In the modern Korean language, the postposition `Da-ga` takes different forms from other postpositional particles. This is because the postposition `Da-ga` grammaticalized from the transitive verb `Da-geu-da` in the middle Korean language shows its morphological characteristics in the modern Korean language intactly. The postposition `Da-ga` needs to be preceded by `E`, `Lo`, `E-ge`, `Han-te` The only combinable substantives are `Eo-di`, `Yeo-gi`, `Jeo-gi`, `Geo-gi` and they derive from the semantic distinctiveness of spatial pronoun. Thus, the postposition `Da-ga` semantically functions as auxiliary particles or postpositional particles. However, it is still in the course of grammaticalization in that it morphologically has more restrictions than general auxiliary particles or postpositional particles. Also, the postposition `Da-ga` is relatively unconstrained from the conservativeness of literary language because it is largely used in colloquial language. Thus, it is difficult to anticipate when or in what form its rate of grammaticalization will rapidly increase, but it can be seen that the postposition `Da-ga` will function as a grammatical form that is classified into auxiliary particles morphologically as well as semantically if it becomes possible to combine alone with a preceding noun phrase or it becomes less restricted to combine with postpositional particles.