multiple-relation definitions that assign two labels to consecutive discourse elements. The most obvious &amp;quot;fix&amp;quot; to RST will not work. RST's failure to adequately support multiple levels of analysis is a serious problem for the theory, both from a computational and a descriptive point of view.</Paragraph>
  </Section>
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