University of Pennsylvania ScholarlyCommons IRCS Technical Reports Series Institute for Research in Cognitive Science May 1996 What Does a Grammar Formalism Say About a Language? James Rogers University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/ircs_reports Rogers, James, "What Does a Grammar Formalism Say About a Language?" (1996). IRCS Technical Reports Series. 13. https://repository.upenn.edu/ircs_reports/13 University of Pennsylvania Institute for Research in Cognitive Science Technical Report No. IRCS 96-10. This paper is posted at ScholarlyCommons. https://repository.upenn.edu/ircs_reports/13 For more information, please contact [email protected]. What Does a Grammar Formalism Say About a Language? Abstract Over the last ten or fifteen years there has been a shift in generative linguistics away from formalisms based on a procedural interpretation of grammars towards constraint-based formalisms—formalisms that define languages yb specifying a set of constraints that characterize the set of well-formed structures analyzing the strings in the language. A natural extension of this trend is to define this set of structures model-theoretically—to define it as the set of mathematical structures that satisfy some set of logical axioms. This approach raises a number of questions about the nature of linguistic theories and the role of grammar formalisms in expressing them. We argue here that the crux of what theories of syntax have to say about language lies in the abstract properties of the sets of structures they license. This is the level that is most directly connected to the empirical basis of these theories and it is the level at which it is possible to make meaningful comparisons between the approaches. From this point of view, grammar formalisms, or (formal frameworks) are primarily means of presenting these properties. Many of the apparent distinctions between formalisms, then, may well be artifacts of their presentation rather than substantive distinctions between the properties of the structures they license. The model-theoretic approach offers a way in which to abstract away from the idiosyncrasies of these presentations. Having said that, we must distinguish between the class of sets of structures licensed by a linguistic theory and the set of structures licensed by a specific instance of the theory—by a grammar expressing that theory. Theories of syntax are not simply accounts of the structure of individual languages in isolation, but rather include assertions about the organization of the structure of human languages in general. These universal aspects of the theories present two challenges for the model-theoretic approach. First, they frequently are not properties of individual structures, but are rather properties of sets of structures. Thus, in capturing these model-theoretically one is not defining sets of structures but is rather defining classes of sets of structures; these are not first order properties. Secondly, the universal aspects of linguistic theories are frequently not explicit, but are consequences of the nature of the formalism that embodies the theory. In capturing these one must develop an explicit axiomatic treatment of the formalism. This is both a challenge and a powerful beneft of the approach. Such re-interpretations tend to raise a variety of issues that are often overlooked in the original formalization. In this report we examine these issues within the context of a model-theoretic reinterpretation of Generalized Phrase-Structure Grammar. While there is little current active research on GPSG, it provides an ideal laboratory for exploring these issues. First, the formalism of GPSG is expressly intended to embody a great deal of the accompanying linguistic theory. Thus it provides a variety of opportunities for examining principles expressed as restrictions on the formalism from a model-theoretic point of view. At the same time, the fact that these restrictions embody universal grammar principles provides us with a variety of opportunities to explore the way in which the linguistic theory expressed by a grammar can transcend the mathematical theory of the structures it licenses. Finally, GPSG, although defined declaratively, is a formalism with restricted generative capacity, a characteristic more typical of the earlier procedural formalisms. As such, one component of the theory it embodies is a claim about the language- theoretic complexity of natural languages. Such claims are difficulto t establish for any of the constraint- based approaches to grammar. We can show, however, that the class of sets of trees that are definable within the logical language we employ in reformalizing GPSG is nearly exactly the class of sets of trees definable within the basic GPSG formalism. Thus we are able to capture the language-theoretic consequences of GPSGs restricted formalism by employing a restricted logical language. Comments University of Pennsylvania Institute for Research in Cognitive Science Technical Report No. IRCS 96-10. This technical report is available at ScholarlyCommons: https://repository.upenn.edu/ircs_reports/13 Institute for Research in Cognitive Science What Does a Grammar Formalism Say About a Language? James Rogers University of Pennsylvania 3401 Walnut Street, Suite 400C Philadelphia, PA 19104-6228 May 1996 Site of the NSF Science and Technology Center for Research in Cognitive Science IRCS Report 96--10 What Do es a Grammar Formalism SayAbouta Language James Rogers Institute for Research in CognitiveScience UniversityofPennsylvania Suite C Walnut Street Philadelphia PA jrogerslinccisupennedu May Abstract Over the last ten or fteen years there has b een a shift in generative linguisti cs away from formalisms based on a pro cedural interpretation of grammars towards constraint based formalismsformali sms that dene languages by sp ecifying a set of constraints that characterize the set of wellformed structures analyzing the strings in the language A natural extension of this trend is to dene this set of structures mo deltheoreticall y to dene it as the set of mathematical structures that satisfy some set of logical axioms This approach raises a numb er of questions ab out the nature of linguisti c theories and the role of grammar formalisms in expressing them We argue here that the crux of what theories of syntax havetosay ab out language lies in the abstract prop erties of the sets of structures they license This is the level that is most directly connected to the empirical basis of these theories and it is the level at which it is p ossible to make meaningful comparisons b etween the approaches From this p oint of view grammar formalisms or formal frameworks are primarily means of presenting these prop erties Many of the apparent distinctions b etween formalisms then maywell b e artifacts of their presentation rather than substantive distinctions between the prop erties of the structures they license The mo deltheoretic approach oers a wayinwhich to abstract away from the idiosyncrasi es of these presentations ween the class of sets of structures licensed Having said that wemust distinguis h b et by a linguisti c theory and the set of structures licensed by a sp ecic instance of the theoryby a grammar expressing that theory Theories of syntax are not simply ac counts of the structure of individu al languages in isolation but rather include assertions ab out the organization of the structure of human languages in general These universal asp ects of the theories presenttwochallenges for the mo deltheoretic approach First they frequently are not prop erties of individu al structures but are rather prop erties of sets of structures Thus in capturing these mo deltheoreticall y one is not dening sets of structures but is rather dening classes of sets of structures these are not rstorder prop erties Secondly the universal asp ects of linguisti c theories are frequently not ex plicit but are consequences of the nature of the formalism that emb o dies the theory In capturing these one must develop an explicit axiomatic treatment of the formalism This is b oth a challenge and a p owerful b enet of the approach Suchreinterpretations tend to raise a variety of issues that are often overlo oked in the original formalization In this rep ort we examine these issues within the context of a mo deltheoretic rein terpretation of Generalized PhraseStructure Grammar While there is little current active research on GPSG it provides an ideal lab oratory for exploring these issues First the formalism of GPSG is expressly intended to emb o dy a great deal of the ac companying linguistic theoryThus it provides a variety of opp ortunitie s for examining principles expressed as restrictions on the formalism from a mo deltheoretic p ointof view At the same time the fact that these restrictions emb o dy universal grammar principles providesuswithavariety of opp ortunities to explore the wayinwhich the linguistic theory expressed by a grammar can transcend the mathematical theory of the structures it licenses Finally GPSG although dened declaratively is a formalism with restricted generative capacitya characteristic more typical of the earlier pro ce dural formalisms As such one comp onent of the theory it emb o dies is a claim ab out the languagetheoretic complexity of natural languages Such claims are dicult to es tablish for any of the constraintbased approaches to grammar We can show however that the class of sets of trees