This paper elucidated the concept and units of discourse(text) through comparing with phonemes, morphemes, words and sentences. Especially words or sentences that are abstract reality are used interchangeably with Korean language units(discourses, utterances) as concrete reality for convenience. But This paper demonstrated that the type of abstract reality such as phonemes, morphemes, words and sentences should be differentiated from the type of concrete reality such as discourses and utterances in academic argument. As a result, it were clarified that the former can be said as language unit for studying language and the latter can be said as language unit for communication. Furthermore, this article also discussed that paragraph and ``dallak``. (the unit composed over two paragraphs) as language unit for communication can be established. But they are distinguished from discourses and utterances in terms of optional units.