Rapid technological advancements have changed how we all communicate, including how and where we express our opinions. In a democratic society, various opinions must be respected, and this requires rational communication. This study researched the concept of justification as applied to teaching rational communication in Korean language education; justification is the action of demonstrating that something is right or reasonable. We began with the assumption that it is necessary to treat justification as an important agenda in any communication education based on rationality. We critically examined the perspectives of argumentation and rationality education as they are handled currently in Korean language education. Next, we dealt with justification as the principle of procedural rationality acquisition. Procedural rationality means that subjectivity and mutual subjectivity acquire rationality through justification. We then dealt with justification as a social praxis principle; social praxis is the acquisition of rationality through behavioral exchange among members of the community. Finally, we dealt with the application of Korean language pedagogy to justification studies. The results suggest that the justification as the principle of procedural rationality acquisition and social praxis is a useful concept for teaching rational communication. We believe that this justification study can be used to inform contents and evaluation factors in the practice of discourse.