Discovery Of Sense Classification Features Of Semantic Gradience Of Modal Verb Ought To

Sense indeterminacy exists in natural languages,which always causes great difficulty for the sense understanding.Sense indeterminacy includes semantic ambiguity,semantic merger and semantic gradience.As a major word-class for emotion and attitude expression,modal verb and its indeterminacy have attracted much attention from experts in the fields of semantics,pragmatics,functional linguistics and cognitive linguistics.With the continuous improvement of science and technology,the application of advanced computer technology into the natural language processing has become a new research direction to solve the sense indeterminacy of natural language.Based on a 6 million words corpus and the sense categorization of modal verb ought to of Coates(1983),the discovery of sense classification features of semantic gradience of ought to is carried out by Filter-APOSD method in this thesis.The semantic gradience of modal verb ought to is categorized into two basic senses: strong obligation and weak obligation.Then the sense of each ought to in the corpus is tagged,and 100 sample sentences of each sense are selected as the research objects.The semantic features,syntactic features,pragmatic features and genre features are also extracted from the context in which ought to occurs.After that,a formal context taking the 200 sample sentences as objects and the extracted contextual features as attributes is constructed.The Filter-APOSD method is then applied for the word sense disambiguation of ought to,the WSD accuracy reaches 96.5%.The sense classification features of semantic gradience of modal verb ought to are discovered from the WSD rules: syntactic features have strong semantic gradience classification function,among these syntactic features “passive voice”,“negation” and“the co-occurrence with words: really,certainly,of course” could classify the sample sentences expressing root strong obligation from the semantic gradience of ought to;and“progressive aspect”,“perfect aspect”,“the co-occurrence with hedge words: perhaps,probably,may” could classify the sample sentences expressing root weak obligation from the semantic gradience of ought to.Semantic features have different classifying functions for the semantic gradience of ought to.And among the pragmatic features,the one that have strong function for semantic gradience classification is “the speaker’s authority over the subject”.Genre features have no direct semantic gradience classifying function for modal verb ought to.It is hoped that the research results of this thesis could provide effectively theoretical support and practical foundation for the study of semantic gradience of English modal verbs and natural language processing.