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<Paper uid="W93-0227">
  <Title>Rhetoric as Knowledge</Title>
  <Section position="2" start_page="0" end_page="102" type="metho">
    <SectionTitle>
1 Communicative Intentions
</SectionTitle>
    <Paragraph position="0"> It is commonly assumed that in engaging in communication, tile speaker 1 (S) has a specific communicative intention. Communicative intentions relate to that domain that the use of language can affect, namely the mental state of the hearer (H), i.e., H's beliefs, desires, and intentions. Of course, S may have other intentions that relate to tile world at large (such as to get H to open a window), but these are not properly speaking eonnnunicative intentions: they can only be achieved by use of language if language first produces some appropriate change in H's mental states.</Paragraph>
    <Paragraph position="1"> In discussing the ways in which S's use of language can affect H's mental states, it is important to make a distinction between the fact that H is entertaining a belief, desire, or intention, and the degree or strength with which it is entertained. This distinction has not always been made in the text generation literature; presumably, this is because for the types of texts whose generation has been studied, namely reports, documentation, and manuals of various kinds, this distinction is not relevant. This is because these texts (weather reports, military reports, instruction manuals, and so on) are &amp;quot;authoritative text.s&amp;quot;: if the text makes H entertain a certain belief or intention, then H will do so with a sufficient strength to satisfy S's communicative goals.</Paragraph>
    <Paragraph position="2"> I claim that the interesting aspects of rhetorical relations (or &amp;quot;rhetoric&amp;quot; for short), and the intersting role that rhetoric can play in discourse generation, have not been studied because the types of text analyzed and generated have been one-sided in significant respects. For the sake of concreteness, let us assume the following definition: *Department of CIS, University of Pennsylvania, Philadelphia PA 19104. ramb0u@unagi.cis.upenn.edu. This work was partially supported by the following grants: ARO DAAL 03-89-C-0031; DARPA N00014-90-J-1863; NSF ll~I 90-16592; and Ben Franklin 91S.3078C-I.</Paragraph>
    <Paragraph position="3"> ! I use the terminology fi'om spoken language; these remarks apply equally well to written language.</Paragraph>
    <Paragraph position="4">  Rhetoric is S's knowledge of how text structure manipulates tile strength of beliefs, desires, and intentions already entertained by H.</Paragraph>
    <Paragraph position="5"> In order to argue that this definition makes sense, I will discuss three questions: is rhetoric necessary, is it trivial, and is it useful?</Paragraph>
  </Section>
  <Section position="3" start_page="102" end_page="102" type="metho">
    <SectionTitle>
2 Is Rhetoric Necessary?
</SectionTitle>
    <Paragraph position="0"> More precisely, I will discuss whether S must necessarily have access to rhetoric in order to comnmnicate effectively. S can only affect H's mental state through the use of a text (the sequence of utterances which constitute an act of communication), which means that it is in the act of decoding the text that H is affected. Thus S's goal is that H be affected by the text. In order to achieve this goal, S nmst know about the process of decoding that I1 will use, otherwise S carmot purposefully use language. Does text structure contribute to affecting H? Consider the following discourses (uttered in a context where S knows that H does not like paying taxes under any circumstance).</Paragraph>
    <Paragraph position="1">  (1) Vote for Bush. Clinton will raise taxes. Bush will not raise taxes.</Paragraph>
    <Paragraph position="2"> (2) Clinton will raise taxes. Vote for Bush. Bush will not raise taxes.</Paragraph>
    <Paragraph position="3"> (2) is arguably less convincing than (1) since tile the two sentences about tim candidates' attitude  towards taxation are not juxtaposed, thus depriving them of their contra.stive force. Since text structure participates in affecting H, then S must have knowledge about tile mechanism; i.e., S must have access to rhetoric.</Paragraph>
