2. relying on the fact that variable names are unique, read off the binds-constraints from theMRS;
3. MRSs underspecify the order of conjuncts by putting conjoined relations on the same label, this has to be translated into n!−1 LL-formulae (with n being the number of conjuncts) with binary-trees rooted in∧; and finally,
4. inMRSs, the scope-constraints are notationally separated from theEPs; we simply con-join these.
One final thing that is different inMRS, however, is that (Copestake et al. 1999) uses a stricter constraint to express scope-relations than the outscopes we have used. They define a variant of outscopes which they call qeq (written=q), which stands for ‘equality modulo quantifiers.’ To give an example of its intended semantics, for l1=ql2to be true there can only be quantifiers ‘between’ l1and l2, other scope-bearing relations are not allowed to intervene. For our purposes this constraint is too strict. As discussed above in the section of ADV-fragments and modified fragments, we have to allow other scope-bearing elements (for example modals) to intervene. Hence, we must use the more general outscopes-constraint.
We close this section with a side remark. (Copestake et al. 1999) claims that the stricter scope-constraint they use simplifies construction; for this claim, however, they do not give any evidence. According to (Flickinger, p.c.), the evidence for having this stricter constraint is given by some German examples which can only be handled if qeq is available. We will not further discuss this here, and simply use geq (standing for ‘greater or equal’, i.e. for our outscopes relation) in our representations, regardless of of whether theERGfor example really needs qeq or not.
A Coherence-Based Approach II: A Grammar of Fragments
In this chapter we show how the representations of the compositional semantics of fragments that we have introduced in the previous chapter can be built on the syntax/semantics-interface. Before we do this, however, we take a step back and discuss in a more abstract way the relative merits of two strategies for describing the syntactic form of fragments: either as phrases that somehow get the same status as sentences, i.e. are allowed to ‘stand alone’ by the grammar; or as special kinds of sentence-constructions.
We will give arguments in favour of the latter strategy, and then turn to implementing it. We first show howMRSs—the structures we introduced in the previous chapter as short-hands for our more detailed LL-representations—can be represented and built in feature structure based grammars in general; then in Section 7.3 we develop in detail ourHPSG-encoding of the construction type ‘fragment’. In Sec-tion 7.4 we describe our implementaSec-tion of the rules and evaluate it under real-world condiSec-tions.
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7.1 What is the syntactic form of fragments?
In this section we discuss the relative merits of two strategies for describing the syntactic form of frag-ments, namely either as phrases that somehow get the same status as sentences, in that they are allowed by the grammar to ‘stand alone’; or as special kinds of sentence-constructions. So the question we’re trying to answer here is: what are fragments, syntactically? What is (270-b), for example? Is it a sentence?
(270) a. Who came to the party?
b. Peter.
Clearly, (270-b) conveys a message; this observation was the starting point for our investigation into the phenomenon “fragment”. Does that make it a sentence, though? What is a sentence, anyway? This, surprisingly, turns out to be quite a controversial question. Take this definition from a dictionary of lin-guistics (Matthews 1997, p.337): “Usually conceived [. . . ] as the largest unit of grammar, or the largest unit over which a rule of grammar can operate.” (270-b) obviously falls short of this definition; after all, it is just an NP, and they are not the largest units of grammar. The following remark from an introduct-ory syntax textbook (Sag & Wasow 1999, p.72) takes a slightly different angle: “Somewhere along the line, of course, an adequate grammar will need to specify the well-formed ‘stand-alone’ utterances of the language: the phrases that can be used in isolation to express a complete message are those whose mother is of the category ‘S’.” Now, (270-b) does express a complete message, but does it do that ‘in isolation’? Well, it clearly doesn’t, but neither do sentences like those in (271). So, what now?
(271) a. She hates him.
b. He does, too.
What is causing the confusion here is the mixture in these definitions of syntactic notions (sentence) and semantic or pragmatic ones (can stand alone). The question is what is to be seen as primary: if sentences are defined as those expressions that convey messages, then (270-b) is a sentence; we can however also choose to give this up as a distinctive feature of sentences, and allow other phrases, like the NP in (270-b), to ‘stand alone’.
Let’s bring this question down from this rather metaphysical level to a more technical one: what is the right parse for fragments? Is it enough to parse them as the phrases they are, or do we need to do more?1 Or, in the terminology of (Morgan 1973), as reviewed in Chapter 4, are fragments ‘base-generated’, or is something else at work? What are the consequences of either decision?
1Of course, in the previous chapter we have actually already decided on our answer to this question, by spending much effort on defining constraints that help to formalise a semantics for such fragments that is quite different from that of the phrase itself.
