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<Paper uid="P91-1053">
  <Title>RESOLVING A PRAGMATIC PREPOSITIONAL PHRASE ATTACHMENT AMBIGUITY</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1. Introduction
</SectionTitle>
    <Paragraph position="0"> To resolve or not to resolve, that is the structural ambiguity dilemma. The traditional wisdom is to disambiguate only when it matters in terms of the meaning of the utterance, and to do so using the computationally least costly information.</Paragraph>
    <Paragraph position="1"> NLP work on PP-attachment has followed this wisdom, and much effort has been focused on formulating structural and lexical strategies for resolving noun-phrase and verb-phrase (NP-PP vs. VP-PP) attachment ambiguity (e.g. \[8, 11\]). In one study, statistical analysis of the distribution of lexical items in a very large text yielded 78% correct parses while two humans achieved just 85%\[5\]. The close performance of machine and human led the authors to pose two issues that will be addressed in this paper: is the predictive power of distributional data due to &amp;quot;a complementation relation, a modification relation, or something else&amp;quot;, and what characterizes the attachments that escape prediction? 2. Pragmatically ambiguous PPs Although structural and lexical rules alone do not suffice to disambiguate all kinds of PPs, discourse modelling is viewed as computationally costly (cf. \[1\]). The debate over resolution strategies is not simply about practicality, but rather, at stake is the notion of what exactly it means for a PP to attach. This paper defends discourse-level strategies by arguing that a certain PP-attachment ambiguity, sentential vs. verb-phrase (S-PP vs. VP-PP), reflects a third kind of relation that is pragmatic in nature. As noted in \[11\], context-dependent preferences cannot be computed a priori, so pragmatic PP-attachment ambiguities are among those that defy structural and lexical rules for disambiguation.</Paragraph>
    <Paragraph position="2"> Another criticism aimed at discourse-level approaches is that pragmatic ambiguities can be left unresolved because they do not affect the meaning of an utterance. In the case of S-PPs and VP-PPs, however, the linguistic evidence points to significant meaning differences (section 3). This paper offers a unified account of the linguistic behavior of these PPs which is expressed in a new formalism (section 4), and concludes that the resolution of pragmatic PP-attachment ambiguity is necessary for language understanding (section 5).</Paragraph>
  </Section>
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