Abstract 0. Introduction 1. The Notion of Grammatical Categories 2. Verb Ha as the Representative Grammatical Verb in Korean 2.1. Verb Ha in Head Position of a VP 2.2. Verb Ha Inserted by Transformation 2.3. Grammatical Verb Ha under the INFL Node 3. 'Grammaticalized' Open Verbs in Serial Verb Constructions 4. Conclusion References