So we will only add more arguments here in favour of this decision, and look briefly into a differing analysis.
We first look at the option of allowing all kinds of phrases as ‘stand-alone’ utterances; this approach, as mentioned above, is advocated for example by (Barton 1990).2Following this strategy, we can imagine an approach that assigns our fragment (270-b) the logical form (272). The first advantage of such an approach is that we do not have to change any rules on the syntax/semantics interface; this phrase gets the same interpretation as a fragment as it gets as part of a larger phrase.
(272) λP.P(p)
However, as already discussed in Section 6.2, one disadvantage of such an approach is that these rep-resentations do not encode the information that there is a difference between fragments and phrases, namely that the intended meaning of the former is of a different type than the meaning of the latter.
Such an approach must leave the task of recognising this entirely to pragmatics. We further claimed that it complicates the discourse processing, since now fragments can be of all sorts of semantic types, and so the speech-act rules would have to additionally account for that. Finally, pragmatics would then have to reason with logical forms (and all their consequences) themselves; given the need for consistency checks in pragmatic reasoning this would make it uncomputable.
These are semantic and pragmatic arguments against this strategy, but we can also find quite convincing syntactic arguments that favour a syntactic analysis of fragments as (special kinds of) sentences. (273-a) shows a phenomenon that has been called ‘sluicing’ by (Ross 1969): a wh-phrase as a complement to a verb.
(273) a. I don’t know where.
b. Where?
c. I don’t know where Peter is.
d. *I don’t know in the park.
We will analyse this construction as involving our Elabq-fragments from Chapter 2,3,4 and so the
‘where’ in (273-a) is analysed in the same way as that in (273-b). As (273-c) shows, ‘know’ can take a full sentence as a complement, in this case “where Peter is”.5 It can not, however, take a PP as
com-2We said above that her arguments in favour of this approach are very (GB-)theory dependent, and so not really relevant for our discussion here.
3(Ginzburg & Sag 2001) similarly analyse such sluices as embedded fragments.
4In fact, Ross’s (1969) original sentence examples, e.g. (i-a), seem to us simply to give a confirmation that a condition on question-asking holds (namely that the questioner does not know the answer), which is required because of implicatures that it might not.
(i) a. There’s a party but I don’t know where.
b. There’s a party.. But, where?
Someone who knows that there is a party is also likely to know where, and the violation of this expectation in (i-a) has to be explicitly signalled with a contrastive discourse particle. This is all that is required, as the reduced variant (i-b) illustrates.
5That is an inverted sentence, to be sure, but still it is a sentence in most accounts.
plement, as the ungrammaticality of (273-d) demonstrates. This strongly favours a syntactic analysis of the embedded fragment “where” in (273-a), and hence of (273-b) as well, as a sentence, and not a PP.
A similar argument can be made with short-answers. (274-a) shows a short-answer as a complement of a verb that takes sentential complements, but not NP-complements.6
(274) A: Who will do this?
a. B: John said Peter.
b. B: John said (that) Peter will do this.
So to summarise, there are good syntactic and semantic reasons to parse fragments as sentences. But how shall we do this? How do we express that there are (syntactic) elements ‘missing’? There are again two options here: we could posit phonologically empty elements that occupy the missing positions, or we could devise special constructions that take phrases to sentence-level. Take fragment (270-b) again, repeated here in dialogue (275).
(275) a. Who came to the party?
b. Peter.
The fragment is resolved in this context to something that can be paraphrased as “Peter came to the party.”—i.e., the fragment fills a subject position. This could lead us to conclude that there is a VP
‘missing’ in (275-b), and to analyse the syntactic structure of (275-b) as shown in (276).
(276) [S[NPPeter] [V P /0] ]
However, that would force us in (277-a) to analyse what seems to be the same fragment differently syntactically, in the way illustrated by (277-b)—and again differently for examples where the fragment is resolved to be a complement of an NP for example, or as an adjunct. This is clearly not desirable, and so we decide against this strategy.
(277) a. A: Who does Kim like?
B: Peter.
b. [S[NP/0] [V P[V/0] [NPPeter] ] ]
6The situation is not as unambiguous here as in (273), though, since one could claim that the short-answer in (274-a) is only quoted (but cf. “John said himself”), or that this is a version of “said” that does take NPs. We will come back to the question of the proper analysis of examples like this one below.
This leaves us with the strategy we will implement in the following section: using constructions to realize the pseudo-formal rule S[f rag]→(ADV)X P.7But before we come to this, we have to say a few words about how the semantic formalism we use,MRS, can be incorporated into the semantic component of anHPSG.