||This thesis presents a semantic and pragmatic inquiry into 'A', 'BA', 'MA', and 'NE', the four modal particles ubiquitous in colloquial Pekinese, in a broad functional approach. It diverges from the wealth of previous studies on the same subject in a number of ways. First, this research makes use exclusively of oral data of casual conversations collected primarily via fieldwork, thereby assuring a high degree of homogeneity and authenticity of data. Secondly, it examines the meaning and use of particles vis-à-vis sentence types and types of conversational situations they occur in, with particular emphasis on the interplay between particles and situations. Thirdly, it is the first thesis-length attempt to explore the semantics of Chinese particles in the framework of Natural Semantic Metalanguage (NSM) proposed by Wierzbicka (1996), aiming to demonstrate how the approach may shed new lights on previously inexplicable problems or unexplored areas in Chinese linguistics. Through a close examination of how the particles convey speakers' attitude or emotional state in different conversational situations, this study shows that the cluster of different, often seemingly unrelated meanings and uses of a particle are coherently interconnected with one another, forming a network that could be adequately characterized as a "Radial Category".