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<Paper uid="P99-1006">
  <Title>Discourse Relations: A Structural and Presuppositional Account Using Lexicalised TAG*</Title>
  <Section position="4" start_page="45" end_page="46" type="metho">
    <SectionTitle>
4 Otherwise
</SectionTitle>
    <Paragraph position="0"> Our analysis of &amp;quot;otherwise&amp;quot; assumes a modal semantics broadly following Kratzer (1991 ) and Stone (1999), where a sentence is asserted with respect to a set of possible worlds. The semantics of &amp;quot;otherwise ct&amp;quot; appeals to two sets of possible worlds. One is W0, the set of possible worlds consistent with our knowledge of the real world. The other, Wp, is that set of possible worlds consistent with the condition C that is presupposed, t~ is then asserted with respect to the complement set Wo - Wp. Of interest then is C - what it is that can serve as the source licensing this presupposition. 7 There are many sources for such a presupposition, including if-then constructions (Example 7a7b), modal expressions (Examples 7c- 7d) and infinitival clauses (Example 7e)  (7) a. If the light is red, stop. Otherwise, go straight on.</Paragraph>
    <Paragraph position="1"> b. If the light is red, stop. Otherwise, you might get run over c. Bob \[could, may, might\] be in the kitchen.</Paragraph>
    <Paragraph position="2"> Otherwise, try in the living room.</Paragraph>
    <Paragraph position="3"> d. You \[must, should\] take a coat with you.</Paragraph>
    <Paragraph position="4"> Otherwise you'll get cold.</Paragraph>
    <Paragraph position="5"> e. It's useful to have a fall-back position. Otherwise you're stuck.</Paragraph>
    <Paragraph position="6">  other respects&amp;quot;, which appears either as an adjective phrase modifier (e.g. &amp;quot;He's an otherwise happy boy.&amp;quot;) or a clausal modifier (e.g., &amp;quot;The physical layer is different, but otherwise it's identical to metropolitan networks.&amp;quot;). What is presupposed here are one or more actual properties of the situation under discussion.</Paragraph>
    <Paragraph position="7"> each of which introduces new possibilities that are consistent with our knowledge of the real world (W0), that may then be further described through modal subordination (Roberts, 1989; Stone and Hardt, 1999).</Paragraph>
    <Paragraph position="8"> That such possibilities must be consistent with Wo (i.e., why the semantics of &amp;quot;otherwise&amp;quot; is not simply defined in terms of W r) can be seen by considering the counterfactual variants of 7a-7d, with &amp;quot;had been&amp;quot;, &amp;quot;could have been&amp;quot; or &amp;quot;should have taken&amp;quot;. (Epistemic &amp;quot;must&amp;quot; can never be counterfactual.) Because counterfactuals provide an alternative to reality, W e is not a subset of W0 - and we correctly predict a presupposition failure for &amp;quot;otherwise&amp;quot;. For example, corresponding to 7a we have: (8) If the light had been red, John would have stopped. #Otherwise, he went straight on.</Paragraph>
    <Paragraph position="9"> The appropriate connective here - allowing for what actually happened - is &amp;quot;as it is&amp;quot; or &amp;quot;as it was&amp;quot;. 8 As with &amp;quot;for example&amp;quot;, &amp;quot;otherwise&amp;quot; is compatible with a range of additional relations linking discourse together as a product of discourse structure and defeasible inference. Here, the clauses in 7a and 7c provide a more complete description of what to do in different circumstances, while those in 7b, 7d and 7e involve an unmarked &amp;quot;because&amp;quot;, as did Example 2d. Specifically, in 7d, the &amp;quot;otherwise&amp;quot; clause asserts that the hearer is cold across all currently possible worlds where a coat is not taken. With the proposition understood that the hearer must not get cold (i.e., that only worlds where the hearer is not cold are compatible with what is required), this allows the inference (modus tollens) that only the worlds where the hearer takes a coat are compatible with what is required. As this is the proposition presented explicitly in the first clause, the text is compatible with an inferential connective like &amp;quot;because&amp;quot;. (Similar examples occur with &amp;quot;epistemic&amp;quot; because.) Our theory correctly predicts that such discourse relations need not be left implicit, but can instead be explicitly signalled by additional connectives, as in 8There is a reading of the conditional which is not counterfactual, but rather a piece of free indirect speech reporting on John's train of thought prior to encountering the light. This reading allows the use of &amp;quot;otherwise&amp;quot; with John's thought providing the base set of worlds W0, and &amp;quot;otherwise&amp;quot; then introducing a complementary condition in that same context: If the light had been red, John would have stopped.</Paragraph>
    <Paragraph position="10"> Otherwise, he would have carded straight on. But as it turned out, he never got to the light.</Paragraph>
    <Paragraph position="11">  (9) You should take a coat with you because otherwise you'll get cold.</Paragraph>
    <Paragraph position="12">  and earlier examples.</Paragraph>
    <Paragraph position="13"> (Note that &amp;quot;Otherwise P&amp;quot; may yield an implicature, as well as having a presupposition, as in (10) John must be in his room. Otherwise, his light would be off.</Paragraph>
    <Paragraph position="14"> Here, compositional semantics says that the second clause continues the description of the situation partially described by the first clause. General inference enriches this with the stronger, but defeasible conclusion that the second clause provides evidence for the first. Based on the presupposition of &amp;quot;otherwise&amp;quot;, the &amp;quot;otherwise&amp;quot; clause asserts that John's light would be off across all possible worlds where he was not in his room. In addition, however, implicature related to the evidence relation between the clauses, contributes the conclusion that the light in John's room is on. The point here is only that presupposition and implicature are distinct mechanisms, and it is only presupposition that we are focussing on in this work.</Paragraph>
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