  </Section>
  <Section position="4" start_page="102" end_page="102" type="metho">
    <SectionTitle>
3 Is Rhetoric Trivial?
</SectionTitle>
    <Paragraph position="0"> It has often been observed that many of tile definitions of rhetorical relations are tautologous.</Paragraph>
    <Paragraph position="1"> Consider, for example, RST's definition of EVIDENCE \[Mann and TholnpSOlL 1987, p.10\]. 'Nuc' refers to the nucleus, that for which evidence is being contributed, and 'Sat' refers to the satellite, tile evidence. Nuc and Sat, are assumed to be juxtaposed.</Paragraph>
    <Paragraph position="2">  The definition of COUNTER-EVIDENCE is entirely similar to (and as tautologous as) that of EV-IDENCE, but it does not yield a coherent discourse. Consider the following, uttered in the same context as (1) and (2) above: (3) Clinton will lower taxes. No democratic president has ever lowered taxes.</Paragraph>
    <Paragraph position="3"> There is no coherent reading for (3) under which S wants to decrease H's belief in the first sentence. In order to achieve this effect, S needs to explicitly negate the first clause, which results in an EVIDENCE relation.</Paragraph>
    <Paragraph position="4"> (4) Clinton will not lower taxes. No democratic president has ever lowered taxes. Thus, the contribution of rhetoric lies in detailing what sort of effects (on It's beliefs, desire, and intentions) mere juxtaposition can achieve. The fact that not all possible effects can be achieved without explicit lexical and syntactic means is what makes rhetoric an important body of knowledge in discourse processing.</Paragraph>
  </Section>
  <Section position="5" start_page="102" end_page="104" type="metho">
    <SectionTitle>
4 Is Rhetoric Useful?
</SectionTitle>
    <Paragraph position="0"> More specifically, can rhetoric be used in discourse planning? From what has been said, it would follow that rhetoric is essential in discourse planning, since without rhetoric, S would have no knowledge of the effects of the discourse structure on H. But can rhetoric, as defined here, in fact be used for discourse planning? Text planning architectures using knowledge about the relationship between communicative intentions and the juxtaposition of discourse segments have been developed at ISI \[Hovy, 1988\]. 1 conjecture that tiffs type of architecture is well suited for planning texts (or those aspects of texts) that manipulate the strength with which H entertains beliefs, desires, and intentions. Such a plalmer would require a more sophisticated representation of mental states:  1. A logic of desire and a logic of intentions are required. Tile logic of desire would most likely he a modal logic; the logic of intentions wouhl, presmnably, require a representation of action.</Paragraph>
    <Paragraph position="1"> 2. For beliefs, desires, and intentious, the strength with which they are entertained must also be  represented. Strength can be represented by discrete indications of quality, as has been done by \[Walker, 1993\] in conversational models.</Paragraph>
    <Paragraph position="2"> Ideal applications of such a planner would include texts whose primary goal is to increase H's desire to perform a certain action, such as advertising texts of tile types given above. Furthermore, dialog  planning is more likely to yield interesting instances of the use of rhetoric, since in monologic genres the modeling of the strength of H's beliefs, desires, and intentions must remain conjectural, while in dialogic genres, H's feedback can contribute to S's assessment of H's mental state.</Paragraph>
    <Paragraph position="3"> Rhetoric is not useful for texts whose goal is mainly or exclusively to convey information, and for which H is assumed to stroTtgly believe any proposition the text makes H entertain. This is typically the case for reports, including those generated by the original ISI planner. The use of a rhetoric-based top-down planner for planning such texts cannot be successful \[Kittredge et al., 1991\], since here the decomposition of the communicative goal nmst refer to the domain structure, and therefore is too unconstrained to be handled by a domain-independent body of knowledge.</Paragraph>
    <Paragraph position="4"> 5 Types of Intentions, Types of Relations, Types of Texts The distinction that has been made throughout this paper, between making H entertain a belief, desire, or intention, and increasing the strength with which it is entertained, corresponds to the one between intentional/presentational and informational/subject matter relations made by \[Mann and Thompson, 1987\], and recently discussed by \[Moore and Pollack, 1992\]. Rhetoric relates to the intentional level - note that the effect of RST's presentational relations are all formulated in terms of increasing the strength of some aspect of H's mental state, while the subject matter relations all have the effect of making H entertain (&amp;quot;recognize&amp;quot;) new beliefs. Texts that do not have a meaningful intentional level, such as reports, cannot be planned using a rhetoric-based planner. Texts that only have an intentional level of structure, such as (1) above, are ideally suited for such planners. However, as Moore and Pollack argue, many texts simultaneously have both types of structure. For such texts, new planning architectures must be found. They will require a better understanding of comlnunicative goals along the lines argued for in this paper.</Paragraph>
  </Section>
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