This book is written by Professor Yuan Yulin and his co-workers on the basis of Prof. Yuan’s more than 10 years’ research on the membership-based classification of parts of speech in Chinese. 
The classification of parts of speech is the basis for grammatical studies, usually taking the grammatical functions of words as the basis, which however may result in numerous sub-categories as few words have exactly the same function. Therefore, parts of speech are classified into broad categories, each category with some words having a higher degree of membership than others. Applying the prototype theory in cognitive psychology to the studies of Chinese language, the authors of the book have created some scales to measure whether a word belongs to a certain category and to what degree it belongs to the category, bringing about a relatively feasible method and a fuzzy classification of parts of speech. 
The book has two parts: the first part gives a detailed explanation on the altogether four scales for notional words, function words, pronouns, and numeral-classifier compounds and special small categories; the second part applies these scales to a fuzzy classification of more than 900 entries. The methods and ideas in this book can provide inspiration for researches on the classification of parts of speech in Chinese among other aspects of the studies on Chinese grammar.