The construction of ‘conjunction+ 하다’ works as single unit in a sentence and its has a new meaning which cannot be explained with compositionality. In this thesis, I call this kind of single unit as ‘construction’ and give a position as a grammatical unit. I investigated the non-separability to prove that ‘conjunction+하다’ construction is single unit. It cannot allow putting any other grammatical constituent in between and its whole construction can have anaphoric phenomenon. Also conjunction cannot be separated from ‘하다’ in cleft sentence. I also investigated the presence of ‘construction’ in the sentence through the syntagmatic relation with the representative grammatical category of Korean language like ‘tense’, ‘honorifics’ and ‘modality’. Modality of ‘conjunction+하다’ construction can be recognized as ‘Intention’, ‘Desire’, ‘Obligation’, ‘Causative’.
