A Semantic Study Of Must

English modality has become one of the most important categories after obtainedrecognition in the domain of linguistics. Many scholars have paid great attentions toEnglish modality, and argue about its fuzziness. The modality is expressed in variouskinds of grammatical ways, Modals are considered the most obvious and typical form torealize modality, and the core modals are commonly known as can, may, must, will andshall. So must as the most powerful modal verb among the core modals attracts manyscholars, and the author’s attention.Scholars try to study the limitation of the usage of must and polysemy of themeaning of it from the perspective of traditional grammar, semantics and pragmatics. Inthe field of cognitive linguistics, scholars have proposed new ways for the study relatedto must. For instance, Johnson (1987) proposed Force Schemas; Talmy (1988) imposedthe notion of Force Dynamics and Sweetser (1990) put forward Metaphorical Projection.Researchers put great emphasis on the influence of speakers’ cognitive knowledge onthe semantic meanings of must. Based on the previous studies, the researcher attemptsto study must in terms of force dynamics, and to reveal the cognitive rules about it.Winter and Gardenfors (1994) propose that the social power relations aresemantically fundamental and psychological conflict and physical compulsion arederived from it. This is because in the society language is a main tool of communication,and the interpersonal communication is determined by the social regulations.Based on the previous notions, the researcher analyzes the examples (thoseexamples are found in Collins COBUILD English Dictionary, COCA and BNC corpus)and finds out that of the sentence with deontic must, the compulsory force opposes thefocal entity is the social force, and the outcome of the force conflict between them is thesocial action. As to the sentence with epistemic must, the compulsory force opposes thefocal entity is the psychological force, hence the outcome of the force conflict betweenthem is the psychological action. And as to the sentence with dynamic must, thecompulsory force opposes the focal entity is the natural force, thus the outcome of theforce conflict is the physical action or abstract action. These notions are closely related with people’s knowledge level and cognitive experiences. Based on the previousanalysis, the author also finds out that force dynamics can be used to clear theambiguity of the deontic necessity, obligation and invitation of must; epistemicprobability, confident inference and inevitability of must; and dynamic sense necessityof must.On the basis of previous studies of must, this thesis has made a force dynamicanalysis of must, which can be regarded as a complement to the study of modal verbs.