Situational Investigation of Presuppusition

SITUAT]Or~JA L Selkl Akama Fujitsu I.td. 2-~-19, ShinYokohama, Yokohama, Japan INVESTIGA-I-ION [Jl- PRESUPI-~[.Jbl I IUIX,I Masahlto RawamorI Sophia University, 2 Kieicho, Chivodaku Tokyo, Japan Abstract This paper gives a formal theory of presupposition using situation semantics developed by Barwise and Perry, We will slightly modify Barwise and Perry's original theory of situation semantics so that we can deal with non-monotonic reasonings which are very important for the formalization of presupposi- tion in natural language. This aspect is closely related to the formalization of incomplete knowledge in artificial intelligence, 1. Introduction In constructing a natural language understanding system we face,serious problems in syntax, semantics and pragmatlcs, From a computational point of view, pragmatics especially poses the greatest problem. At present there exists no appropriate theory of pragmatics for natural language. A few approaches proposed so far seem to offer linguistic or compu- tational difficulties in their foundation, for they never give a computational mechanism for pragmatics in an effective way. In understaqding the meaning of a natural language we use both the knowledge for the language and the so-called world know~ Most of the inferences used in natural language can be dependent upon the latter. Many researchers, however, have ignored in their formalism this aspect of natural language reasonings. We believe that a desirable formalism must include two important devices: firstly a representation of world knowledge: secondly, an inference system involved in the world knowledge. The forme," has already been realized in many A] systems, while the latter cannot be found in most systems. As for the latter," although there are such non-classical systems as non-monotonic logics and fuzzy logic, a more suitable inference system for incomplete knowledge is definitely in need. And linguistic observations have shown that traditional model-theoretic formalisms are inadequate in this respect. Presupposition is essential In understanding natural language. The possibility of suspending presuppositions of a sentence shows that presupposition has lobe undarstobd as an inference in an incompletely perceived world. Hence con- structing a theory of natural language reasonings as presup. position calls for one" Incorporating non-monotonic reasonings, From such considerations we choose Situation Semantics (henceforth SS) developed by Barwise and Perry (1983) as a basis of our theory. In SS the meaning of a sentence is repre- sented as a relation between the situations in which the sentence is uttered and the situations described by such utterances. We take presuppositions to be information about the described situations consistently restricted by the uttered situations. In section Z we review presupposition briefly. The subsequent sections will provide a theoretical foundation for it on the basis of 5S. 2, Presupposition Before formalizing pr(~supposition, we shah consider the important question: "what is a presupposition?" The answer to this question Is the kev to the construction of a formal theory of presupposition. We find in the literature- several definitions of presup- position. For example, many philosophers and linguists assume the definition generally represented as follows: (Def 1) A presupposes 8 iff (i) A entails B 00 -A entails B This …

Content truncated to 500 words