Presuppositions in Spoken Discourse

Chapter 6
approaches that focus more on the functional utility of the bridging inference,
described in the next section.
6.2.2 Functional based approaches
This second group of proposals focuses on methods to determine the anchor and
the link by recognizing the function that the connection between the sentence that
contains the anchor expression and the sentence with the bridging anaphor have.
These proposals were termed coherence approaches by Wilson & Matsui (1998). The
most well-known of these proposals have been made by Hobbs (1979), Asher &
Lascarides (1998a), and the relevance-theoretical approach advocated in Wilson &
Matsui (1998). Because Asher & Lascarides (1998a) is the most ambitious proposal
from this group, I will present it and its problems in detail.
Asher & Lascarides (1998a) define bridging as “an inference that two objects
or events that are introduced in a text are related in a particular way that isn’t
explicitly stated” (p. 83), and they then use Clark’s original inventory of
relationships. But they also go one step further and consider some indefinite NPs
to be in bridging relationships with the previous context. For example, they regard
the relationship between the plan to commit suicide and the rope in (7) to also be
bridging (taken form Asher & Lascarides1998a, p. 83, ex. (4)):
(7) Jack was going to commit suicide. He got a rope.
Resolution is intimately connected with discourse structure and Asher and
Lascarides believe that bridging is “a byproduct of computing the discourse
structure.” (p. 85). Their proposal approaches the problem of resolving bridging
inferences from two directions: an easily identified anchor can help to identify a
rhetorical relation and a rhetorical relation can help in disambiguating between two
anchors. Asher & Lascarides’ treatment distinguishes itself from other work on
bridging in that they are willing, and indeed feel it is necessary, to use different
knowledge sources depending on what is available in the context. Sometimes lexical
and world knowledge will allow a bridging inference to be resolved and then this
resolution will make a certain rhetorical relation clear. In other cases, this will not
be possible, and the rhetorical relationship computed allows the bridging inference
to be determined.
Asher & Lascarides resolve bridging inferences with the help of four metarules
or axioms that have been added to the Update function in SDRT and which
constrain the possible types of resolutions. The first of these is If Possible Use
Identity. This rule encodes the preference for binding over bridging, or in other
words, the preference for resolving the link to identity rather than to some other
type of relationship. The second meta-rule on discourse Update is that Bridges
Are Plausible and this rule should prevent overgenerating unlikely bridging
inferences even if this is a potential relationship, if this relationship does not make
sense. Asher & Lascarides discuss the possibility of restricting potential bridging
inferences to those that are defined in Clark’s original taxonomy which would then
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