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<Paper uid="P84-1026">
  <Title>SYNTACTIC AND SEMANTIC PARSABILITY</Title>
  <Section position="10" start_page="118" end_page="120" type="concl">
    <SectionTitle>
10. CONCLUSION
</SectionTitle>
    <Paragraph position="0"> The arguments originally given at the start of the era of generative grammar were correct in their conclusion that NL's cannot be treated as simply regular sets of strings, as some early information-theoretic models of language users would have had it. However, questions of whether NL's were CFL's were dismissed rather too hastily; English was never shown to be outside the class of CFL's or even the DCFL's (the latter question never even having been raised), and for other languages the first apparently valid arguments for non-CFL status are only now being framed. If we are going to employ supra-CFL mechanisms in the characterizing and processing of NL's, there are a host of items in the catalog for us to choose among. I have shown that semantic filtering is capable of enhancing the power of a CF-PSG, and so, in many different ways, is relaxing the finiteness condition on the nonterminal vocabulary. Both of these  moves are likely to inflate expressive power quite dramatically, it seams to me. One of the most modest extensions of CF-PSG being explored is Pollard's head grannnar, which has enough expressive powe# to handle the cases that seem likely to arise, but I have suggested that even so, it does not seem to be the right formalism to cover the case of the complex nouns in the lexicon of Sambare. Something different is needed, and it is not quite clear what.</Paragraph>
    <Paragraph position="1"> This is a familiar situation in linguistics.</Paragraph>
    <Paragraph position="2"> Description of facts gets easier as the expressive power of one's mechanisms is enhanced, hut choosing among alternatives, of course, get harder. What I would offer as a closing suggestion is that until we are able to encode different theoretical proposals (head grammar, string transformations, LFG, unification grammar, definite clause grammar, indexed grammars, semantic filtering) in a single, implemented, well-understood formalism, our efforts to be sure we have shown one proposal to be better than another will be, in Gerald Gazdar's scathing phrase, &amp;quot;about as sensible as claims to the effect that Turing machines which employ narrow grey tape are less powerful than ones employing wide orange tape&amp;quot; (1982, 131). In this connection, the aims of the PATE project at SRI International seem particularly helpful. If the designers of PATE can demonstrate.that it has enough flexibility to encode rival descriptions of NL's like English, Bambara, Engenni, Dutch, Swedish, and Swiss German, and to do this in a neutral way, there may be some hope in the future (as there has not been in the past, as far as I can see) of evaluating alternative linguistic theories and descriptions as rigorously as computer scientists evaluate alternative sorting algorithms or LISP implementations.</Paragraph>
  </Section>
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