This book deals with the traditional problem of the classification of linguistic units, with a primary focus on word classes. The approach is descriptive rather than theoretical, and is based on the use of distinctive features analogous to the ones used in phonology, which entails a radical reworking of the traditional classification. The first part presents some basic notions such as the use of distinctive features and the role of word classes in grammar; classification by prototypes; and the use of world knowledge as a resource to assign...