The objective of language is well-known to everybody as mutual communication. But we would like to add the correctness as features of complete communication. Therefore, we can say that language exists for correct communication. For developing the correctness of communication, we try to know and be skilled in using grammatical means as pronunciation rules, orthography, syntactic rules, discourse rules and stylish effect. For the consideration of teaching correct Korean language, we have to know the difference between colloquial(spoken style) and literary (written style) Korean. As language changes consistently, these two styles always are in contradictory relation. According to the change of colloquial language, reformation of literary form of language will be followed. There are two rules in grammar rules. One is prescriptive rule by which we should say and write, and another is descriptive rule by which we say and write according to degree of generalization in language use. In teaching school grammar teachers have to use these two rules. In a transitional period with conflict, teaching Korean language introduces some colloquial dialogues that can show the incorrect forms in orthography sometime, for examples as -구, -길래(correct form: -고, -기에). In this case we see the conflict between colloquial use and literary misuse. We have to make a standard criterion of how to select colloquial form or literary form. We conclude to introduce literary forms in the colloquial dialogues to prevent learner`s confusion when learners read the written texts consisted of orthographic forms after learning the colloquial forms someday. We also propose the learning by principle and cognition for learning Korean grammar and orthography.